By Brandon Miller and Judson Jones, CNN

Updated 2:41 PM ET, Thu October 14, 2021


Winter weather, ongoing drought conditions and even the remainder of hurricane season will see impacts from a recent cooling of sea surface temperatures in the Pacific. La Niña conditions — the opposite phase of El Niño — have emerged in the tropical Pacific Ocean over the past month, the National Oceanic and Atmospheric Administration’s Climate Prediction Center said ThursdayLa Niña typically brings conditions that are wetter and cooler than average to the Pacific Northwest and northern Plains, especially during the winter.

In contrast, La Niña means drier and warmer-than-average conditions usually prevail in the South. This could mean the drought-stricken Southwest will likely stay drier. (La Niña also was present last winter and worsened the drought situation across the West and Southwest.)

The Southeast is also typically drier during a La Niña winter, though before the season starts, it increases the possibility for tropical weather, including hurricanes. 

La Niña will persist through winter in the US

La Niña — translated from Spanish as “little girl”– is a natural ocean-atmospheric phenomenon marked by cooler-than-average sea surface temperatures across the central and eastern Pacific Ocean near the equator that consequently impact weather across the world.

“La Niña is anticipated to affect temperature and precipitation across the United States during the upcoming months,” the center said as it issued a La Niña advisory Thursday, predicting conditions are present and expected to remain. California’s Alisal Fire threatens power outages, prompts evacuations and sparks concerns over Ronald Reagan’s Rancho del CieloThe advisory replaces the La Niña Watch, which indicated favorable conditions for development that had been in place since July.NOAA will release its winter outlook October 21, and the presence of La Niña is expected to weigh heavily in the forecast for the season. The prediction center put the odds near 90% that La Niña would be in place through the winter of 2021-2022.Both La Niña and El Niño occur every three to five years on average, according to NOAA.

La Niña and the climate crisis

While El Niño and La Niña events are regular aspects of global weather patterns, increased global temperatures may temper or change their effects.La Niña tends to pull down global temperatures, but in recent years, the planet has warmed so fast, it’s like hitting a small speed bump at 80 mph — it barely even registers.18 weather and climate disasters this year have killed over 500 people and cost over $100 billion in US

It’s likely too early to know how climate change will affect those patterns; research is beginning to show how a warming climate may amplify the effects of El Niño and La Niña. Climate change could increase the severity of weather events stemming from El Niño and La Niña patterns, according to a 2018 study on atmospheric conditions that ran simulations of climate conditions.Top spots on the warmest-years list used to be reserved for the strong El Niño years, but human influences have long since overwhelmed the planet’s natural temperature regulators. For instance, La Niña was present during parts of 2020, but the year still tied with 2016 (an El Niño year) as the hottest on record for the plane



La Niña is back. Here’s what that means ~ THE WASHINGTON POST

The atmospheric and oceanic pattern will have a bearing on the Western drought, the end of hurricane season and the forecast for winter and spring

Global sea surface temperature anomalies in degrees Celsius. (Climate Reanalyzer)

By Matthew CappucciYesterday at 2:22 p.m. EDT

After a months-long period of relative atmospheric balance between El Niño and La Niña, the National Oceanic and Atmospheric Administration announced Thursday that La Niña has returned. It’s expected to stick around in some capacity through the winter and relax toward spring.

The intensifying La Niña should peak in magnitude, or strength, by the end of 2021, having bearings on the drought in the West, the end of hurricane season and the upcoming winter. La Niña also plays a role in shaping how tornado season pans out in the spring.

Frigid West, warm East: Continent divided between clash of seasons

It’s one of many drivers in our atmosphere, but it is often among the most important given the extent to which it shuffles other atmospheric features key in determining how weather evolves over the Lower 48.

In brief, here are some of the key impacts La Niña could have in the coming months:


  • Extending favorable conditions for Atlantic hurricane activity this fall.
  • Worsening drought conditions in the Southwest through the winter and potentially elevating the fire risk through the fall.
  • Raising the odds of a cold, stormy winter across the northern tier of the United States and a mild, dry winter across the South.
  • Increasing tornado activity in the Plains and South during the spring.

La Niña is the opposite of El Niño, which often makes headlines for spurring powerful southern storms that can generate beneficial rains in California and track across the entire nation. During La Niña, such winter storms tend to be less frequent.

About six weeks remain until the start of meteorological winter (Dec. 1), and forecasters are already looking ahead to what may be in store. There’s still a long way to go before the first flakes fly in most places, but some meteorologists are already tossing their hats in the ring, trying to broadly gauge what lurks ahead.

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What is La Niña?

A schematic for a traditional La Niña. (

La Niña begins with a cooling of waters in the eastern tropical Pacific. The basin alternates between El Niño and La Niña every two to seven years on average. That pocket of cooler ocean water chills the air above it, inducing a broad sinking motion. It’s that subsidence, or downwelling of cool air, that topples the first atmospheric domino.

During La Niña winters, high pressure near the Aleutian chain shoves the polar jet stream north over Alaska, maintaining an active storm track there. The Last Frontier often ends up cooler than average. The confluence of the polar and Pacific jet streams, as shown in the image above, helps drag some of that cold air across the Pacific Northwest and adjacent parts of the northern Plains.

That keeps the northern United States anomalously wet, while the South is left largely warm and dry. This is bad news for California and other parts of the Southwest, which are enduring a historic drought. The persistence of warm, dry conditions would cause the drought to worsen and potentially prolong the fire season.

