The Next Storm

If you are in the mountains today consider yourself blessed.  It will surely be the most beautiful morning of the season so far with clearing skies and a fresh coat of new snow.   The view from Snowbird at sunrise is spectacular.

Observations from Alta-Collins indicate 2 inches of snow overnight and a storm total of 16 inches, bringing the total depth to 21 inches.  Snowpack water equivalent at the Snowbird SNOTEL sits very near 3 inches.  

High clouds will, however, be moving in this afternoon in advance of the next storm system.  The weak surface front associated with that system is forecast by the GFS to move into the Salt Lake Valley early Thursday morning and bring a period of unstable, moist, west-northwesterly flow.

Below is our GFS-derived forecast guidance for Little Cottonwood Canyon showing the bulk of the precipitation at Alta mainly from 5 AM Thursday morning to 6 PM Thursday afternoon.  During that period, the GFS produces about 0.4 inches of water and 6 inches of low density snow with snow-to-liquid ratios of around 15-17 to 1.  

Given the cold conditions and northwesterly flow, there is also potential for lake effect.  Odds are best Thursday morning when the moisture is deepest.  Given the west-northwesterly flow, our GFS-based algorithms give the best chance to the Bountiful area.  

Of course, the GFS is just one model.  The ECMWF has about 0.25" of water equivalent in the upper Cottonwoods and, consistent with our lake-effect product above puts the heaviest precipitation (just over 0.5") just north of the Salt Lake County/Davis County line in the Bountiful Area mountains.  

On the other hand, the 12Z HRRR has a bit of a different idea.  It generates about 0.2-0.25" of water equivalent in the central Wasatch, but a lake band further west extending into the northern Oquirrhs where precipitation is heaviest. 

These are the joys of forecasting post-frontal instability showers.  I'm going to go for 4-8" at Alta-Collins for tonight through Thursday afternoon and will be praying for more.  You should too.