Models show a significant weather change with several waves of low pressure storms hitting late Wednesday into Thursday/early Friday for the San Juans with a potential 6-10″ inches of snow & possibly more above TL on SW aspects (see OpenSnow forecast below) followed by colder temperatures. Saturday another disturbance with northern flow and a few more inches are possible but will favor mountains north of the San Juans.
Although the blocking high pressure ridge that has been with us since mid-Oct will return, it temporarly retrogrades to the west allowing periods of unsettled weather into the New Year. The winds should also clear out the California smoke that has been putting a haze on our mountains the past few days.
The first storm will bring snow to all mountains as flow aloft swings to west-southwest as a strong Pacific trough digs into the Great Basin bringing snow to our very dry mountains by late Wednesday into Thursday afternoon. Then late Friday/early Saturday an approaching Arctic cold front rips into Colorado and will bring more snow, but favoring the northern & central mountains. The north San Juans might get a few inches, maybe more.
The National Weather Service said, “The energy with this strong compact storm, and the fact that snow ratios will be sky-rocketing behind the cold front, suggests this storm will likely have some curve balls to throw at us.”
GFS – US – 500mb – Loop ~ 12/19 – 12/29
The University of Utah ensemble forecast (showing multiple versions of two models) presents this forecast for Red Mountain Pass. Below is the forecast for Red Mountain Pass, in the southern mountains. Maybe 6-15 inches from the Thursday storm and another 2-5 inches from the Saturday/Saturday night storm.
The forecast for December 30th is for a shift, where the high pressure moves northwest over Alaska, and this allows storms to likely move more directly from the Pacific Ocean into the western US and Canada.