La Niña arrived in fall 2020 before fading away in May 2021. Neutral conditions, bridging the divide between La Niña and El Niño, prevailed through the early fall before the NOAA’s declaration of La Niña’s return Thursday.

La Niña tends to exert a slight cooling effect on global temperatures, but recent La Niña years are warmer than El Niño years were just a decade ago because of the warming influences of human-caused climate change. Even with La Niña influencing global temperatures, 2021 still has a greater than 99 percent chance to rank among the top 10 warmest years on record, according to the NOAA.

~~~ CONTINUE ~~~


Predictive models forecast what will happen in the future. These models work because natural events often follow pattern

To calculate the probability of a future outcome, most predictive models factor in historical data along with what we know about rules and relationships among the variables involved.

Because they deal with the future, which hasn’t happened yet, all predictive models have a degree of uncertainty. So most predictive models include some way to communicate the nature of that uncertainty.Sources of Uncertainty in Predictive Models

  • Human error in data collection
  • Accuracy of measuring equipment
  • Precision of data collection device
  • Historical conditions no longer apply
  • Random behavior of the system itself, no pattern
  • Important variables left out of the model
  • The predictive model itself influences the outcome
Uncertainty in Prediction Models

Weather Forecasts: A Familiar Predictive Model

NASA Satellite

When you check the weather forecast, you are relying on a predictive model—a model that has come a long way since the days when we relied on grandma’s trick knee.

Modern weather forecasting uses a staggering amount of technology. Weather stations and satellites work around the clock to collect climate data. Powerful supercomputers plug this data into mathematical equations that make up complex computer simulations.

Because earth’s atmosphere is chaotic and highly variable, supercomputers can’t just run one simulation and call it a day. They have to run many, many thousands of simulations, plugging in different values within a range for things like temperature and air pressure.

This method, called Monte Carlo Analysis, helps account for uncertainty. Thanks to robust computer modeling, the prediction accuracy of weather events, like the path a hurricane will take, has increased threefold since the 1980s.

The Wisdom of Crowds

Many modern prediction methods use ensemble forecasting, a type of Monte Carlo analysis that combines the results of multiple independent forecasts. These forecasts come from groups of scientists around the world who have all developed their own models, each using a slightly different approach to predict outcomes.

By combining the collective opinions of a group of experts, we get a better forecast. This broader view helps account for variability, and it makes trends more visible. But in order for it to work, each individual must be independent, and the group must represent diverse perspectives and ideologies.

NASA Forecast
Ensemble Example

Predictive Models and Risk

Because they lay out the possible consequences of the choices we make, models can inform decisions and policies.

Risk is the chance you might lose something of value. Predictive models that forecast risk often go hand in hand with policy decisions.

Auto insurance companies use predictive models to decide how much to charge you for a policy. If the models predict you are high risk, you have to pay more.

Health care systems use predictive models to forecast patient disease risk. By knowing ahead of time the likely populations that will be affected by particular diseases, they can better target interventions for those who need them most.

Sea Rise

A wet pattern for the Southwest ~ OpenSnow

A surge of monsoonal moisture in conjunction with the remnants of Pacific Hurricane Nora will result in widespread showers and t-storms along with the potential for flash flooding across the Four Corners states.

Short Term Forecast

Numerous large fires are burning across California, resulting in widespread smoke and air quality issues along with threats to local communities.

The Caldor Fire has forced an evacuation of the entire town of South Lake Tahoe (22,000 people). As of Tuesday, the fire had burned across portions of Sierra-at-Tahoe Ski Resort and is threatening other ski resorts in the area such as Kirkwood and Heavenly, not to mention large numbers of homes and structures.

Unfortunately, windy conditions are expected to continue on Wednesday and to a lesser extent Thursday, which along with low relative humidity will result in high spread potential.

Here is the wind gust forecast map for Wednesday morning:

Winds are expected to decrease to a greater extent on Friday (good news), but daytime relative humidity values will continue to be quite low with poor overnight recovery (bad news).

Smoke from the numerous fires across California will continue to impact air quality across California, Nevada, and downwind states. 

On Wednesday, the smoke plume will extend northeast into portions of Utah, Eastern Idaho, and Wyoming due to southwesterly winds (from the southwest) aloft. Smoke will also impact areas east of the Continental Divide in Wyoming and Colorado, including Denver Metro. 

Thursday’s pattern will be similar with just a slight southward shift in the smoke.

Forecast Smoke (surface)

Forecast Smoke (sky)

Current Air Quality

Heading into Labor Day weekend, winds aloft will start to shift to west/northwest resulting in a southward shift in smoke, with higher impacts over Utah, Colorado, and Northern Arizona and New Mexico.

Smoke and fire issues aside, a fairly active weather pattern is in place over the Intermountain West during the middle part of this week.

A large trough of low pressure is located over the Western U.S. with multiple embedded disturbances. 

Southwest flow and abundant energy from this pattern is interacting with monsoonal moisture along with the remnants from Pacific Hurricane Nora to result in wet conditions and even a flash flooding risk across parts of Arizona, Utah, Colorado, and New Mexico.

Ongoing showers and thunderstorms across Utah and Arizona on Wednesday morning will spread into Western/Central Colorado and Northern/Central New Mexico on Wednesday afternoon with widespread wetting rains expected.

Current Radar

Lightning Density

Forecast Radar

After an active middle of the week, the pattern will quiet down heading into Labor Day weekend with a weak ridge of high pressure building over the Western U.S.

Despite the mid-week rainfall, temperatures over the next 5 days will generally be above average across the Central Rockies, Great Basin, and California, and near to below average across the Northwest as well as Southern Arizona.

Forecast for Wednesday, September 1st

A wet day is in store throughout the Four Corners region with the heaviest rainfall expected across Southern Utah, Eastern Arizona, Western Colorado, and Northern/Western New Mexico. Only isolated showers/t-storms can be expected farther north into Wyoming and perhaps Montana.

Forecast for Thursday, September 2nd

Scattered showers and thunderstorms can be expected again across the Four Corners region, possibly starting early in the day. Meanwhile, a disturbance moving across the Northern Rockies will produce some shower/thunderstorm activity across Montana, Idaho, and Wyoming on Thursday afternoon and Thursday night.

Forecast for Friday, September 3rd

Shower and thunderstorm activity will linger across the Northern Rockies on Friday morning, and perhaps into Friday afternoon east of the Continental Divide. Monsoonal moisture will remain in place across the Four Corners states with another solid round of afternoon showers and thunderstorms expected.

Forecast for Saturday, September 4th

Conditions will dry out across the Northern Rockies, while the Four Corners region will see another round of afternoon thunderstorms with less coverage compared to prior days. A fairly strong storm system will also impact coastal portions of British Columbia, with some rain extending south onto the Olympic Peninsula and to a lesser extent the Washington Cascades.

Forecast for Sunday, September 5th

A drying trend is expected with a weakening monsoon and afternoon thunderstorms mainly confined to Arizona and New Mexico. A few light showers are also possible across the North Cascades.



The extreme and unforgiving heat wave in the West, which has set hundreds of records since Sunday, made history again on Thursday as temperatures surged to their highest levels yet. It is poised to maintain its grip on the sizzling Southwest through Saturday before slowly subsiding.

