Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
419 PM EDT Mon Apr 26 2021

Valid 00Z Tue Apr 27 2021 - 00Z Fri Apr 30 2021

...Intermountain West to the Rockies...
Days 1-2..

A closed 500mb low over northern NV will stall there through
Tuesday as a reinforcing shortwave trough currently off the CA/OR
border closes into a low center as it reaches the northern Baja
peninsula late Tuesday and becomes the dominant low center with
this system/trough as it drifts east over the southern tier of the
CONUS through the next several days. The downstream southwesterly
trough reaches its peak intensity (a little over 130kt) over NM
Tuesday night and with persistent mid-level confluence/warm and
moist advection will produce high mid-level RH and PW anomalies
reaching more than +1 standard deviation above the climo mean.
This moisture will continue to be wrung out as it drifts east as
periods of rain and mountain snows (snow level generally 6000 to
7000ft) over northern AZ, southern and eastern UT and into western
CO and up across WY tonight. Lee-size low pressure developing over
eastern CO tonight will put a precip focus on north-central CO for
Tuesday afternoon through Tuesday night before drifting south to
northern NM through Wednesday evening.

Day 1 snow probabilities are moderate to high for 6 or more inches
for the highest peaks of AZ (along with the Kaibab Plateau), the
southern UT ranges, the Uintas of northeast UT, and the Wind
River, southern Absarokas, and Big Horn of WY along with the
western San Juans of CO. Day 1.5 snow probs center on the Front
Range of CO with moderately high probabilities for a foot or more
along the entirety of the CO Front Range. Then on Day 2 moderate
probabilities for 4 or more inches expand south down the Sangre de
Christos into NM.


...Northern Great Lakes...
Day 1...

Surface temperatures will remain around in the Arrowhead of MN and
interior sections of the western UP while southerly 850mb flow
will maintain a warm nose and enough moisture to keep a threat for
continued light freezing rain in pockets of these areas of MN/MI
through this evening where a few hundredths additional ice
accretion is possible after 00Z.


For Days 1-3, the probability of significant icing (0.25 inch or
more) is less than 10 percent.

Jackson