826
FXUS65 KPIH 170857
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
257 AM MDT Mon Jun 17 2024

.SHORT TERM...Today through Tuesday night. Satellite imagery shows
shortwave feature working through Oregon early this morning. Radar
imagery indicated showers have begun to creep towards the western
edges of the forecast area, with some light returns and perhaps a
sprinkle or two across the Island Park area where southwest flow
appears to be aiding orographic lift. Upper low is projected to
swing into the Idaho panhandle through the day, swinging cold
front through the region, along with associated showers/storms
and of course, wind. Most of the convection should be confined to
the central mountains/Island Park/northern half of the eastern
highlands today, but the HREF including the NAM nest and the HRRR
appear to drag a band of convection across the Upper Snake area
this evening as well. Given the cooler temperatures, the storms
are not expected to be particularly strong. Winds are the next
impact of concern today, and a Wind Advisory is in place for a
significant portion of the Snake Plain. Have extended the Wind
Advisory across the northern portions of the Eastern Magic Valley,
namely the Shoshone zone. If stronger winds can materialize
toward the higher end of the probabilities (90th percentile - 1 in
10 chance of exceedance), the Arco Desert/INL region could reach
into the lower end of High Wind Warning, but right now there is
little confidence in this scenario materializing, given the cloud
cover and expected precipitation during peak wind hours. Winds
drop off rapidly this evening. Unseasonably cool temperatures
today lead to very cold temperatures tonight. A Frost Advisory is
in place for tonight for the entirety of the Snake Plain, with
temperatures dropping to or below 36 degrees. Caveat - the urban
centers through the I-15 and I-86/I-84 corridors may remain just
above those temperatures. Nevertheless, covering gardens and
bringing sensitive plants indoors where possible might be prudent.
Another round of showers is expected during the day Tuesday,
mainly north. Temperatures remain very cool, with lower elevation
daytime highs in the 60s. Another round of cold temperatures is
expected Tuesday night, though slightly warmer than tonight.
Another Frost Advisory is likely, mainly for the upper portions of
the Snake Plain. DMH

.LONG TERM...Wednesday through next Monday. We will see a
significant transition from the unseasonably cool and unsettled
conditions on tap for early this week to much warmer and drier
conditions by late week into the weekend. EPS and GEFS ensemble
means are in good agreement showing the upper low responsible for
the active weather in the short term filling and shifting well
northeast of the area by early Wednesday, leaving the region in a
weak southwest flow aloft between a remnant weak trough axis along
the West Coast and expansive ridging over the Eastern CONUS. The
main impacts of this forecast period may come at the onset with
another unseasonably cool morning on tap Wednesday morning, although
not as cold as the previous night. Still it appears that
temperatures may again dip into the mid 30s in parts of the Snake
Plain primarily north and east of Pocatello, potentially yielding
one more round of frost concerns. Current NBM probabilities show a
40-60% chance of temperatures falling below 36F Wednesday morning in
these areas. Beyond Wednesday morning, a notable warming trend will
commence under progressively rising heights amid a continued weak
southwest flow aloft. High temps will climb 8-10 degrees Wednesday
and another 8-10 degrees Thursday, putting values some 5-8 degrees
above normals by Thursday, quite the swing from the 20 degree below
normal values expected today. This warming trend will continue into
the weekend as shortwave ridging amplifies ahead of a system
approaching the BC coast, likely pushing lower valley highs into the
lower 90s and higher elevations into the 70s and 80s. Current NBM
probabilities suggest a roughly 50-70% chance of highs in the
Interstate corridor from Burley to Pocatello to Idaho Falls
eclipsing the 90F mark by Sunday. WPC cluster analysis shows fairly
strong agreement for this pattern, although by early the following
week toward the end of this forecast period we start to see some
differences emerge with the strength of the upper low skirting east
along the Canadian border. About 40% of the cluster membership shows
a stronger system, which would support cooler temps toward the end
of the period, while the other 60% advertise a weaker system and
resultant warmer temps. A stronger system passing to our north would
also lead to stronger winds Sunday/Monday. Precipitation chances
appear minimal through the long term period, although a few light
showers cannot be ruled out with weak shortwave impulses riding
through the flow. Friday across the Eastern Highlands currently
looks most favorable for any such light shower activity. Overall, a
pronounced warming trend and primarily dry conditions will be the
theme from mid-week into the weekend. KB


&&

.AVIATION...An unseasonably strong low pressure system and attendant
cold front will push across the region today, bringing strong winds
and shower/thunderstorm chances to the terminals. Although a few
light showers may impact any of the terminals, KDIJ will be favored
for more prevailing shower activity both along the front and with
wraparound showers around the low. Primarily VFR conditions are
anticipated, with reductions to MVFR possible in heavier showers.
West/southwest winds ramp up this morning, with KPIH and KIDA seeing
the strongest winds, where gusts will increase to around 35 kts this
afternoon. Winds will dissipate late this evening, becoming light
after 06Z Tuesday. KB


&&

.FIRE WEATHER...An upper-level low pressure system and attendant cold
front will push across the region today, ushering in an unseasonably
cold airmass. High temperatures today will run roughly 20 degrees
below seasonal normals for mid June, struggling to reach 60F in many
of the lower valleys except along the UT border. Today will be the
coldest day of the next week, with a steady warming trend beginning
Tuesday as the low pressure system weakens and shifts northeast of
the area. Cold overnight lows can be expected the next couple of
nights, falling into the 30s even at low elevations. Westerly winds
will crank up today with the cold frontal passage, and will be
strongest in the Snake Plain and Eastern Magic Valley, where gusts
of 40-50 mph are expected (40-70% chance of gusts exceeding 45 mph).
Precipitation chances will also accompany the storm system today and
tonight, including high-elevation snow above 6500 ft. Ridgelines in
the Central Mountains above 8 kft could see several inches of heavy
wet snow. For lower elevations, showers and embedded thunderstorms
will accompany the upper low and cold front today into tonight.
Higher precipitation amounts favor northern portions of the forecast
area from the Central Mountains east along the Montana Divide.
Chances for greater than 0.1" of liquid precipitation exceed 70%
from the Sawtooths east into the Island Park area, but drop off
sharply to less than 20% south of a Hailey to Blackfoot to Afton, WY
line. Some light precipitation will linger into Tuesday primarily
from the Central Mountains east along the Divide into the Eastern
Highlands on the backside of the upper low. Dry conditions then
return for Wednesday, along with warming temperatures climbing above
average by late week. Temperatures continue to climb into next
weekend, reaching the low 90s in lower valleys. We may see
increasing winds again by late next weekend as a low pressure system
passes to the north. KB


&&

.HYDROLOGY...
The flood warning has been dropped for the Snake River as Heise as
flooding is no longer expected as river levels continue to drop.
Warning remains hoisted for the Teton River at Driggs. Water
levels remain very close to flood stage, but are still forecast to
drop. The warning can likely be dropped today if the forecast
comes to fruition. McKaughan/DMH

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Frost Advisory from 2 AM to 9 AM MDT Tuesday for IDZ051>055.

Wind Advisory from noon today to 8 PM MDT this evening for
IDZ051>054.

&&

$$