The heat wave, like most, is the result of a sprawling zone of high pressure popularly known as a heat dome. Common in summer, heat domes are often found over the Four Corners region of the Southwest United States, where intense heating occurs over deserts.

However, the heat dome wreaking havoc across the western United States this week is striking for its incredible strength, geographic scope and persistence. Evidence suggestshuman-caused climate change is making these heat domes more intense over time.

This lengthy list of temperature records on Thursday, from California to Nebraska and far from comprehensive, is a testament to this heat dome’s might:

  • Palm Springs, Calif., matched its highest temperature ever recorded, soaring to 123 degrees.
  • Death Valley, Calif., hit 128 degrees, the highest temperature measured anywhere on the planet so far this year and just one degree off its June record of 129 set on the 30th in 2013.
  • Phoenix hit 118 degrees, a record for the date, and the earliest the city has observed a temperature this high. “Only 18 other days in Phoenix’s period of record have reached 118° or greater,” tweeted the National Weather Service office in Phoenix.
  • Denver reached at least 100 degrees for the third straight day, the earliest occurrence of such a streak on record. “[A]ll of the 100°F streaks in Denver history lasting three or more days have occurred in the past 32 years,” tweeted Bob Henson, a meteorologist and weather journalist. “Denver’s climate record goes back 150 years.”
  • Tucson reached at least 110 degrees for a sixth straight day, tied for the longest streak on record.
  • Las Vegas’s low temperature of 90 degrees was its warmest on record so early in the season. It also set a daily record high of 114 degrees.
  • Sacramento set a daily record high of 109 degrees, shattering the previous record of 102.
  • Omaha set a daily record high of 105 degrees, its hottest June day since 1953 and its third highest June temperature.

People wait in line for snow cones during a heat wave in Dallas on Thursday. Texas is pushing homes and businesses to conserve electricity for a second day in a row to stave off blackouts. (Kathy Tran/Bloomberg News)

This flurry of heat-dome-driven records follows temperatures that matched all-time highs on Tuesday in parts of Utah, Wyoming and Montana. Salt Lake City, Sheridan and Laramie, Wyo., and Billings, Mont., all made history, soaring to 107, 107, 94 and 108 degrees, respectively.

On Wednesday, Las Vegas soared to 116 degrees, one shy of its highest temperature ever recorded, while Grand Junction, Colo., hit 105, matching its highest temperature ever observed in June.

How a heat dome works

Hot air masses expand vertically into the atmosphere, creating a dome of high pressure that diverts weather systems around them. One way to gauge the magnitude of a heat wave is to measure the height of the typical halfway point of the atmosphere — at the 500 millibar pressure level. For this pressure level to stretch to heights of 600 dekameters, or 19,685 feet, is quite rare, but that marker was forecast for this week, and it was indeed reached in Flagstaff, Ariz., on Tuesday.

Alex Tardy, a meteorologist with the National Weather Service in San Diego, noted in an email that what is unusual about this particular heat dome is its strength and size, and the fact that it is only mid-June. A weather balloon in San Diego measured a record temperature of 89.2 degrees in the lower atmosphere on Thursday, which Tardy called a “very significant” reading for this location and time of year. That is translating into scorching temperatures for inland areas and deserts.

As the ground warms, it loses moisture, which makes it easier to heat even more.

As a high-pressure system becomes firmly established, subsiding air beneath it heats the atmosphere and dissipates cloud cover. The high summer sun angle combined with those cloudless skies then in turn further heats the surface.

Hot air masses expand vertically into the atmosphere, creating a dome of high pressure that diverts weather systems around them. One way to gauge the magnitude of a heat wave is to measure the height of the typical halfway point of the atmosphere — at the 500 millibar pressure level. For this pressure level to stretch to heights of 600 dekameters, or 19,685 feet, is quite rare, but that marker was forecast for this week, and it was indeed reached in Flagstaff, Ariz., on Tuesday.

Alex Tardy, a meteorologist with the National Weather Service in San Diego, noted in an email that what is unusual about this particular heat dome is its strength and size, and the fact that it is only mid-June. A weather balloon in San Diego measured a record temperature of 89.2 degrees in the lower atmosphere on Thursday, which Tardy called a “very significant” reading for this location and time of year. That is translating into scorching temperatures for inland areas and deserts.


As a high-pressure system becomes firmly established, subsiding air beneath it heats the atmosphere and dissipates cloud cover. The high summer sun angle combined with those cloudless skies then in turn further heats the surface.

But the vicious feedback loop doesn’t end there: the combination of heat and drought is working to send this heat wave into truly extreme territory. With very little moisture in soils right now, heat energy that would normally be used on evaporation — a cooling process — is instead directly heating the air and ground surface.

Jane Wilson Baldwin, a postdoctoral researcher at the Lamont-Doherty Earth Observatory at Columbia University, said that given the severe drought in the West right now, many feedbacks between the land and the atmosphere are combining to produce an unusually persistent extreme.

“When the land surface is drier, it can’t cool itself through evaporation which makes the surface even hotter, which strengthens the blocking high further,” she said in an interview.

The situation is greatly amplified by increasing background temperatures due to the burning fossil fuels.

“You would be hard-pressed to come up with a metric of heat waves that isn’t getting worse under global warming,” she said, adding that the increasing intensity and duration of heat waves is particularly clear.

Heat waves are often high mortality disasters, but those deaths are preventable, she said, with advance warning, air conditioning, cooling centers and neighbors checking on neighbors.

However, avoiding heat-related disasters also depends on the resilience of the electrical grid, which can fail if electricity demand due to air conditioning use exceeds supply. As a result, there is the double risk of infrastructure failure and health impacts from temperature extremes, as occurred during the Texas freeze of February.

More record heat into Saturday before heat dome weakens

Excessive heat warnings remain in effect for much of California away from the coast and the mountains, western and southern Arizona, southern Nevada and southern Utah.

Temperatures on Friday and Saturday in places like Phoenix, Las Vegas and Sacramento will be about as hot as they were on Wednesday and Thursday.

The hot, dry air underneath this heat dome has created tinderbox conditions conducive to the spread of wildfires. On Friday, the Weather Service warned of a “critical” fire threat from eastern Utah into southern Colorado. The concern is dry thunderstorms that unleash lightning igniting blazes. “Fuels are extremely susceptible to lightning starts given ongoing drought and record heat,” the Weather Service wrote.

By Sunday, computer models indicate the intensity of the heat dome will begin to wane some and drift southeast into northern Mexico and west Texas early next week. At that point, temperatures will still be above normal, but not record challenging.

Mexican dust found in Colorado blizzard ~ CNN

By Jennifer Gray, CNN

Mon March 15, 2021

(CNN)The snowstorm that broke records and brought parts of the Rockies to a standstill had something else that was quite literally buried in the snow: a layer of brownish snow that fell in New Mexico and Colorado with dust that had traveled all the way from Mexico.It was a tweet from the National Weather Service office in Albuquerque, New Mexico, that pointed out the phenomenon.”The dust that was lofted this afternoon from the playas in Mexico … has now been transported all the way into Colorado!” it read. “We had a low that was tracking across the state and it was bringing a lot of gusty winds from the southwest. You could see on the satellite imagery the dust being lofted,” said Sharon Sullivan, meteorologist at the NWS in Albuquerque. 

