Email exchange with NWS forecaster (Grand Junction office) Joe Ramey
Monsoon: well its always tricky isn’t it? We often say oh the monsoon started last week. Last year was the exception when the climate signals were picking up on a wetter than normal summer by February or so. And it worked. This year…not so much. But now there are hints its on the horizon. The Phoenix office is using “monsoon” wording too.
Grand Junction NWS forecast discussion of Monsoon flow: LONG TERM…(Saturday night through Thursday)
This weekend the north enjoys a cool down of 5-8 degrees while the south will see little temperature change. Precipitable water values remain around 0.5 inch over the eastern San Juan mountains that may produce an isolated thunderstorm or two. For the new week a broad ridge rebuilds over the Great Basin then shifts subtly east later in the week. Deep subtropical moisture begins to pool over the Sonoran and Chihuahuan Deserts approaching 2 inch precip water values by Thursday. This moisture leaks into the Four Corners beginning Tuesday then deepens to around 1.2 inches by next Thursday. Increasing showers and thunderstorms can be expected starting Tuesday and favoring the south. But we are not ready to use the “M” word yet.
Phoenix NWS forecast discussion of Monsoonal flow.
Tuesday through Thursday…Model guidance including NAEFS and GEFS ensemble guidance is suggesting that our flow pattern is setting up in a standard monsoonal fashion, with the upper high migrating towards the vicinity of the four corners, and a much deeper and widespread southeast steering flow working its way over the AZ deserts and even into southeast CA. Moisture continues to work across the lower deserts and rainfall chances will increase with slight chances developing to the lower Colorado River valley and potentially into the deserts of southeast CA. We have raised POPs over much of the CWA correspondingly, with chance numbers over the higher terrain of southern Gila County and slight chances over much of the south central deserts westward. High temperatures take a slow decline day to day as humidity values rise.