Winter is Coming

I've been waiting all season to say that, but the models are trending and trending in a way that it may actually snow, not only in the mountains, but even, dare I say it, at low elevations. 

Let's break things down into pieces.  I'll use the Euro and hit some of the highlights.  Overnight tonight, a strong mid-level cold front pushes through northern Utah, bringing our first round of precipitation in the form of mountain snow and valley rain.  This front is the band of heavy precipitation extending from SW Wyoming through central Utah and Arizona in the Euro forecast below valid 0900 UTC (0200 MST) tonight.  

In the way of that front, moist, unstable southwesterly flow predominates late tonight, tomorrow, and tomorrow night with periods of mountain snow and snow levels near the valley floor, although official NWS forecasts are for less than an inch through Tuesday night at the lowest elevations of the Salt Lake Valley and a bit more on the benches.  

Wednesday looks like the best storm of the season for the valleys (something else I've wanted to say for a while, although we've had all of 0.1" at the airport so far!).  The Euro (and other models) has a cold front moving through Wednesday morning bringing snow to all elevations.  

I've been busy planning for our field campaign today so lack the time for a proper deep dive on snowfall amounts.  I encourage you to look monitor official forecasts and drive slowly on snow covered roads when they finally appear.  

Mother Nature Is About to Release the Hounds

Today is probably going to be the quietist of this work week.  For the most part, it is dry, although if you peer to the west from the University of Utah, you can still see some of our dendritic friends are still falling over the Oquirrhs.  

Cams from the central Wasatch also show some flakes falling, although it's not adding up to much.  

Source: Alta Ski Area

This is what constitutes a break in our current storm cycle.  It will persist through tomorrow morning, and then Mother Nature will release the hounds.  It doesn't matter what elevation you live at in northern Utah, you are going to be experiencing significant snows through the weekend.  

Let's get to it.  First, the GFS forecast calls for a frontal system to be moving across northern Utah by 0000 UTC 10 January (5 PM Tuesday.  

It is likely that this will bring all-elevation snow to northern Utah for the evening rush hour and significant snows overnight for the mountains and the Salt Lake Valley.  As such, the National Weather Service has issued a Winter Storm Watch for much of the Wasatch Front and the mountain valleys.

Tomorrow will be a good day to monitor forecasts and consider an early departure from work if appropriate.  This is a storm that will likely affect the northern Wasatch Front earlier and eventually the southern Wasatch Front.  

That's all fine and dandy, but how about we do it again on Wednesday?  Sure thing.  The GFS brings another frontal system in by 0000 UTC 11 January (5 PM Wednesday).  

Then, for the skiers, how about some unstable northwesterly flow on Thursday.

In general, there is good agreement between the GFS and the ECMWF models through Thursday.  Thus, I'll be bold and share the GFS-derived time series for Alta.  Now don't look ahead.  Do not peak beyond 5 PM Thursday. I repeat.  Do not peak beyond 5 PM Thursday.  Through 5 PM Thursday the GFS is putting out 1.58" of water and 23.4" of mostly low-density snow.  The system tomorrow afternoon may produce some higher density snow to start, afterwhich snow to liquid ratios flctuate between 13:1 and 20:1.  

By and large, this period looks locked and loaded for 20–30 inches at Alta from tomorrow afternoon through 5 PM Thursday, although I confess that I want to say "possibly more."  Much will depend on what occurs during the post-frontal period on Wednesday night and Thursday.  

Now you can look beyond 5 PM Thursday.  Holy cow!  If you want to push the backcountry snowpack to the breaking point, the GFS forecast for the weekend might do it.  At 0000 UTC 14 January (5 PM Saturday) it puts a beast of an upper-level trough and frontal system over the Pacific Northwest.  Utah is at the tip of an atmospheric river with strong, moist, crest-level flow.  

Eventually that trough and it's cold front come through by 1200 UTC 14 January (5 AM Sunday).  It's a monster system, with screaming winds, abundant moisture, and a hell of a punch.  

Little wonder that the GFS is putting out more than 4" of water and 60 inches of snow for Alta-Collins through Monday per the time series above.

That is, however, a fairly extended forecast, so let's look at a few other models.  One is the ECMWF. For 1200 UTC 14 January (5 AM Sunday), it actually has a somewhat similar forecast, but the trough is a tad slower and less intense.  We would still see significant snow, but the crest-level winds might not be as strong.  

Looking at the downscaled NAEFS, nearly all of the members are pretty jacked for the period through 15 January.  The mean water equivalent for Alta is 5 inches and the lowest amount is just over 2.5 inches.  

The bottom line is that Mother Nature is going to release the hounds.  This looks like an incredibly active storm period.  It is essential to monitor forecasts (details do change), not just for the mountains but also the valleys, and avalanche forecasts.  Be respectful of resort and backcountry closures and give our friends in the snow-safety community your support.  The weak snowpack that currently exists is going to get a serious stressing.