~~~ WATCH ~~~

The yellow on the NOAA satellite shows the dust being carried north with the winds. Using a filtered layer created by Colorado State University, the dust is easier to pick out in the imagery.Dust even ended up in the snow as far north as Boulder, Colorado, according to the National Weather Service, which tweeted a picture of the brownish layer that fell outside its office.”We don’t see it too often. Especially ending up as far north as Boulder,” said Sullivan. More often, she added, dust will be carried from White Sands National Park, which is in the southern part of the state, but to get it from Mexico is pretty rare.

How the Mexican dust was able to travel so far

The weather setup for this event was perfect. Northern New Mexico and parts of Colorado have had a red flag warning in place for the past several days, so winds were gusting out of the southwest at 60-70 mph at times. Those strong winds helped lift and carry the dust from Mexico.”Some of these particles are very fine, so it only takes about 15-20 mph to have them lifted off the ground,” said Sullivan. So with winds gusting three times that, the dust was easily picked up and carried nearly 800 miles. Similar to the way Saharan dust travels from Africa, across the Atlantic and ends up suspended over the Florida sky, this dust was picked up and carried north. “The dust particles cling to the snowflake or water particle and falls with the snowflake to the ground,” said Sullivan. The result is a fresh coat of snow with a brown hue. Sullivan said the same setup Tuesday could result in more dusty snow, which she says also reduces the snow’s albedo, or reflection power, causing it to melt more quickly and resulting in a reduced snowpack overall. It has been a busy week for that region of the country. The National Weather Service office in Albuquerque had critical fire weather and winter weather advisories, and a tornado watch, at the same time — something that’s not unheard of for that region, but wild nonetheless.


Eye-in-the-sky technology is bringing avalanche science into the 21st century, enabling forecasters with better tools for predicting threats in Colorado’s backcountry.

