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FOUS11 KWBC 181811
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
211 PM EDT Fri Apr 18 2025

Valid 00Z Sat Apr 19 2025 - 00Z Tue Apr 22 2025


...Central/Southern Rockies & Adjacent High Plains...
Days 1-2...

Significant mid-April winter storm continues through Saturday
evening, bringing heavy snow primarily to the higher terrain of CO
and NM before ending from west to east.

As of this morning, the amplified but positively tilted trough is
clearly evident on GOES-E WV and IR imagery, centered across Utah.
This trough will continue to amplify, and as the northern portion
of this trough ejects to the east, the southern portion will close
off across the Four Corners. This amplification will result in
pronounced downstream synoptic lift, as mid-level divergence
intensifies and at least peripherally overlaps with the LFQ of a
poleward arcing jet streak into the Central Plains. At the same
time, the cold front being driven south by the amplified trough
will dig into Texas and reach the Rio Grande Valley by the end of
D1, leaving impressive 850-600mb fgen in its wake tilted north into
NM and CO. This even more enhanced ascent will overlap with upslope
flow on post-frontal E/NE winds, to drive intense snow rates across
the Front Range, Sangre de Cristos, and San Juans through D1 and
into early D2 (lingering farther south into D2).

This deep layer ascent (and additional mesoscale through
fgen/upslope) will occur within a moistening column as 700-300mb
flow remains out of the SW downstream of the primary trough axis.
Although PWs progged by NAEFS will be around normal values, this
will be sufficient to be wrung out as heavy snow, with rates
possibly (50-60% chance) exceeding 1"/hr, especially in the Sangres
and San Juans. Snow levels will be falling during this time as
well, reaching as low as 3000 ft, producing significant impacts
even at pass levels across much of the region.

The more challenging aspect of this forecast remains what will
happen in the I-25 urban corridor and eastward into the High
Plains/lower elevations. While it is likely that heavy snow will
accumulate across both the Palmer Divide and Raton Mesa, the NBM
probabilities have dropped off a bit into the lower elevations
including the urban corridor. With impressive ascent likely even
into the High Plains, it still seems plausible that at least
periods of heavy snow will impact the lower elevations, and WSSI
features at least minor impacts, but still a plowable snow is
probable across much of the CO foothills and into northeast NM.

For the remainder of this event, the heaviest snow is likely across
the Sangre de Cristos and the San Juans, where WPC probabilities D1
are high (>70%) for more than 12 inches of snow, and locally 18-24"
is possible through D2 despite rapidly waning coverage and
intensity of snow after 06Z Sunday. Some moderate snowfall of 4-6
inches is also expected across portions of the Mogollon Rim, White
Mountains of AZ, and other higher elevations of northern AZ through
D1.



The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Weiss






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