March Means More Winter

Posted Tuesday, February 26th, 2019 by Taylor McCorkle

As a particularly deep February comes to a close, we can look ahead to March with excitement and anticipation.. Winter isn’t over yet.  As we progress through the work week, Utah will be impacted by several systems beginning Wednesday and lasting into the weekend.  As Pete mentioned yesterday, an upper-level trough will impact northern Utah on Thursday into Friday, closely followed by a system that will bring the largest snow accumulations to central and southern Utah.


Overview:
An upper-level low is currently sitting off the Pacific Northwest Coast, as shown by the GOES-West imagery, provided by the CSU CIRA site. This low pressure system has ample moisture available, which could bring late-week powder to the Northern Wasatch.

GOES-West visible satellite imagery via CIRA
GOES-West visible satellite imagery via CIRA

As this upper-level low moves west, it will eject across Utah and create several smaller short-wave disturbances.

Short-Range Forecast:
Beginning tomorrow and lasting through the work week, snow chances will be on the rise throughout Northern Utah. Prior to the arrival of the main trough on Thursday evening, a stream of moisture will interact with the front side of the disturbance, allowing for some snow accumulations to potentially occur on Wednesday (Labeled 1 on figure below). This will be before the cold front arrives, so snow levels will remain elevated.

NAM 12km Time-Height cross-section via weather.utah.edu
NAM 12km Time-Height cross-section via weather.utah.edu

The trough that is currently located over the PNW will finally move into the area on Thursday, bringing along with it plenty of moisture and lift that will be required for significant snowfall (labeled 2 on plot). The cold frontal passage wont actually occur until the early morning hours on Friday where the black lines on the plot become vertical and the freezing line (thick blue line) trends toward the bottom of the plot, which signifies the valley floor. Snowfall should continue through Friday.

After Friday, some uncertainty arises given the timing and amount of additional snowfall that northern Utah will receive.  Some short wave activity and additional enhancement from orographic lift could provide prolonged periods of snowfall, especially when the wind shifts to the northwest.  Another source of snowfall could be the low that is set to impact central and southern Utah.  Depending on its track, northern Utah could sneak a few extra inches in before its all said and done.

Below is a forecast graphic of Mean Sea Level Pressure and 6-hr precip from the 12Z GFS.  Model forecast graphic and gif produced by Tropical Tidbits

GFS MSLP and 6-hr precip valid 5 pm Tuesday through 5 pm Friday
GFS MSLP and 6-hr precip valid 5 pm Tuesday through 5 pm Friday

So how much snow are we looking at? Ensemble solutions are still varied with some members showing a few inches, and others going bananas with up to 40″ through the end of the week. Below is an accumulated snow graphic from the SREF Ensemble for Alta. The model experiences significant bifurcation between its two dynamical cores, but I wanted to post it to show timing of the various systems. Additionally, I think the ensemble mean (dark blue line) is actually somewhat useful as it is close to solutions from other modeling systems.

09Z SREF Ensemble via weather.utah.edu
09Z SREF Ensemble via weather.utah.edu

Snow Totals:
Through Friday, northern Utah will experience snowfall attributed to several different atmospheric features. The uncertainty and interaction among these features is what is causing the spread in model solutions, as you saw in the SREF plot above. Given what we know today, here are my thoughts on snowfall through Friday:
Cottonwoods: 16-22″
Ogden/N.Wasatch: 14-20″
Park City area: 12-18″
Central Utah: 5-9″
Southern Utah: 8-14″

As I mentioned, this is a complex set-up, so the forecast will likely change between now and Friday. Check back with us for the latest.

Have a great week!

-Taylor

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