Bay Stephens

Mar 1, 2021

A 3-D oblique view of terrain near Aspen, CO from April 7, 2019, showing snow depths mapped by the Airborne Snow Observatory. The Maroon Bells are visible at top right, Highland Bowl and Aspen Highlands Ski Area at center-right, and the enormous avalanche in the 5 Fingers avalanche path clearly visible at center. (Jeff Deems, Airborne Snow Observatories, Inc.)

Avalanche forecasting has come a long way since the 1950s, when forecasters relied solely on weather to predict when and where snow might slide. But it still requires scientists skiing and digging into the snowpack. That’s changing as satellites, aircraft-mounted sensors and ground-based remote monitoring fast-track the evolution of snow science, giving experts comprehensive insight into the uncanny nature of avalanches. 

The Colorado Avalanche Information Center has been testing satellite imagery to detect avalanches. The technology is building a more accurate library of avalanche activity over a winter season, and year over year. And not just for the most trafficked zones, said Mike “Coop” Cooperstein, the center’s lead forecaster for the northern mountains. 

“We have really good information along the highways, in the really popular recreation spots — Berthoud Pass, Loveland Pass, Red Mountain Pass. But it’s pretty close to the road,” Cooperstein said. “So we wanted to look into those deeper areas, a few miles from the trailhead, and see what’s happening, because we are forecasting for those areas.”

With 11 avalanche fatalities in Colorado this winter, and 32 nationwide, avalanche forecasters like those at CAIC need all the resources they can get to create accurate forecasts for backcountry regions. But methods of gathering good information are decades old. Emerging technologies may help, but it could be years before they are operational or affordable enough for avalanche forecast centers to use on a daily basis.

Relying on observations shared by travelers on roads and skintracks yields only a partial picture of avalanche activity, and doesn’t necessarily reflect the hazard spread across entire ranges. As a result, during any given avalanche cycle, forecasters may miss part of the avalanche activity because it wasn’t witnessed, and wouldn’t be able to warn their audience of backcountry goers. The other issue is not being able to verify whether their forecast was correct after the fact, making it difficult to identify patterns of inaccuracy and improve forecasts over time.

An avalanche record biased toward easy-to-access areas also leaves researchers in the lurch as they have only a fuzzy quantitative idea of what “normal” is as far as avalanches go. This could complicate understanding how avalanche activity shifts away from historical trends because of climate changes.

To balance and fill in the record, researchers, avalanche forecast centers and private companies are leaning on new technologies.

Late last year, Norway began using satellite-mounted radar to detect avalanches across the country.

The system was developed by a team from the Norwegian Research Center, known as NORCE, using synthetic aperture radar, or SAR, mounted on the European Space Agency’s two Sentinel-1 satellites. When a slide was detected it was automatically reported to Norwegian avalanche forecasters. Because the SAR device emits microwaves toward the Earth’s surface, rather than sensing natural light, this method allows the satellites to capture images on cloudy days or at night. 

A 3-D oblique view of terrain northwest of Crested Butte, Colorado from April 7, 2019. Numerous avalanche release areas and deposits are evident in this Airborne Snow Observatory snow depth image, as indicated by the arrows. (Jeff Deems, Airborne Snow Observatories, Inc.)

When an avalanche releases, the debris pile left at the slope’s base is both rougher and more dense than the surrounding snow, which scatters the microwaves emitted by the SAR so that fewer of them return to the sensor on the satellite. The NORCE team has built what’s called a data processing chain that recognizes this increased “backscatter” and flags it as potential avalanche debris.

The method is not perfect — with accuracy varying on how much water is in the snowpack — but technology is helping the Norwegian avalanche forecasting agency identify thousands more avalanches than any field-based efforts would, said Markus Eckerstorfer, the NORCE researcher who developed the data processing chain.

“In general, the method is very promising,” Eckerstorfer said. “It’s probably better than anything else. If you have a certain region, you could never cover the entire region as you do with a satellite. But you’re still not able to detect everything.”

In 2018, Eckerstorfer received funding from the ESA to test the method in Colorado, teaming up with CAIC. But the test fell flat. 

Colorado’s mid-latitude played a role in the poor results: Because the Sentinel-1 satellites are polar-orbiting, moving between the North and South poles, the closer a region is to the equator, the less coverage it receives. Norway, being so far north, receives daily passes, while Colorado is passed every six or so days. Additionally, during the winter of 2018 one of the pair of satellites stopped sending images of Colorado because it needed time to recharge for imaging Europe and countries that paid to put the constellation into orbit.

An image every 12 days was far less useful for CAIC, and interest in the project dropped off.

“We wanted to have pretty close — a day or two at the most — of detection so that we can, after our forecast, look and see if what we think happened, happened,” Cooperstein said. “For that, there just isn’t enough coverage. There aren’t enough passes over Colorado to do that kind of work right now.”

An avalanche dumped tons of snow and debris in the Conundrum Creek Valley floor beneath the area known as Five Fingers. The massive avalanche started at Highlands Ridge at the top. (Scott Condon, The Aspen Times)

Research using the method continues elsewhere in the states, though, which may one day come back to benefit Colorado.

An avalanche forecasting center in Idaho and another in Montana are using a rudimentary version of NORCE’s automated avalanche detection from Sentinel-1s, led by Zach Keskinen, a snow science master’s candidate at Montana State University. 

Keskinen said the technology would not replace forecasters on skis, but it can be yet another tool in the high-consequence science of predicting avalanches. 

“It’s starting to show promise to where [an avalanche forecaster] could say, ‘Hey, this is where you should go for your field day.’” he said. “Hopefully it will help to guide field days for forecasters and just make their field time more powerful. 

