FOUS11 KWBC 040704
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
204 AM EST Mon Nov 4 2024

Valid 12Z Mon Nov 04 2024 - 12Z Thu Nov 07 2024

...CO/NM border...
Day 1...

Upper low over NM this morning will lift northeastward across the
TX Panhandle this evening. Snow on the NW side of the low within a
region of modest PVA and enhanced upslope into the Raton Mesa will
continue for the first part of D1 before tapering off later this
evening and overnight. Lighter snow will extend eastward into the
far western OK Panhandle as rain changes to snow. WPC probabilities
for at least 8 inches of snow are >50% above 9000-10,000ft over
portions of central/northern NM and across the CO line.


...Northwest and Northern/Central Rockies...
Days 1-2...

Next system coming into the PacNW will be the last for at least a
little bit in what has been quite a busy stretch. Warm front will
move ashore today bringing in a surge of moisture and rising snow
levels up to around 4000ft to the north and 6000ft to the south
over the WA Cascades, but only rising to around 5000ft farther east
toward the Divide. Strong and favorable upslope flow will maximize
over the WA Cascades where a few feet of snow will be possible at
the higher peaks. By late in the evening and overnight into
Tuesday, snow levels will fall to around 3000ft bringing
accumulating snow to many of the lower passes across the Cascades.
WPC probabilities for at least 8 inches of snow are >50% above
3500ft or so. Upper jet will continue inland and promote moderate
snow across the northern ID ranges into northwestern Montana. Into
D2, the mid-level vort will deepen and split, with the northern
portion closing off along the MT/Canadian border before pivoting
back southward Tuesday evening over central MT. This will maintain
modest snow over the central MT terrain (i.e., Little Belt and Big
Snowy Mountains) on upslope northerly flow. There, WPC
probabilities for at least 8 inches of snow D2 are >50% above
4000ft or so. The southern portion of the mid-level trough will dig
into the Great Basin through early Wednesday, spreading snow
across UT/CO where several inches are likely, especially into the
CO Rockies. By the end of D2, an upper low will start to close off
over the Four Corners region, setting up the next phase of the
system.


...Four Corners...
Day 3...

Aforementioned upper low is forecast to be situated over eastern
UT early Wednesday morning and will likely sink southward through
the day to a position over eastern AZ by the end of D3. This will
keep a relatively consistent SW to S flow over northern NM into
southern CO, which is quite favorable for upslope enhancement over
the San Juans and into the Sangre de Cristos among other ranges.
Multiple waves of PVA will rotate around the upper low and across
the region, favoring moderate to heavy snow at times with a high
likelihood (>60% chance) of moderate impacts per the
probabilistic WSSI. WPC probabilities for at least 8 inches of
snow are >50% above 6000-8000ft and probabilities for at least 4
inches >50% down to around 5000-7000ft. Colder air filtering into
northeastern CO will also promote light to perhaps modest snow over
the I-25 corridor with heavier totals likely into the Palmer
Divide. Heavy snow is forecast to continue past the end of D3 as
the system slowly moves through the region. Please see the Winter
Weather Outlook and the Probabilistic Winter Storm Severity Index
(WSSI-P) for more information.

The probability of significant ice across the CONUS is less than
10 percent.

Fracasso


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