Damaging Winds in Idaho, August 29, 2023

Area Forecast Discussion
National Weather Service Pocatello ID
223 PM MDT Tue Aug 29 2023

.SHORT TERM...Tonight and Wednesday
Potent shortwave trough sweeping through the region will push a
front through the region this afternoon and into the evening. Ahead
of the front, southerly winds have allowed temperatures to surge
into the 90s across a good portion of the lower valleys today.
Breezy conditions are being observed across a good portion of the
region and this should continue into the day tomorrow. A Lake Wind
Advisory continues across the American Falls Reservoir and thus far,
we remain below Wind Advisory levels elsewhere. In addition to the
winds, showers and thunderstorms will be possible, mainly focused
across the Central Mountains. Hi-res CAMs show this as the best area
to see impactful weather with gusty winds and small hail certainly
possible here with the strongest of storms. Not expecting the
activity to make it much further south but there is a very slight
chance of this occurring. Much cooler temperatures (10-15 deg
cooler) and breezy winds will continue across the region Wednesday
in the wake of the exiting trough sweeping east along the Montana
highline. Wind speeds approach advisory levels across the Arco and
Mud Lake region during the day with possible wind highlights needed
on the next forecast cycle. Winds will slowly diminish as we get
into the evening hours tomorrow. McKaughan

.LONG TERM...THURSDAY THROUGH NEXT TUESDAY...
Generally held with NBM and WPC guidance through the long-term
period with very few changes/tweaks made, as focus is on developing
critical fire weather and severe thunderstorm potential today along
with ongoing support to fire partners. Thursday still looks dry
between systems, before a fresh low pressure system drops south
along the PacNW coast, stalls briefly over Oregon/nrn California,
and then ejects inland (perhaps trending a bit later with that
ejection...Sun?...compared to what we were seeing this time
yesterday in the long-term models). Ahead of it, deep S/SW flow will
draw increasing moisture/PWATs northward into our region with
increasing chances of daily showers/t-storms from Fri onward,
especially Sun. Mon is starting to look very much like Sun as well
with a later final passage of the trough axis and attendant
potential end to precip. Temps will remain fairly cool through the
period given the expected cloud cover and precip chances. 01

&&

.AVIATION...
Breezy conditions expected to continue across the area through the
period as a strong frontal boundary moves through the region. KSUN
stands the best chance of seeing precip with this feature but can't
rule out something making it into the Snake Plain terminals as well.
For now, those are forecast to remain dry however. Breezy winds will
continue into the day tomorrow but CIGs and VSBYs shouldn't be an
issue so VFR conditions should prevail. McKaughan

&&

.FIRE WEATHER...
The latest data overnight and this morning continued to support
slightly drier and slightly breezier conditions this afternoon/eve
compared to what we were seeing in yesterday afternoon's guidance,
prompting expansion of the RED FLAG WARNING to now include Fire
Weather Zones 425, 427, and 410 through 9 PM this eve (with coverage
of sub-15 percent RHs and fuels status being the limiting factors
keeping other zones out of the warning despite critically gusty
winds regionwide). Winds will be out of the south ahead of the
approaching advertised cold front, shifting into the west-southwest
behind the front, with frontal passage (and thus the wind shift)
likely between 5 PM and 9 PM this evening depending on your exact
location. The overall duration of true meteorological Red Flag
conditions is a bit limited as it will take some time for winds to
increase this afternoon, and then RH values will moisten rapidly
this eve as diurnal temps drop and the fresh, cooler airmass begins
to advect in with the front, even as elevated winds continue into
the night. If any fires ignite, partners should bear in mind that
gusty post-frontal winds will continue beyond the 9 PM end time of
the warning. This system will also bring isolated t-storms to much
of the region this afternoon/eve, perhaps sct in coverage in Zones
475, 476, and 411. Storms will generally lean dry and gusty, and a
few may be strong to severe, particularly the further north you go
in the sct coverage areas mentioned above. High-res CAMs are
generally leaning pretty dry south of the central Mntns and Upper
Snake Highlands, but hard to completely rule out a couple showers or
storms along the front itself (10-15% chance) and we've broadbrushed
this potential with higher PoPs than advertised by the NBM. RHs will
improve slightly Wed/Thu with no storms currently expected
(continued quite breezy Wed for many areas), before a deep south
flow ahead of our next low pressure system transports increasing
moisture northward Fri into the weekend. Chances of daily showers/t-
storms will increase each day, with Sun/Mon looking the wettest. 01

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 9 PM MDT this evening for IDZ410-425-427.

Lake Wind Advisory until 9 PM MDT this evening for IDZ054.

&&

Special Weather Statement
National Weather Service Pocatello ID
335 PM MDT Tue Aug 29 2023

IDZ072-292230-
Sawtooth/Stanley Basin ID-
335 PM MDT Tue Aug 29 2023

...A line of thunderstorms will impact the Boundary Fire burn scar
in northwestern Custer County through 430 PM MDT...

At 331 PM MDT, Doppler radar was tracking a strong thunderstorm 27
miles northwest of Stanley, moving northeast at 30 mph.

HAZARD...Winds in excess of 45 mph and locally heavy rain.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Additional rainfall could potentially
         lead to flooding issues with the Boundary Fire burn scar as
         storms continue to track over the area.

Locations impacted include...
Dagger Falls and Seafoam Ranger Station.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Locally heavy rainfall is also occurring with this storm and may
lead to localized flooding as additional storms track over the area.

These storms may intensify, so be certain to monitor local radio
stations and available television stations for additional
information and possible warnings from the National Weather Service.

&&

LAT...LON 4461 11528 4462 11523 4463 11522 4462 11520
      4465 11517 4471 11514 4473 11515 4477 11509
      4474 11503 4474 11502 4472 11501 4473 11498
      4472 11495 4480 11483 4479 11483 4444 11509
      4444 11523 4451 11524 4453 11530 4458 11531
TIME...MOT...LOC 2131Z 190DEG 21KT 4457 11520

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...45 MPH

KB