The arrival

Wednesday, September 25, 2013 at 6:57 am

Wednesday AM:

After much anticipation over the past 2+ weeks, the first storm likely to bring snow to the Wasatch is on our doorstep.  Cold front and associated winds are moving into Northern Utah as I type this.  Precipitation will likely develop along and directly behind the front later today.  Models aren’t indicating too much precip with the front but with it’s slow movement, I wouldn’t be surprised to see some banding of precipitation that could lead to higher amounts in specific areas.  Snow levels for most of today will run high, up to 10k feet this afternoon, dropping to 8k feet behind the front this evening as precipitation dwindles, therefore, I don’t expect much more than a dusting on the peaks today.

It looks like behind the initial frontal push today, there will be a break in precip tonight into tomorrow morning.  A secondary wave will move into the region tomorrow night as the trough fully drops into the Great Basin.  This secondary wave will be much colder and will generate good orographic lift in the mountains (especially areas favored by northwest flow).  The other factor will be the potential for lake effect snowfall.  Generally, lake effect requires even colder systems, but given that it is still September and the lake is quite warm, it doesn’t take as much to generate the necessary temperature differential.  Areas south and southeast of the lake could see lake enhancement or lake banding on Thursday night.  Snow levels will continue to fall down below 6K feet by Thursday night.  That means that mountain valleys (PC, Heber, etc), should see some snowfall.

Snowfall amounts are difficult to forecast.   This system’s snowfall potential is almost entirely dependent on the cold pool portion of the storm and generating good orographics.  As some of you may know from last year, orographics are responsible for the vast majority of snowfall in the Wasatch, especially areas like the Cottonwoods.  At the same time, relying on orographic lift can be tricky to forecast, especially this early in the season.

I think generally the Wasatch above 7K feet will see anywhere between 1-6″ by Friday evening.  There is, however, the potential for more than that, especially in areas that get under a good lake effect band.  We’ll be watching closely on Thursday night to see if and where these bands develop.

Looking beyond this storm… we dry out and start to warm up.  Models have come into consensus for a dirty ridge to keep us dry through early next week.  Models differ greatly later next week — GFS and GEM show ridging continuing with dry weather in Utah, ECMWF shows another deep trough digging into the west by next weekend (Oct 4-6).  Only time will tell which model has it right.  For now we’ll focus on the short-term …

Update tomorrow as the cold portion of the storm enters the region . . .

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