Winter Weather in Idaho, February 2 to 3, 2021

Area Forecast Discussion
National Weather Service Pocatello ID
532 PM MST Tue Feb 2 2021

.SHORT TERM...Tonight through Thursday night...Upper trough has been
slow to move inland. Precipitation has started to move into the
Central Mountains per area web cams.  Frontal boundary still west of
the state but precipitation starting to fill in ahead of the front
per radar imagery. Aside from the slightly lower start, trough and
precipitation progression appears to remain on track. Snow continues
to target higher elevations primarily Central Mountains and Eastern
Highlands. Warm southerly flow has induced very warm temperatures in
lower elevations, especially along and south of I-86. Precip shifts
into the Snake Plain and eastern highlands around/after midnight,
and temperatures may be warm enough to the south for precipitation
to at least start as rain. NAM soundings support burst of moderate
snow along the front as it passes through Pocatello. Given the
strong warming this afternoon, may be more difficult to lower
temperatures enough to accumulate any meaningful snow in the
Pocatello region before sunrise, but character should shift to all
snow with frontal passage. Surface winds increase behind the front
and will be quite breezy, but blowing snow may be minimized if the
temperatures can stay warm enough. Upper trough shifts through
during the afternoon.  This may not be well picked up with the short
term ensembles yet, and will be feature to watch over the next
forecast cycle or two. Otherwise will likely see additional light
snow showers continue over higher elevations into late Wednesday.
Cool northwest flow is in place for Wednesday night into late
Thursday. Reinforcing shortwave arrives from the northwest Thursday
night, producing upslope snows in portions of the central mountains
and most of the eastern and southern highlands into Friday. DMH

.LONG TERM...Friday through next Tuesday.
The long term portion of the forecast will be characterized by
persistent northwest flow, at least through Monday or so, as central
and eastern Idaho will remain in between a ridge of high pressure
across the eastern Pacific and a strengthening polar vortex near the
Great Lakes and northern Great Plains. A disturbance embedded in the
flow will pass through the region on Friday. Snow showers will be
ongoing by daybreak Friday morning across the eastern highlands/WY
border region and also across the central Idaho mountains. The
western edge of the snow shower activity is a bit uncertain and will
straddle the I-15 corridor, so it is possible that snow showers
activity could extend west to the Pocatello to Idaho Falls corridor
during the day Friday.  Snow shower activity should peak in coverage
and intensity midday, then gradually wind down through Friday night.
A second, weaker disturbance will briefly re-invigorate snow shower
activity over the same locations late Friday through Saturday. A few
inches of snow are expected across the eastern highlands during this
period. From Saturday night through much of Monday, lingering
moisture within the NW flow pattern will promote a continuation of
occasional light snow showers over the same areas. WPC clusters
generally indicate decent condifence in this pattern, with lesser
likelihood for the ridge to take hold over the western U.S., as some
earlier solutions were suggesting. One interesting trend to watch is
there is a slight nod toward a trend indicating the southwest
portion of the cold air associated with the above-mentioned polar
vortex could reach farther west into Montana and Wyoming. This
scenario could bring arctic air as far west as the Continental
Divide, along with the potential for much colder temperatures than
currently forecast across portions of east Idaho (particularly near
the Montana border) from Sunday into early next week. This is
something that will bear watching, but at this point the going
forecast reflects the most likely scenario as it stands currently.
The forecast becomes less certain at the end of the forecast period
as it appears the upper pattern will begin to break down and evolve.

AD

&&

.AVIATION...
A short wave trough and associated cold front will move across
central and eastern Idaho tonight. Ahead of the front, breezy
southerly winds in the 15-25 kt range will be ongoing from KBYI to
KPIH into this evening. Snow showers associated with the approaching
system will develop first for KSUN around 00Z this evening, and be
heaviest through 03-10z, with IFR conditions.  Brief reductions to
MVFR are possible. A RA/SN mix will develop at KBYI around 08z then
transition to snow around 10z followed by KDIJ shortly thereafter.
Similar reductions to IFR or perhaps briefly to MVFR as the band of
snow moves through. Have added TEMPO groups to account for this, as
the duration should be 1-3 hours,. Lingering low stratus and -SHSN
should linger through the balance of the morning at all TAF sites
before conditions improve by late morning. Although predominant VFR
conditions are expected during the afternoon, occasional snow
showers could result in temporary reductions. Breezy SW/W will
develop immediately behind the frontal boundary, with 15-25 kt winds
with occasional gusts through the morning hours, with the likely
exception of KSUN.  Wind shear will likely accompany the frontal
boundary passage as well. By late tomorrow afternoon/early evening,
snow shower chances and winds will decrease.

AD

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
None.

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