Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
331 AM EDT Tue Apr 25 2023

Valid 12Z Tue Apr 25 2023 - 12Z Fri Apr 28 2023

...Colorado Rockies...
Days 1-2...

A robust late season winter storm will impact the central Rockies
today into early Wednesday with significant accumulations for the
higher terrain into the Front Range. Mid-level closed low and
surface cold front over Utah this morning will continue
southeastward into and through Colorado today with snow expanding
out of Wyoming (especially the Wind River Range) and through the
Rockies. Deep moisture flowing northward out of the western Gulf
of Mexico will turn to the west into the Front Range/Rockies this
afternoon bringing precipitable water values to near 0.50" along
the I-25 corridor. By this evening, as the upper low skips across
southwestern CO, 700mb flow will increase out of the east across
the High Plains with increasing snow rates of 1-3"/hr likely in
heavier bands due to strong surface convergence and upslope
enhancement. Saturated column and strong upward vertical
velocities may help to bring the snow level a bit lower through
the Foothills as surface temperatures cool to the low 30s past
sunset. By Wednesday morning, the upper low is forecast to be over
northeaster NM with snow starting to wind down from north to
south.

Heaviest axis of snowfall will be along and east of the Divide
owing to easterly upslope enhancement, where 1-2ft will be likely
above 8000ft. However, even over the San Juans, nearly under the
path of the upper low, amounts over six inches are likely. Thermal
profile east of the Foothills becomes less clear with temperatures
in the low to mid 30s with rain over the Plains and rain ending as
some snow in between. Higher elevations like the Palmer Divide
will also see appreciable snow but this will increase over the
Raton Mesa and especially the Sangre de Cristos as well, which
will see snow continue into the early part of D2. WPC snowfall
probabilities of at least 12 inches of snow D1-2 are high (>70%)
above 8000-9000ft and are moderate (>40%) for at least 4 inches of
snow above 6500ft or so.


...Northern/Central Rockies to Western High Plains...
Day 3...

A mid-level shortwave is forecast to dive southeastward out of
Canada early Thursday then southward through WY/CO in response to
building upper ridging over the Pacific Northwest. This will drive
a cold front southward with a drop in temperatures behind it and
rain changing to snow for many areas in its wake. Northerly to
northeasterly flow post-FROPA will favor the Bighorns and Black
Hills were several inches of snow are possible. Front will be a
fast-mover and spread snow southward all the way into the CO
Rockies by Friday morning as snow levels fall to near 5000ft. WPC
probabilities for at least 4 inches are generally below 50% in
most areas except for the Bighorns (50-70%).


The probability of significant icing greater than 0.25" is less
than 10 percent.


Fracasso