A Major Winter Storm Impacts the West This Week

Let me begin by welcoming those interested in weather in the West, outdoor and ski enthusiasts, and the curious, to my new blog. This is my first blog post, so there will be some trial and error while I improve my content. If you want to know more about me, please read my "about me" bio section. I plan to post when there's interesting weather around the West, with a special focus on Utah and the Wasatch Front, where I live. During storms, I may post "updates" to my blog as things evolve. These will be my opinions, sometimes in collaboration with other weather groups. Official forecasts and statements can be found at weather.gov/

So, let's jump into some weather discussion as the pattern over the Western U.S. has become quite active. Satellite imagery shows a deep trough centered over the Pacific Northwest with individual storms rotating around this region into CA and the interior. In fact, this is one of the coldest storm systems in many years for some locations. It's also huge, impacting the entire West from the CA/Northwest Coast to the Rockies, well into the New Year. If you're traveling this week, please check road conditions! So how cold is this system? Take a look at the snow falling across the Pacific Northwest lowlands this morning, including Seattle and Portland. Currently (9:30 am PDT), Seattle has moderate snow and the temperature has fallen to 25 F with around one inch on the ground at Sea-Tac. Even crazier, Fraser River outflow is creating near blizzard conditions from Bellingham north to near Vancouver, Canada. Temperatures are in the teens, winds are gusting over 40 mph, heavy snow is falling, and visibility is poor. Wind chills are currently below -10F in the Bellingham vicinity. More snow and cold is on the way too, spreading into the Great Basin and Rockies, including Utah. Heads up folks! 

So how will all this affect Utah? Well, we got a small taste of winter along the Wasatch Front this morning as temperatures fell into the lower 30's and we finally got some modest snowfall. A strong squall associated with colder air moved through the I-15 metro corridor for a couple hours, during the morning. Gusty winds and heavy snow briefly fell, leaving a dusting to around 1" in the valleys. The mild air mass overnight that preceded this system led to enough instability for thundersnow, yep-- you heard that right! There were several strikes along the squall line this morning, just as we had with our last heavy snowfall. Take a look.

Today's snow tapered off quickly, but we have a couple more storms to watch this week. Unfortunately, we have suffered from a lot of southwest flow aloft, which really limits snowfall potential in some mountains and valleys, especially the Salt Lake Valley. A storm arriving late Monday afternoon will be slow to kick in with this less than ideal flow pattern. But models do show a window Monday night where the flow turns more west to west-northwest. This will give us slightly better accumulations in the valleys and mountains. Here's the 24 hour snowfall blended model forecast. Roughly, 1-2" accumulations in the valleys, slightly more on the benches, and maybe a foot in our northern mountains. Some lake effect enhancement could occur from Bountiful to Ogden as well, producing locally higher amounts. *6pm MDT Update: temperatures will fall into the 20's by early Tuesday evening. Kuchera snow ratios work well in that case, and boost valley amounts by about 1". So, perhaps 2-3" is possible in the SL Valley. Perhaps double this amount benches and Davis county due to lake enhancement. Mountains get over 1 foot given the flow and higher ratios taken into account. 

With the likelihood of some snow on the ground, radiative cooling, and 700 mb temperatures near -20C (varies but roughly 10,000 ft above sea-level), the coldest temperatures in a couple years are expected. Daytime highs along the Wasatch front will only reach the 20s with lows plummeting to the lower teens or even single digits in the outer metro areas. Outlying cold pocket valleys could drop close to zero F, that's you Park City! Here's the SLC temperature outlook through Thursday morning.

The most promising storm this week is on track to arrive around Friday. This storm has one main difference, as models show a period of cold unstable northwest flow aloft. Check out the GFS 700 mb wind direction below! A much more favorable pattern for higher snow amounts in the Salt Lake Valley and most mountains. It's too soon to speculate on amounts as slight changes in the track could lead to less snow. At this time, it does look like the best potential snow producer of the week. Just look at the 500 mb trough anomaly over our region, impressive!