Wind Advisory 24, NWS Pocatello, ID

Area Forecast Discussion
National Weather Service Pocatello ID
1018 AM MDT Fri Aug 26 2022

.UPDATE...A line of isolated showers and thunderstorms are
occurring from Carey to Grays Lake currently. Updated the
forecast to include these for this morning. Still expect isolated
showers and thunderstorms this afternoon along the Wyoming border,
especially the Bear Lake/Caribou Highlands.
Wyatt

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.PREV DISCUSSION... /issued 356 AM MDT Fri Aug 26 2022/

SHORT TERM...Today and Saturday.
As the upper trough continues to lift northeastward through Montana
into Canada today, drier air will move into the region under zonal
flow.  Only slight chances for isolated thunderstorms will exist
this afternoon and evening across the upper Snake River Plain and
eastern and southeastern highlands.  Convection looks to start
around 2 pm and work eastward into Wyoming, with all activity over
for our CWA by around 8 pm.  Today will be breezy, with sustained
winds reaching just over 20 mph and gusts close to 30 mph possible.
After several days of deterministic models and ensemble clusters
showing various solutions regarding the low pressure system that
will move through tomorrow, latest model runs are starting to come
to a better consensus. The GFS is bringing the closed low through
the northern extent of the Idaho panhandle early tomorrow afternoon,
while the ECMWF features a much more shallow trough passing through
the region. With a tight pressure gradient over our CWA, this
feature will bring strong winds region-wide.  The ECMWF EFI (Extreme
Forecast Index) has the majority of our region highlighted for
stronger than normal wind speeds.  With NBM v4.0 winds too weak, we
have blended with NBM v4.1 to better reflect what wind speeds could
materialize tomorrow afternoon into the evening.  Sustained winds
could reach up to 30 mph and gusts around 40 mph, with highest
speeds across the high terrain of the Central Mountains and the
upper Snake Plain. Slight chances for showers and thunderstorms will
also return to much of the region as this low passes.  At this time,
wind speeds look like they will reach Wind Advisory criteria and
could potentially justify a Red Flag Warning. While minimum
humidities look to remain above 15% tomorrow with the exception of
a few locations, strong enough winds may prompt us to issue a Red
Flag Warning. Have opted to hold off for now considering the
recent discrepancies in model runs and let the next shift assess
as new data becomes available. Temperatures over the next two
days will run slightly above normal. Cropp

LONG TERM...Sunday through next Friday.
Models are lining up a little better in the extended, especially
the operational GFS and European. These models show a weak
low/shortwave passing through Montana and entering the Dakotas by
00z Monday with a ridge developing across our region. Most models
agree with this solution although about 40% of models are still
advertising a slower deeper trough hanging back across the
northern Great Basin during this time. As a result, the NBM is
holding on to some low chances rain chances for Sunday across the
high country. With the trend of good consensus between the 00Z
operational runs of the European and GFS, think we may see those
rain chances lower in future NBM runs. All models show the ridge
amplifying on Monday, although the operational GFS and European
have a weak shortwave trying to work up the western side of the
ridge Monday into Tuesday. This could throw a chance for storms
into the forecast for midweek if it verifies. But right now, most
of the clusters are showing a ridge-dominant pattern with the
shortwave weakening as it moves over the ridge. The consensus
shows that ridge further amplifying for late week with the extreme
forecast index offered by the ECMWF indicating extreme heat for
central and east Idaho for mid to late week. For example, about
2/3rds of the GFS members are advertising highs in the mid to
upper 90s for Pocatello late week. 13

AVIATION...Several HREF members show convection developing near
KSUN and across the upper Snake Plain and drifting east this
afternoon. Consequently, will continue to mention VCTS at KSUN,
KIDA, and KDIJ. HREF and NBM 4.1 shows wind gusts this afternoon to
near 20 kts at many sites so will include some wind gust mention as
well. 13

FIRE WEATHER...As the upper trough continues to lift northeastward
through Montana into Canada today, drier air will move into the
region under zonal flow. Isolated thunderstorms will still be
possible, with greatest chances across the upper Snake River
Plain, as well as Fire Weather Zone 413. Convective initiation
will likely occur around 2 pm and storms will work eastward into
Wyoming, with all activity expected to be outside of Idaho by
around 8 pm. Winds will also be breezy, with sustained winds
potentially reaching 20 mph and gusts up to 30 mph possible.
Tomorrow should be quite a bit windier region-wide though, as
models continue to sort out the details of an upper low moving
through Idaho tomorrow. As the pressure gradient tightens over us,
sustained winds up to around 30 mph and gusts around 40 mph are
likely, with highest speeds across the high terrain of the Central
Mountains and the upper Snake Plain. While minimum humidities
look to remain above 15% tomorrow with the exception of a few
locations, strong winds may be cause for issuance of a Red Flag
Warning tomorrow. Considering discrepancies in recent model runs,
have opted to hold off for now and let the next shift reassess as
more data becomes available. Cropp/13

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.PIH WATCHES/WARNINGS/ADVISORIES...
None.
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