Sunday, October 24, 2021

Sunday Forecast Update

Not much change from yesterday's forecasts except for a skiff of precip later today and a bit later cold-front arrival tomorrow evening.  Below his this morning's (Sunday) 12Z Sunday GFS-derived forecast for ltitle Cottonowood.  Temperatures on Mt. Baldy climb to > 35˚F through tonight and remain warm through tomorrow.  There's a bit of precipitation associated with a weak-warm-front-like feature moving through this afternoon.  The GFS generates about 0.16" of water at Alta Collins and just about a half inch of snow due to snow changing to rain during the passage of the feature, even at 9700 feet.  

The GFS continues to keep things mainly dry until the approach of the cold front Monday evening.  That's when temperatures and snow levels drop and precipitation gets going.  Expect snow levels to fall pretty rapidly and, perhaps after a bit of rain to start, the event to be mainly snow at upper elevations with snow levels eventually falling to below 6000 feet by Tuesday morning.  The GFS is still pretty excited for water totals (~2") and snowfall totals (~20") at Alta-Collins during and following the frontal passage.  Those totals are for late Monday through Wednesday morning and include the skiff of precipitation this afternoon and the cold frontal and post-frontal precipitation.

The GFS is very close to the downscaled SREF mean water equivalent and snowfall for Alta Collins.  The SREF has most members has a supermajority of members generating 1.5 to 2.5 inches of water (including a bit this afternoon) and 15 to 25 inches of snow.  Take a smidge off of those for the frontal and post-frontal period. 

If, however, you are like me and believe the key to a happy life is low expectations, then look to the ECMWF model which is on the lower end with about 1.5 inches. 

By and large, things continue to look good for a big dump.  With high wind and precipitation rates, rising avalanche danger is likely, including at the resorts which are still de facto backcountry.  I have been wondering if Alta might close to uphill to do some avy work, but nothing yet on their site suggesting this.  Please post below if you hear anything.  

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