Keskinen expects satellite coverage in the states to improve. The U.S.-Indian NISAR satellite scheduled for launch in 2022, will have SAR sensors.

Despite the low utility of radar in Colorado to date, satellites are still in the mix at CAIC. The organization is using optical imagery instead of radar to review the once-in-a-century avalanche cycle from March 2019, when historic slides swept over Interstate 70, blew out massive swaths of forest and spiked four of Colorado’s avalanche advisory zones into “extreme” avalanche danger.

“We can pick out avalanches from that cycle pretty well with, you know, 90% confidence that we’re picking out avalanches,” Cooperstein said.

CAIC staff can look at destruction of vegetation, or signatures of decaying vegetation, to see where an avalanche has cleared forest, documenting slides that may otherwise have been missed. 

“The thing there is it takes such a large avalanche to destroy trees,” Cooperstein said. “That avalanche cycle, I’ll probably never see another one of those in my career, that’s that big. But [optical satellite imagery] has really good promise and we have pretty good results from doing that.”

A 3-D oblique view of terrain near Schofield Pass from April 7, 2019. Numerous large avalanches are evident in this Airborne Snow Observatory snow depth image. (Jeff Deems, Airborne Snow Observatories, Inc.)

Lasers can detect avalanches, too, specifically light detection and ranging, or LiDAR.

Jeffrey Deems, a researcher at University of Colorado and co-founder of Airborne Snow Observatory (an offshoot of NASA’s Jet Propulsion Laboratory), uses LiDAR mounted on aircraft to measure snow in basins across the western U.S. While the goal of these flights is to map how much snow—and therefore water—a river basin holds so that water managers can better plan how to allocate runoff, they also detect avalanches.

The method works by “mowing the lawn,” as Deems puts it, flying a plane with a LiDAR instrument scanning every foot of an entire river basin. Such a flight path is done in the summer without snow to create a baseline, then again in the winter, allowing Airborne Snow Observatories to subtract the summer image from the winter one to determine snow depth. 

In 2019, flights in the Upper Gunnison and Roaring Fork river basins revealed large avalanches that had not been documented. LiDAR offers a more detailed look into an avalanche than other optical or radar imagery.

“With the LiDAR technology, we can actually see the change in snow depth, so we can actually get a better metric, or a better understanding of the volume of snow that had to move, rather than just mapping the extent of it,” Deems said.

Deems, with colleagues from the U.S. Army Cold Regions Research and Engineering Lab, operate ground-based LiDAR on Loveland Pass and Arapahoe Basin ski area as well, where the fixed sensors allow managers to measure every 10 centimeters of new snow and even slab thickness after a storm.

Private companies are supplying high-resolution satellite imagery as well, albeit with a price tag that’s beyond the budget of most avalanche forecasting centers. 

Planet, one of the largest private satellite imagery companies, employs more than 130 satellites to provide clients with 3- to 5-meter resolution images, according to the company’s website. Clients can choose what geographic region they want covered, at what frequency — up to multiple times a day — and for how long a period.

Such rich data would no doubt benefit mapping avalanches and filling out the avalanche record, Cooperstein said, adding that the cost of such services are becoming more affordable.

In Colorado, field-based avalanche detection and forecasting — in which avalanche forecasters scour the mountains on snowmobiles and skis in search of the most unstable snowpack — aren’t going away any time soon. While these technologies are exciting, most aren’t operational, or simply cost too much for widespread use in Colorado’s diverse and wide-ranging backcountry. 

“LiDAR and radar and camera technologies from ground-based or drone-based platforms, I think we’ll see those in increasing use for ski areas and highway departments who need real-time feedback on evolving conditions and the success of avalanche mitigation,” Deems said.

But the need for more avalanche-detection methods that are consistent from mountain range to mountain range and state to state remains if scientists and practitioners hope to better connect weather dynamics to avalanche activity, Deems added.

It may be key to planning for the future as well. Most mountain areas lack data-based projections of how climate will affect avalanche activity, because avalanche datasets are full of big holes, Eckerstorfer, the NORCE researcher, said. The sooner these datasets are filled in, the sooner plans can be formed to mitigate avalanches in a changing climate. 

“If you live in a mountain environment, you need to start preparing now for what’s to come in a couple of decades,” Eckerstorfer said.


A final Colorado Avalanche Information Center report on the slide released Sunday provides details on the deadliest Colorado avalanche since 2013 capping a week where 15 backcountry travelers have died in slides across the U.S.

Jason Blevins

Feb 8, 2021

The San Juan County Search and Rescue team that recovered the skiers included a county commissioner, a town councilman, business owners, local avalanche experts and other residents of Silverton. (Provided by San Juan County SAR) 

Communication challenges in a large group and a “terrain trap” were contributing factors in the deadliest avalanche in the state since 2013, according to the Colorado Avalanche Information Center’s report on the massive slide that killed three men near Ophir Pass in the San Juans on Feb. 1. 

A skier who was buried but survived the avalanche on South Lookout Peak near Silverton that killed three of his friends described the torrent of snow that engulfed him like “a river.”

“I was fully under snow for approximately 15 to 25 seconds,” the unnamed skier told investigators with the Colorado Avalanche Information Center, which issued its final report on the deadly avalanche on Sunday.

The report described the challenge of moving a large group — this one was seven skiers — through avalanche terrain as well as how “small communication errors and misunderstandings can be amplified in large groups.” 

