Probability of Powder: The Long and Short Term

Posted Monday, March 11th, 2019 by marcelcaron

TLDR: A mild air mass will give way to cold polar air and a moderate powder drop Tuesday night. Scroll down for an initial snowfall probability forecast.


One-Month Probability Forecast

It seems out of the norm that a series of big powder dumps isn’t in the extended forecast. One storm this week will be followed by a period of low chances for a powder day. The next month, however, may favor wetter-than-normal precipitation according to NOAA’s CPC climate outlook:

probability
The Climate Prediction Center’s one-month outlook for the probability of anomalous precipitation. Shaded are probabilities for above- (green) and below- (orange) normal precipitation during the next month. Darker shading expresses a higher probability. These figures are often misinterpreted because they appear to show where it will be wettest and where it will be driest, but that’s incorrect. Areas shaded in green may see below-average precipitation over the one-month period. So this figure should be used to place your bets as to which areas will receive above- or below-average precipitation. However, you’re given no information as to how far above- or below-average the precipitation is likely to be. Courtesy the NOAA Climate Prediction Center at www.cpc.ncep.noaa.gov

Though from my experience these outlooks tend to provide less useful information than we ever expect. In this case, there’s about a 60% chance that the SLC area will receive more precipitation than is normal for the next month—a 40% probability for equal-to- or below-average precipitation—according to climate models. These aren’t incredible odds if you ask me.


This Week

Looking at the more reliable short-term forecast, we see one big system heading toward the interior west as the week carries on.

500 mbar prog
12Z GFS 500 mbar absolute vorticity (shaded), valid 6 AM MT Monday 3/11 to 6 AM MT Thursday 3/14. This “500 mbar prog” is useful for making a quick analysis of the short- and mid-range forecast state of the atmosphere. Courtesy tropicaltidbits.com

Daytime temperatures at ski resorts begin relatively mild (around or just below freezing) through Tuesday night. Some instability today (Monday) and Tuesday may allow light snow showers or overcast to exist at high elevations.

The mild early-week air mass will give way to cold polar air in time for the next powder drop. A moderate snowstorm Tuesday night will usher in unseasonably cold air that will remain over a few days.

You can expect a period of heavy precipitation with the arrival of a cold front Tuesday morning, but altogether this is a quick-hitter. This storm should drop a nice layer of fresh powder overnight for the mid-week crowd, and then another thin coating throughout the daytime.


Snowfall Forecast

The snowfall forecast is still uncertain. Here’s mine, just to give you a sense of the range of possibilities for this event at Utah resorts.

probability forecast
Subjective probability forecast for snowfall during the mid-week storm. Note, most importantly, the range of possibilities for each forecast. These are based on a combination of model ensembles, primarily the GEFS.

So still some uncertainty heading into the next storm, and then quite a bit more uncertainty reserved for next week. My suggestion is that you brace for a cold powder day Wednesday, then hold your dice until late this week when the day 5+ forecast may become clearer.

-Marcel

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