Leap Day Snow!

Posted Saturday, February 29th, 2020 by Taylor McCorkle

Hope you all enjoyed an unseasonably warm day in the valley – the pre-storm environment brought in those typical strong southerly winds with a cloud deck blanketing northern Utah.

Forecast for Saturday evening – Monday:

The National Weather Service office in Salt Lake City has issued a Winter Weather Advisory that is currently in effect through Sunday at 10 PM.

Watches, warning and advisories – graphic from weather.gov/slc

This weekend’s disturbance is the result of a splitting trough that will make landfall in Northern California this evening. The southern portion of the split trough will then progress eastward, pushing a cold front through the area late tonight into tomorrow mid-day. Shown below is a GFS forecast of 500 mb heights and mean sea level pressure contours, valid tomorrow around 5pm. The black diagonal lines across Northern Utah represent a pressure gradient that will follow the cold front passage.

GFS forecast 500 mb heights (shaded) and mean sea level pressure (black contours) valid tomorrow at 5 pm. Forecast graphic via tropicaltidbits.com

Following the frontal passage, sub-freezing temperatures will penetrate to the valley floor, resulting in frozen precipitation at all elevations. After the frontal passage, winds gusts should substantially decrease, leaving behind rather quiescent conditions as we move into the afternoon hours. Early morning skiing may be a bit of a challenge with strong winds and potentially low visibility.

The GFS and NAM both agree on the timing of the cold front arrival – this will occur beginning around 5 am tomorrow morning. As the cold front traverses Northern Utah, some mid-level instability could result in periods of heavy snow showers in the mid and high elevations of the Wasatch front. Below shows a time-height forecast of relative humidity (shaded colors), potential temperature (black lines), freezing level (blue line) and instability (red contours). Wind barbs are also shown. Remember, with these plots, time goes from left to right on the x-axis.

NAM 12 km time height cross-section showing forecasted relative humidity, instability, freezing level, and wine at various levels. Plot via weather.utah.edu.

One unique aspect of this storm is that as it progresses, we will not see that predominate northwest wind shift like we do in typical troughs. This is due to the splitting nature of the trough that I mentioned earlier.

This storm isn’t expected to be huge, but it will bring several inches of fresh snow to the Wasatch, which is desperately needed after this dry stretch we have experienced. I feel confident in forecasting a storm total of 6-10″ for the Cottonwoods and 3-5″ for the Park City area.

Not a bad start to March in my opinion.

Enjoy the rest of the weekend!
-Taylor

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