Red Flag Warning 1, NWS Pocatello, ID

Area Forecast Discussion
National Weather Service Pocatello ID
228 PM MDT Mon Jul 24 2023

.SHORT TERM...Tonight through Tuesday night.
Main impact this evening will be thunderstorms and associated
winds and possible rain from that across entire region. We are in
marginal threat for severe storms as well but extensive cloud
cover may mitigate the extent of severe thunderstorms a bit. On
Tuesday flow aloft shifts from south southwest to west southwest
which will limit monsoonal push of moisture a bit and expect much
drier conditions but also a significant wind increase especially
in the Arco and Mud Lake Desert and Lost River Range where winds
will be highest tomorrow. This will effect fire weather as well. A
wind advisory has been issued for the Arco and Mud Lake Desert as
well where sustained winds may push 30 mph with gusts near 50 mph
are expected. Winds won't be as strong elsewhere but gusts of 20
to 30 mph will be widespread. No thunderstorms are expected
Tuesday as the westerly flow aloft should suppress activity to the
south. It will remain slightly cooler Tuesday with highs mainly in
the 80s to lower 90s in lower elevations.
GK

..LONG TERM...WEDNESDAY THROUGH NEXT MONDAY...
A bit of a broken record continues in the long-term portion of the
forecast, if you've been following our discussions over the past
several days. A broad ridge of high pressure is forecast to remain
anchored over the Four Corners region right through next weekend
(perhaps slowly drifting east with time), with occasional hints of
SW monsoon moisture creeping far enough north under the high to
support a few isolated t-storms especially Wed and Thu, and
especially across the srn/ern highlands. At-large, however, most of
the CWA will remain dry, and overall WPC-modeled QPF holds at only a
few hundredths of an inch at best. Meanwhile, breezy conditions are
expected across the region throughout the period as two low pressure
systems track eastward across srn Canada, tightening the pressure
gradient against (and flattening) the ridge. The first will keep
enhanced winds going Wed afternoon (similar to Tue) with SW gusts
ranging from 20 MPH across the south to up to 50 MPH across the
Central Mntns, especially in the higher terrain and downslope-
favored locales. There is up to a 70% chance of exceeding 40 MPH
gusts across the Arco Desert and Shoshone lava beds, as well as
along the Montana border. Gusts over 40 MPH are likely across the
Central Mntns, with a 50-60% chance of exceeding 50 MPH. The ridge
tries to briefly reamplify Thu, before the second low passes to our
north sometime in the Fri/Sat/Sun window keeping winds going and
perhaps enhancing them again, but failing to provide meaningful
precip to break the overall sunny/hot/dry pattern. Temps throughout
the period will remain slightly above average for late July,
reaching into the 90s at lower elevations. All things considered,
aside from an isolated strong t-storm, the main wx impacts
throughout the next 7 days will be on the fire wx front as fuels
continue to dry out under this pattern. Our first RED FLAG WARNING
of the season has been issued for portions of the region for Tue,
for a combination of those gusty winds and critically low RHs. 01

&&

.AVIATION...
Main impact tonight will be thunderstorms this evening with
potential at all TAF sites through 03 or 04Z. Tuesday will be much
drier but with increased winds as drier air pushes into eastern
Idaho. Wind gusts will likely be in the 20 to 30 knot range at all
sites Tuesday after 18Z. Breezy conditions will continue through
much of the week. GK

&&

.FIRE WEATHER...
The overall forecast remains unchanged. On the synoptic scale, a
broad ridge of high pressure will remain anchored over the Four
Corners region (trending a bit east with time), while a series of
two low pressure systems tracking east across srn Canada this week
try to flatten/break down the influence of the ridge locally and
increase winds. The result: a warm, dry, breezy pattern is expected
to remain in place throughout the next 7 days, continuing the drying
trend in our fuels. The first low will maximize SW winds tomorrow
and Wed afternoons (gusting as high as 50 MPH across the Central
Mntns, 45 MPH Arco Desert, and 20-35 MPH elsewhere), along with
possible weak cold frontal passages both days (especially into the
Central Mntns). Wind gusts have a 70% chance of exceeding 40 MPH
across the Arco Desert and Shoshone lava beds, as well as along the
Montana border. Gusts over 40 MPH are likely across the Central
Mntns, with a 50-60% chance of exceeding 50 MPH. The second low
passes to our north between Fri and Sun. Under this overall pattern,
occasional hints of SW monsoon moisture will continue to creep north
and produce generally isolated daily afternoon t-storms in some of
our mntn areas. The best coverage will be this afternoon. Storms may
produce gusty/erratic outflow winds over 45 MPH and small hail. Tue-
Wed, most areas will hold dry with isolated cells favoring the
srn/ern highlands. All of this said, chances of wetting
rain/meaningful QPF are VERY LOW regionwide.

Amid this warm, dry, breezy pattern, Tue and Wed afternoons continue
to stand out for potentially the best combination of gusty winds and
low RH, and thus the most critical fire wx conditions over the
largest area. After extensive coordination with all regional
interagency fire dispatch centers, the Great Basin GACC, surrounding
NWS offices, and deployed IMETs, fuels have been determined to be
critical over Zones 425 and 410, and approaching critical over Zones
475, 476, and 427, and we have issued our first RED FLAG WARNING of
the season for Zones 476, 425, and 410 Tue where winds will be
solidly critical and RHs at or below 15% will develop across more
than half of each warned zone. Operating fire crews should also
continue to be mindful of the heat and potential for heat-related
illnesses. Conditions change very little for Wed and another RED
FLAG WARNING is expected, but by the numbers, confidence is a bit
lower in winds for Zone 425. With the potential for the warning
footprint to change, and for simplicity of messaging, we are holding
with just Tue for the warning for now and will reevaluate tomorrow
for Wed. We also note that overnight RH recovery into Wed AM may be
poor at higher elevations. No significant changes in the overall
pattern...or chances for better wetting rains...are currently
forecast for at least the next week if not beyond. 01

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from noon to 9 PM MDT Tuesday for IDZ052.

&&

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