Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
435 PM EDT Tue Apr 27 2021

Valid 00Z Wed Apr 28 2021 - 00Z Sat May 01 2021

...Four Corners...
Day 1...

A closed 700 mb low will move slowly east across the southwest
through Wednesday. A front from 700-300 mb drifts east across
Colorado, with the overlap of low level relative humidity above 90
percent and 700 mb ascent over northeast CO into the foothills and
front range.  A jet streak will intensify downstream of the
primary trough axis, placing favorable diffluence over CO/NM, with
divergence aloft, creating the strongest ascent over CO with
secondary maxima over NM.

Locally heavy snow is expected over the front range where a
combination of moisture, synoptic lift, orographic lift, and mid
level frontal ascent persist tonight.
This suggests the heaviest snow will be confined to the Front
Range where a prolonged period of intense ascent will bring heavy
snow through tonight, with snowfall rates potentially eclipsing
1"/hr as shown by the HREF. WPC probabilities for 8 inches are
high in the Front Range, with more than 12 inches likely in some
locations above 8000 ft.
As the 700 mb front moves south through southern CO into NM, snow
in CO winds down on Wednesday.

Several inches of snow are likely in the mountains of southwest
New Mexico and adjacent southeast Arizona as the upper low
approaches and the mid level front crosses the region, producing
locally heavy convergence and ascent near the front. Given the
short window of enhanced ascent, probabilities for 8 inches of
snow are low.
The event winds down Wed evening as the 700 mb low and front move
south out of the region and drying aloft develops.

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

Petersen