Area Forecast Discussion
Issued by NWS Pocatello, ID

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000
FXUS65 KPIH 121154
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
554 AM MDT Tue Mar 12 2024

...AVIATION UPDATED...

.SHORT TERM...TODAY AND WEDNESDAY...
As an upper trough moves onshore this morning, current satellite
imagery shows mid-level and high clouds filtering into Idaho
through the upper-level southwesterly flow. Associated
precipitation is already ongoing across SE Idaho as far east as
Pocatello north to Island Park. With widespread overnight
temperatures still in the upper 30s across the lower elevations,
snow levels are generally above 5,000 feet areawide. There is a
short window through around 10 AM this morning during which light
snow accumulations of around a Trace to half inch will be possible
along the I-15 corridor from Pocatello north. A cold front will
shift eastward through the region this afternoon, with hi-res
models continuing to show convective enhancement associated with
the frontal passage. This would result in higher snowfall totals
under these enhanced snow bands with chances for lightning, gusty
winds, and quick reductions in visibility where temperatures
support snow. The HREF continues to feature a 10-30% probability
of thunder generally south of the Snake Plain, extending from the
Shoshone area further south and east. Furthermore, the Storm
Prediction Center now includes all of Idaho in a general risk of
thunder today. Snow levels will drop below valley floors overnight
tonight behind the front which will allow for minor accumulations
throughout the day Wednesday in our valleys. Of greater impact
could be a potential Snake Plain convergence setup, with strong
signatures on hi-res models for surface winds to converge
Wednesday afternoon as a closed low develops over Idaho and drops
south into Nevada/Utah. While exact amounts and timing will be
tricky to pin down, 2 to 3 inches could accumulate along the
western benches of Pocatello with around 1 to 2 inches in Idaho
Falls and further north. Be sure to stay informed of the latest
updates and conditions if you plan to travel during this
timeframe. For our higher elevations, accumulations of 4 to 10
inches with localized higher totals above pass levels remain on
track for the Sawtooths, South Hills, Big Holes, Centennials, and
Bear River Range, where WINTER WEATHER ADVISORIES remain in place
through Wednesday afternoon. Cropp

.LONG TERM...THURSDAY THROUGH NEXT TUESDAY...
A ridge of high pressure centered along the Pacific coast will
gradually exert increasing influence inland across the nrn Rockies,
leading to growing confidence in a long-duration period of dry,
mostly clear/sunny, low-impact wx from Thu right into early next
week. The ridge will tend to flatten at some point next week with a
fresh storm eventually cutting into it from the north. Right now,
next Wed is favored for this across the deterministic model suite.
500mb height cluster analysis offers high confidence in the ridge
dominating through Mon, with about 40% of the ensemble space at
least mildly hinting at some potential for troughing cutting in
somewhere across the PacNW as early as Tue (although with little to
no precip reaching our CWA). High temps are likely to gradually warm
throughout the period, with low 50s becoming widespread at lower
elevations by Sun, and potentially some 60s working into the ern
Magic Valley and Raft River area by next Tue. The longer we hold
onto the ridge, the warmer temps will climb! 01

&&

.AVIATION...
The main event has arrived. Precip is expected to come in two rounds
today...the first more widespread/stratiform through 15-16z/9-10am
this AM depending on the terminal (except lingering until 19z/1pm or
so at KDIJ). Cigs are quickly crashing to MVFR with this round, and
even IFR at KSUN, so have blended NBM guidance with current obs for
our forecast with this first round. Cigs will likely control the
impact, as while snow may mix in or dominate at KSUN and KIDA, vsbys
have not dropped quite as low as forecast so far and temps are quite
marginal with precip switching back and forth between rain and snow.
KDIJ may be cold enough that 2SM could dominate as soon as precip
becomes more established there. We then generally advertise a brief
period of opportunity for cigs to lift just SLIGHTLY and perhaps
develop some breaks in the deck late this AM/midday, before round
two arrives...characterized by more showery precip and even a few t-
storms near KBYI and KPIH (so have added VCTS at these terminals).
We generally nudge back toward VFR cigs this afternoon except KDIJ,
but overall confidence in these cigs is low...NBM and MOS guidance
doesn`t reflect much improvement, but given a transition toward a
more showery/convective environment with some breaks, a slight
improvement seems probable. Gusts to 20kts are possible at KIDA
today. Expect a regional lull tonight, but just beyond the end of
the 12z TAF period we expect wind-convergence-induced snowfall to
redevelop in the Snake Plain potentially impacting KIDA and KPIH, so
another round of MVFR to IFR cigs/vsbys is possible with that
activity starting Wed AM depending on it`s exactly track/evolution.
Stay tuned. Strong westerly winds will also develop by 08z at KBYI
and increase further beyond the end of the TAF period, lasting
throughout Wed. 01

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 10 PM MDT this evening for IDZ056-
072.

Winter Weather Advisory until 4 AM MDT Wednesday for IDZ060-064.

Winter Weather Advisory until 3 PM MDT Wednesday for IDZ066.

&&

$$


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