FOUS11 KWBC 041907
QPFHSD
Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
307 PM EDT Mon May 4 2026
Valid 00Z Tue May 05 2026 - 00Z Fri May 08 2026
...Wyoming and Colorado...
Days 1-3...
A late season winter storm will produce periods of heavy snow
through mid-week to not only the Central Rockies, but snow levels
will be low enough to deliver accumulating snowfall to the I-25
corridor Tuesday. The meteorological setup consists of a shortwave
trough associated with the polar jet stream over the Northern
Plains diving southward towards a positively tilted closed-low
associated with a robust subtropical jet stream in the Southwest.
200mb winds over southeast NM and much of NM are above the 97.5
climatological percentile per NAEFS, which is playing a big role in
the development of an IVT over southern NM and west TX that is
among the strongest for this time of year in the CFSR database. The
250mb jet streak associated with the polar jet will place its
divergent left-exit region over the southern WY and much of CO at
the same time Canadian high pressure building in from the north
causes enhanced upsloping easterly flow.
With no shortage of 850-300mb moisture, periods of snow will begin
to unfold tonight over the Front and Park Ranges of CO, as well as
the Medicine Bow and Laramie Ranges of WY. As the best upper-level
divergence moves in aloft on Tuesday and low-level winds
strengthen, precipitation rates will increase and snow levels will
crash to the valley floors in WY with snow beginning to accumulate
along the I-25/I-80 corridor in southern WY. By Tuesday afternoon
and evening, any rain will transition to snow from I-25 east of the
Flat Irons on south to the Palmer Divide. Snow will accumulate
more efficiently after sunset, which coincidentally will be when
the Denver/Boulder metro area is likely to witness its heaviest
burst of snow from this event. Snow is also expected to accumulate
along the I-70 corridor east of Denver and perhaps as far east as
far northeast KS. The WPC Snowband Probability Tracker shows
instances of 1-2"/hr snowfall rates over northern CO and far
southern WY, with some >3"/hr rates possible in the Front Range.
Snow will work its way south early Wednesday morning through the
Sangre De Cristo and San Juans as snowfall rates gradually diminish
from the Cheyenne/Fort Collins area. By Wednesday afternoon and
evening, only the Sangre De Cristo, San Juans, and Raton Mesa are
likely to see accumulating snowfall. Snow is likely to conclude in
the higher elevations of northern NM before sunrise on Thursday.
WPC probabilities highlight the stark contrast in these classic
late-season snow events, as well as the impacts of urban heat
islands. 24-hour probabilities for >6" of snow are generally
between 20-40% in the Denver metro, whereas at elevations >6,000ft
are over 50% for snowfall totals >6". Unsurprisingly, the mountain
ranges will be the big "winners" for this event. The CO Front
Range, including Rocky Mountain NP, sport high chances (>70%) for
snowfall amounts >18" for this event. In fact, Moderate-to-high
chances (50-80%) for snowfall totals >12" are present in the
Medicine Bow and Laramie Range of WY, as well as the Park Range and
the peaks of the Sangre De Cristo.
This winter storm will produce much needed snowfall in the drought-
stricken Central Rockies and High Plains. However, unlike last
week's event which had less snowfall and was confined to the higher
elevations, this event is more significant and will impacts both
commerce and infrastructure. The WSSI highlights widespread Minor
Impacts (winter driving conditions; use caution while driving) from
southeast WY to as far east as the CO/KS border along I-70 and as
far south as the Sangre De Cristo. Moderate Impacts are denoted
from the Laramie Range and Medicine Bow on south along the Front
Range, with some Major Impacts (considerable disruptions;
widespread closures and potential infrastructure impacts such as
power outages and tree damage) are present in the higher elevations
of these ranges, including Rocky Mountains NP. The heavy/wet nature
of the snowfall on trees fully in bloom and on power lines could
result in tree damage and power outages.
The probability for significant icing over one-tenth of an inch is
less than 10 percent across the CONUS.
Mullinax
$$
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