The report comes after the deadliest week for avalanches in the United States in more than a century. Counting this South Lookout Mountain tragedy and a slide in Utah’s Millcreek Canyon on Saturday that killed four, 15 people have died in avalanches in the country in the last seven days. 

Three men — Adam Palmer, Seth Bossung and Andy Jessen — were buried and killed in the avalanche. They were among a group of Eagle County locals visiting the Opus Hut. The crew had been skiing in the backcountry around Red Mountain Pass and skied out of Silverton Mountain’s helicopter on Sunday. They skied into the Opus Hut around 1 p.m. on Monday and spent about an hour at the remote cabin before venturing out for an afternoon tour. 

Some of the skiers, like Palmer, had been part of the annual trip to Opus for many years. Others, like Jessen, were new to the trip. All were friends from back home in Eagle. As they left the hut, the caretaker said there had been “lots of [avalanche] activity on all aspects and today is the warmest day since December,” according to the report by CAIC forecasters Spencer Logan, Jeff Davis, Rebecca Hodgetts and Mike Barney.

The crew climbed a short stretch and skied a southwest-facing slope into the drainage between Ophir Pass road — which is closed in winter — and The Nose, a descent on the skier’s left of South Lookout Peak.  They climbed to a ridge toward the top of the The Nose and stopped at a saddle around 11,800 feet. They decided to ski a sparsely treed slope and skied one at a time with a plan to regroup on a small knob just above a steep-walled gully at the bottom of the peak’s face.

“Before the entire group collected on the knob, the first skiers to arrive began skiing down the rest of the slope and into the gully,” reads the report. 

Palmer, Jessen, Bossup and the unnamed fourth man descended the gully, which the report describes as a “terrain trap.” One of them stopped on the right wall of the gully and the fourth skier yelled for him to avoid the steep section of the gully on the right side. All four men were moving down the gully when the avalanche released around 3:20 p.m.

The report says the avalanche came in two waves. The fourth skier was able to pull his avalanche airbag when the first wall of snow released and he was standing in the bottom of the gully when a second wave hit him from behind. 

“He was engulfed in snow and tumbled violently,” the report says. 

The remaining three skiers were able to find the fourth man, whose airbag was visible above the debris. Palmer, Jessen and Bossung, however, were completely buried. 

The CAIC report details the accident in this Feb. 2 photograph. The yellow line shows the group’s route to the knob before descending into the gully. The avalanche outlined in red was triggered by the skiers descending the gully. Avalanches that ran sympathetically are noted in in green and brown. Blue circles indicate the approximate burial locations of the four skiers. The large avalanche to the looker’s left of the fatal avalanche was triggered by explosives to protect searchers. (Provided by the Colorado Avalanche Information Center)

The four skiers sent an SOS signal on an InReach device around 4:40 p.m. and they were able to detect signals from their friend’s avalanche transceivers. But the closest signals they could detect on their transceivers were between 4 and 5 meters, or about 13 to 16 feet. (For transceiver searching, the digging begins at the lowest reading, which is the closest point to the buried skier.) The four men dug for two hours.

Inside the holes, the signals from the transceivers showed their friends still 5-to-6 feet below. They were able to touch one of their friends with a probe pole from within one hole.

At nightfall, the four men were exhausted and made the “difficult decision” to return to the hut, reads the report. They built snowshoes out of tree branches for the fourth skier who lost his skis in the slide. Around 7:30 p.m. they made contact with San Juan County Search and Rescue members who had organized around 5 p.m. after getting the group’s distress call. The rescuers brought the four men back to the trailhead and suspended search operations until the following morning. 

Searchers recovered two of the men on Tuesday as the Helitrax helicopter operation dropped explosives onto adjacent slopes, triggering several large avalanches. The search team of more than 30 people returned on Wednesday and recovered the third skier. One of the men was buried 9 feet deep. Another was at 11 feet. And the third was buried 20 feet deep in the gully. 

Search teams broke eight shovels and used chainsaws to cut through the cement-like snow to reach the men. 

Looking down the gully where three Eagle County men were killed in an avalanche near Ophir Pass on Feb. 1. (Provided by the Colorado Avalanche Information Center) 

The Colorado Avalanche Information Center provides comments on all its fatal accident reports, hoping that insight into the events leading up to the avalanche can help other backcountry travelers avoid getting caught in a slide. 

Ethan Greene, the director of the Colorado Avalanche Information Center, describes his reports as akin to a newspaper. There are the news reports and the editorial section. In this avalanche, the forecasters highlighted the difficulty in communicating with a large group. Four of the skiers began their descent of the gully before the rest of the skiers arrived at the knob. 

“Yet Rider 1 started down the gully before the rest of the group arrived,” the report says. “He was quickly followed by Riders 2, 3 and 4. There were suddenly four riders in the gully, all out of sight of the people on the knob when the avalanche released.”

“Gullies are bad places to be,” Greene said in an interview Sunday. “A lot of guides and avalanche professionals just avoid them altogether.”

Greene said his staff can’t point to the communication breakdown as a cause for the accident “but it’s definitely something that came out of the discussion that staff had with the people in the group.”

Greene and his team have been working hard this season, which has seen eight people buried and killed in Colorado avalanches, with more winter to come. 

A weak layer of snow buried deep in the snowpack is shedding slabs of new snow. As more snow falls, the stress on that weak layer grows and avalanches hazards rise. 

This is not a normal year, Greene said, who estimates the increased avalanche danger this season is maybe a 1 in 10 occurrence. So, for a skier who has spent 20 years in the Colorado backcountry, this is likely the second time to see this level of widespread avalanche hazard. 

