A Parade of Storms

Posted Wednesday, February 27th, 2019 by Taylor McCorkle

TLDR: A series of disturbances will make their way through the Intermountain West beginning tonight and lasting through the weekend. Plenty of snow chances to be had, but exact details remain uncertain, especially with increasing lead time.


A weak disturbance brought some rain to the valley earlier today and dropped a few inches of snow in the mountains. Currently, Snowbird is reporting 4″ of new snow. This brings the season total up to a whopping 444″.

Short-Term Forecast:
Not much has changed in the way of storm progression through the weekend. Here’s a quick update on our thoughts through the weekend.

Currently, the upper-level low I mentioned yesterday is still sitting off the coast of the PNW.  As it moves eastward, it will begin to eject weak disturbances that could bring us scattered precipitation over the next 24 hours or so.  A weak ridge will move into the area this evening, keeping precipitation to a minimum.

Tomorrow afternoon, expect precipitation chances to be on the rise as that upper-level low moves onshore. This dynamic feature will interact with a strong 700 mb (crest level) temperature gradient, enhancing the snowfall in Northern Utah and the mountains. As the weekend progresses, a second surface low, currently situated over the central and southern Pacific, will move onshore.  The greatest impacts from this storm will be felt in central and southern Utah.  The latest GFS forecast of 500 mb heights and mean sea-level pressure is shown below. Valid through noon Sunday.

18Z GFS forecast of 500 mb heights and MSLP courtesy of tropicaltidbits.com
18Z GFS forecast of 500 mb heights and MSLP courtesy of tropicaltidbits.com

As mentioned yesterday, the track of these low pressure features will greatly impact the snow accumulation distribution across the state.  Given the current information, snow forecasts remain similar to yesterday.  Here is an accumulation forecast from the 12Z NAEFS ensemble at Alta Collins.. A bit of bifurcation has occurred between the GEFS and CMCE members, but the mean is still consistent with what we have seen all week. This is likely an overestimation, but still exciting to see.

12Z NAEFS ensemble forecasts of snow accumulations at Alta.  Plot courtesy of weather.utah.edu
12Z NAEFS ensemble forecasts of snow accumulations at Alta. Plot courtesy of weather.utah.edu 

In contrast, the European model which is a bit more down to Earth, is forecasting ~15-20″ for the Cottonwoods through Sunday.  I think this is a good estimate, but perhaps a bit conservative as the snow ratio is only set to 10:1.  If you are familiar with snow ratios, then you know it isn’t uncommon for us to get low-density snow.  Low density snow in the Wasatch can result in 15:1 or even 20:1 snow ratios, which would allow for greater accumulations.

12 Z ECMWF forecasted snowfall through Sunday evening. Courtesy of models.weatherbell.com
12 Z ECMWF forecasted snowfall through Sunday evening. Courtesy of models.weatherbell.com

All in all, it looks like another stellar weekend is on tap.
Enjoy!

-Taylor

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