Thursday, December 7, 2023

A Cold Storm Is Coming

If you are into cold, northwesterly flow snow, I have a treat for you. 

Today we are getting an appetizer of mountain snow showers and valley rain showers that won't add up to much, but it gets more exciting late tonight and early Friday morning when a cold trough drops into northern Utah.  The latest GFS puts the primary trough axis at 500 mb and associated unstable northwesterly flow at 700-mb over Utah by 1200 UTC 8 December (5 AM MST Friday).  

I hate to say this as I think it could be a jinx, but the pattern looks really great through the day on Friday with the northwesterly flow locked in as another embedded trough with a reinforcing shot of cold air moves into Utah by 0000 UTC 9 Dec (5 PM MST Friday).  

Through 11 PM MST Friday, the GFS is generating 18.9" of snow (about 2" of this is from today) with snow-to-liquid ratios generally near or above 15:1.  

The HRRR is a bit drier and has slightly lower snow-to-liquid ratios, but is still cranking out about 14".  

These northwesterly flow storms can be a bit of a crap shoot, but this one looks pretty likely.  The uncertainty here is with regards to whether or not we get some embedded lake effect and/or graupel, the latter which might lower snow-to-liquid ratios some and can happen if things get really unstable. That said, I like this one putting out 1–1.5 inches of water and 12-24" of snow for Alta Collins through Friday night.  

In the wake of the trough, Saturday is going to dawn quite cold.  Our GFS-derived forecast product for Little Cottonwood is calling for morning temps near zero at 11,000 ft and in the low single digits at 9700 feet. Bundle up.  

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