“This is the year to keep things mellow,” Greene said. “This is frustrating for us. Obviously we are not doing enough, but we have been doing everything we normally do plus an incredible amount more. It’s hard to know how successful we are. Maybe if we were not doing what we are doing, things would be worse. But eight people dead by the first week of February — this is not a good place to be.”


Events Leading to the Avalanche

On Monday, February 1 a group of seven friends met in Silverton for a multi-day trip to a backcountry hut east of Ophir Pass. They ranged in age from mid 30s to mid 50s. Some had been backcountry skiing together for many years, while others were new additions to the group. Several of them had made annual trips into this hut for at least ten years. Four members of the group had been in the area since Friday skiing in the backcountry and with a local helicopter skiing operation. Three members of the group arrived Sunday evening.

The group left Silverton around 10:30 AM and drove to the winter closure of CR8 (Ophir Pass Rd). At the trailhead the group checked transceivers and discussed avalanche conditions. They left the trailhead around 11:30 AM. They identified the south-facing slopes above CR8 as a potential avalanche hazard and traveled one at a time below them to reduce their exposure. They arrived at the hut around 1:00 PM and spent about an hour there before heading out for an afternoon tour.

The group discussed assessing avalanche conditions on a terrain feature known as The Nose, which is between Crystal Lake and the Middle Fork of Mineral Creek. On previous trips they had skied this slope, but did not plan to ski it that afternoon. Before leaving the hut they talked with the hut keeper who said there had been “lots of [avalanche] activity on all aspects, and today is the warmest day since December.”

They left the hut and climbed a short distance before descending a southwest-facing slope into the drainage between CR8 and The Nose.They climbed a gentle ridge to the south heading towards The Nose.They reached a small saddle at about 11,800 feet, and decided to descend a northeast facing, sparsely treed slope. The group rode down one at a time and started to regroup on a knob just above a steep-walled gully at the bottom of the slope. Before the entire group collected on the knob, the first skiers to arrive began skiing down the rest of the slope, and into the gully towards the Middle Fork of Mineral Creek.

Accident Summary

Rider 1 skied down from the knob and into the gully. Riders 2 and 3 followed the same path, skiing close to each other. While Rider 2 continued down the gully, Rider 3 stopped along the skier’s right wall. Rider 4 slid over the convex roll at the gully entrance to yell down, telling Rider 3 to move to the left side of the gully and avoid the steeper slopes on the right. All four were moving down the gully when the avalanche released at about 3:20 PM.

The avalanche caught Riders 1, 2, 3, and 4. Rider 4 described the avalanche as two waves. The first wave slowly pulled him into the gully, but he was able to stay on his feet. Thinking there was enough snow to bury him if he fell over, he deployed the avalanche airbag on his backpack. After the snow stopped he was standing in the gully. Seconds later a larger wave of snow hit him from behind. Rider 4 immediately lost his skis and poles. He was engulfed in snow and tumbled violently. “It felt like I was in a river and I was fully under the snow for approximately 15 to 25 seconds” Rider 4 explained, and was “moving very fast a significant way down the gully”. When the avalanche stopped, Rider 4 was buried in the debris with his head under the snow, but a portion of his airbag was visible on the surface (partially buried-critical). Riders 1, 2, and 3 were completely buried in the avalanche debris.


All of the fatal avalanche accidents we investigate are tragic events. We do our best to describe each one to help the people involved and the community as a whole better understand factors that may have contributed to the outcome. We offer these comments in the hope that it will help people avoid future avalanche accidents.

Moving a large group through avalanche terrain one at a time requires considerable time and careful coordination. Small communication errors and misunderstandings can be amplified in large groups. This challenge may have played a role in this accident. Some of the party expected everyone to regroup on the knob above the gully, yet Rider 1 started down the gully before the rest of the group arrived. He was quickly followed by Riders 2, 3, and 4. There were suddenly four riders in the gully, all out of sight of the people on the knob when the avalanche released.

The avalanche caught the four riders in a narrow gully where debris piled up extremely deep. Rider 4’s position higher in the gully, staying more skier’s left, and his airbag likely all reduced his burial depth. The others were not as lucky, and were deeply buried. In a terrain trap like this gully, the depth of avalanche debris can vary dramatically over a very small distance.

Digging a person out of avalanche debris is by far the most time consuming portion of a rescue. Deep burials are very difficult for a small team to manage. The debris is almost always very hard. Equipment breaks, people tire quickly, and just managing the snow you are removing becomes a monumental task. The four riders worked for hours and only got through the top half of avalanche debris above the victims. Anyone who has dealt with avalanche debris over a few feet deep will tell you the digging gets more difficult and more complicated the deeper you go. Eventually it took an organized search and rescue group, with many people and power tools, two days to recover all three riders.

The group and search and rescue personnel both detected two transceiver signals in close proximity at one of the burial sites. This led them to believe that Riders 2 and 3 were buried very near each other. They eventually determined the signal came from a single avalanche transceiver that was over 10 years old. Over the last 10 years the standards for avalanche rescue transceivers have improved. Although not common, modern transceivers can sometimes recognize the signal from certain old transceivers as two signals, a primary and ghost signal. In this case the age of the skier’s rescue device did not play a significant role in the outcome of the accident. However, it is a good reminder to make sure you understand the performance of the equipment you and your partners are using. Most avalanche rescue organizations and transceiver manufacturers recommend retiring devices that are more than 10 years old.

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