Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
329 AM EDT Tue Oct 14 2025
Valid 12Z Tue Oct 14 2025 - 12Z Fri Oct 17 2025
...California & Central Great Basin...
Days 1-2...
...First significant snowfall event of the season continues across
the Sierra Nevada today...
A deep, vertically stacked mid-upper low churning off the coast of
central CA by the start of the forecast period (12Z Tues) is
forecast to swing inland today before crossing into the central
Great Basin on Wednesday. This mid-upper low pressure system is
very anomalous for the time of year, reaching below the 0.5th
climatological percentiles and nearing October records for the
first part of day 1 just of the CA coast. The depth of the system
will allow for ample upper ascent and orographic lift throughout
the Sierra Nevada, while decreasing snow levels from around 7000ft
this morning to as low as 5500ft this evening under the upper low.
Snow levels also drop to around 6000ft over the central NV ranges
by Wednesday. The strong inland moisture surge ahead of the low and
associated with an occluded/cold front will have IVT values around
500 kg/m/s at the start of the forecast period and allow for
moderate to heavy snow rates above the snow level. 00Z HREF mean
snow rates are 1-2"/hr over the central/southern Sierra Nevada from
12Z to 18Z today, with lingering bursts of 1"/hr snow possible
over the central Sierra underneath the upper low through Tuesday
night.
WPC probabilities show moderate-to-high chances (40-80%) for at
least 12" of additional snowfall after 12Z Tuesday above about
8000ft and greatest across the southern Sierra and White/Inyo Mts
just to the east. Probabilities through that time for >8" are also
40-80% around 7000ft (including Donner Pass on I-80). The WSSI
highlights Major Impacts for the High Sierra and remote central NV
ranges with moderate impacts for most cross Sierra road passes.
...North-Central Rockies...
Days 2-3...
The low fills as it crosses the Great Basin, but remains closed as
it crosses over WY on Thursday. Lee-side cyclogenesis forms over
southeast WY Wednesday night with an increasing easterly component
to the low level flow to aid moisture transport over the western WY
ranges through Thursday morning with snow levels falling to around
7000ft after starting above 9000ft on Wednesday. Overall, snowfall
rates
are not expected to be that great outside of an isolated convective
shower in the highest terrain with mainly longer duration
light-to-moderate
snow through the forecast period. WPC probs for >8" snow in 72hr
ending 12Z Friday are 60-90% for the Absarokas, Teton and Wind
River Range, as well as the Uinta Mts in Utah mainly above
10,000ft.
The probability of significant freezing rain across CONUS is less
than 10 percent.
Snell