Buckle Up

 Red sky at morning sailors take warning?

Actually, the sky looked sort of purple today, as if I woke up in Mordor.  I knew something was up when I woke in the night and the house was shaking.  Indeed it was an impressively windy night in the lowlands with several sites reporting gusts of 60 mph or more including 68 mph near Point of the Mountain and 65 at the intersection of I-80 and SR-201 in the Salt Lake Valley.  

The instigator of this big blow is a deep upper-level trough that is amplifying off the Pacific coast.  The interaction of this feature with the Sierra Nevada is resulting in the development of low pressure over the Great Basin and a strong pressure gradient over western Utah.  

I'm a little surprised it blew so hard last night based solely on the large-scale analyses, suggesting something else is happening, but my time is limited for proper sleuthing and I'm more interested in the potential for snow.  

The upper-level trough note above, along with surface features that develop over the Great Basin as that trough digs off the west coast and eventually moves eastward, will dominate our weather over the next few days.  

Today in the Salt Lake Valley it will be dry, warm, and windy.  In the central Wasatch, there could be a few angry fits and starts of snow, but if it happens, it will only be enough to lacerate your face.  

A sharp surface trough and frontal boundary will develop just to our north (annotated on the upper-right hand image below).  This is a common occurrence as an upper-level trough digs off the west coast.  By 0600 UTC 8 Nov (11 PM MST Monday), the frontal boundary is just to our north, which is why we are likely to remain dry despite the fact that weak atmospheric river conditions extend over our area (lower right). 

On Monday night and Tuesday morning, that frontal boundary sags southward and at 1800 UTC 8 November (11 AM Tuesday) it's located very near the Salt Lake City International Airport.  

It's such a close call that I'm not sure if the front and it's precipitation will make it into the Salt Lake Valley and the central Wasatch.  Right now the GFS is bringing it right to the Salt Lake City International Airport.  Below is a closeup at 1800 UTC 8 November (11 AM Tuesday) and the wind shift is perhaps just north of the airport with light precipitation extending eastward to the central Wasatch.  

Right now, this is a chance of valley showers, mountain snow showers situation for tomorrow, with snow levels near or around 7000 to 7500 feet.  We'll potentially get skunked if the front stays a bit north, or do better if it pushes a bit farther south.  

Things begin to light up, however, as the upper-level trough and associated surface low move inland.  Rain moves into northern Utah Tuesday night and by 1200 UTC 9 November (5 AM Wednesday) a band of heavy precipitation covers most of western and northern Utah.  

For that storm period, the GFS has been bouncing around the past several runs between 2 and 4 inches of snow water equivalent for Alta.  In the latest run from last night, it's putting out about 0.3" with the cold front on Tuesday and then about 1.45" with the main band on Tuesday night and Wednesday, followed by some more dribs and drabs Wednesday night.  

A glance at the Euro suggests it's a bit wetter.  For the entire period, the downscaled NAEFS is putting out an average of about 2.75 inches of water.  All but two members are above 1.5 inches.  

The bottom line is that this will be another major storm adding 1.5 inches of water or more to our upper-elevation snowpack in Little Cottonwood.  Perhaps we will take a closer look tomorrow if I can find the time.