915
FXUS65 KPIH 031011
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
411 AM MDT Fri May 3 2024

.SHORT TERM...TODAY THROUGH SATURDAY NIGHT...
It may be hard to believe given that it`s snowing early this AM
across portions of the forecast area, but we actually have some good
news in the short-term! First though...a trough is sitting over us
early this AM, supporting a mix of rain and snow for many areas. In
particular, a zone of light to moderate snowfall is situated across
the Arco and Mud Lake Desert region, Upper Snake Plain, and Teton
Valley, slowly trending south with time. Temps very near freezing
will make it difficult for the snow to effectively accumulate on
roadways, but motorists across this region should still be prepared
to encounter reduced visibility and localized slick or slushy
conditions at times, and an SPS has been issued through 7 AM to
highlight this risk. Accumulations should remain less than 1 inch on
the most impacted roadways, with a bit more possible on some grassy
and elevated surfaces. (This band of precip may be partially
convergence-induced, although sfc wind fields are a bit messy.) All
high-res models show general agreement in this band sinking south
across the Lower Snake Plain and adjacent terrain between 5 AM and
11 AM morning (as a mix of rain and snow with very little if any
accumulation south of Blackfoot in the Snake Plain), ending by noon
at which point the good news begins as breaks of sunshine develop
and high temps gain just a few degrees over yesterday`s readings!
Ran with the NBM today, except we massaged PoPs, Sky, and QPF this
AM to introduce very light snow accumulations along the path of this
precip band and slow down its progression timing just a bit. We will
continue to deal with frost/freeze potential for gardens and
sensitive crops up the ern Magic Valley/Snake Plain corridor through
Sat AM, but then high temps surge into the 60s and low 70s by Sat
afternoon. We continue to note a trend toward a later onset of
precip associated with the next approaching low pressure
system...likely not occurring until sunset in our far wrn zones, and
potentially as late as after midnight east of I-15. NBM guidance has
been a bit slow to reflect this trend but is catching up, and we
massaged PoPs lower in the forecast across the ern half of the CWA
Sat eve based on consensus across both high-res and coarser
deterministic models. (Also note Sat will be breezy regionwide.)
Thus, once we clear this morning`s rain/snow out, almost two full
days of drier (and eventually warmer) conditions are on tap! Enjoy
the break while it lasts, as unsettled wx returns for most, if not
all, of next week. 01

.LONG TERM...SUNDAY THROUGH NEXT FRIDAY...
East Idaho begins the extended period under the influence of deep
low centered over the northern Great Basin. Frontal passage early
in the day along with broad precipitation shield expected to
return region to very cool conditions with mountain snow and mix
of valley rain/snow into Monday. Thunderstorms will be possible
both days across portions of the region. Ensemble/NBM means total
generally 3-6" of snow accumulations Sunday and Monday for most of
the mountainous regions of East Idaho but high end 90th
percentile estimates are significantly higher at the 8-12" range.
Needless to say, Winter Weather Advisories will likely be needed
for higher terrain zones as the system approaches unless the
models take an unlikely drastic turn. Despite the cooler trend,
overnight lows remain above freezing initially, so minimal
accumulations are expected for the Snake Plain at this time. That
said, QPF amounts tell a different story. Ensemble/NBM means run
0.50-1.0", and peak values at the 90th percentile over higher
terrain reach around 2.0" of water. If the higher end percentiles
can be realized, East Idaho waterways could expect additional
rises in river/stream levels headed into the week.

Upper low shifts toward the northern Great Plains Tuesday into
Wednesday, transitioning into broad northwest flow over East Idaho.
Conditions remain cool and below normal. Windy conditions Monday
continue into Tuesday, with guidance supportive of Wind Advisories
throughout the Snake Plain. Unsettled conditions continue with
showers each day, and though temperatures remain cool, daytime
should be warm enough for valley rain. Ensemble clusters support a
return of a ridge along the coast by the end of the week. Cluster
means and NBM keep enough influence of lingering stretched trough
into the Great Basin, with only 10% of the ensemble membership
pushing ridge axis over East Idaho by Friday. DMH

&&

.AVIATION...
Small but well defined shortwave feature dropping southeast
through East Idaho early this morning producing a mix of wet
conditions across the region. MVFR DZ/-SHRA to the south will give
way to more consolidated band of IFR/LIFR -SN. Band is expected
to gradually shift south from KIDA/KDIJ to KPIH around sunrise,
then sag south through the southeast highlands and Bear Lake
through about 18Z. Behind the band of snow, expect slow clearing
back to MVFR. Generally VFR conditions are expected most areas by
early afternoon, though a few afternoon build ups will remain
possible. High VFR clouds are expected to spill across East Idaho
overnight, but conditions should remain VFR headed into the
beginning of the weekend. DMH

&&

.HYDROLOGY...
Moderate flooding remains ongoing at the Portneuf River at
Pocatello with the level dropping today or Saturday before rising
again early next week. Minor flooding continues for the Portneuf
River at Topaz where the gauge remains above flood stage and will
remain so for several days. Flood warnings also remain in effect
for the Blackfoot River near Shelley at Wolverine Canyon where the
river has gone above flood stage and also near Blackfoot where
the river has also now gone above flood stage. GK

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Frost Advisory until 9 AM MDT this morning for IDZ051-054-055.

Freeze Warning until 9 AM MDT this morning for IDZ052-053.

&&

$$