High Wind in Idaho, April 10, 2021

Area Forecast Discussion
National Weather Service Pocatello ID
242 AM MDT Sat Apr 10 2021

.SHORT TERM...Through Monday night. The second high wind event in
as many days remains on the horizon across eastern Idaho today.
The setup is very similar to our Thursday wind event, with subtle
differences. Two of these differences include slightly stronger
700mb winds across the Upper Snake Plain as well as slightly
more robust low-level lapse rates, which should lead to slightly
better boundary layer mixing. The next result will be winds
slightly stronger than what we saw on Thursday, especially from
Craters of the Moon northeast through the INL towards Idaho Falls
and Rexburg. Forecast soundings indicate 60kts of wind as low as
700mb (5,000ft AGL) by 00Z (6PM MDT) this evening. Unidirectional
west-southwest winds through the boundary layer will align with
terrain, and this should cause a swath of 60-70 mph wind gusts
from Craters of the Moon through INL and the Idaho Falls and
Rexburg areas, peaking around the aforementioned 6PM MDT
timeframe. Have also increased the blowing dust wording to
widespread in the Roberts area. These have been the only notable
changes to the going forecast. These winds will be caused by an
amplifying (strengthening) shortwave trough as it passes just to
our north across Montana and the Idaho Panhandle. The associated
mass adjustment and tightening pressure gradient will lead to the
increasing winds. Dry slot/stratospheric intrusion already noted
on water vapor imagery early this morning as it punches into
Washington state. This will translate south and east across
eastern Idaho this afternoon and lead to a rapid ramp-up in winds
by late-morning. One other subtle difference compared to
Thursday's event is that winds should linger a few hours longer
into the evening, but the current 11PM end time for the High Wind
Warning and Wind Advisories looks good. Have added the south
hills, Albion mountains, Rafter River Region, Blackfoot Mountains,
Marsh and Arbon highlands as well as the Teton Valley to a Wind
Advisory as well. Many of these areas experienced Wind Advisory
level winds on Thursday, and there's no forecast guidance to
suggest otherwise for today's system. Impacts will be very similar
to Thursday as well, with near zero visibility in blowing dust
expected in the Interstate 15 stretch from Idaho Falls to Roberts,
as well as a significant reduction in visibility along Interstate
15 north of Fort Hall, Interstate 86 from Pocatello to American
Falls and Highway 39 between American Falls and Aberdeen. In
addition, tree and powerline damage is once again expected,
especially across the northern Snake Plain where winds will be
stronger. Secure any loose, lightweight objects and expect very
strong crosswinds, especially on north-south oriented routes.

Saturday evening, winds will shift to the north and northwest
across the northern Snake Plain, just like what was observed on
Thursday. This wind shift will then translate south and west down
the Snake Plain through the late evening hours. Areas ahead of
(south of) the boundary will see the strong southerly winds
continue with only a gradual downturn in the winds until the
passage of the surface boundary. A few snow showers will be
possible from late afternoon through evening with the passage of
the boundary, mainly across the central Idaho mountains, Montana
border region and Island Park south to Palisades.

Cool northwest flow will be in place across the region on Sunday
with light north to northeast winds in place, a welcome change to
Saturday's wind. By Monday, another low pressure system will be
taking shape across the Pacific Northwest. This low is expected to
form across eastern Oregon and Washington Monday night. A gradual
development of rain and snow showers is expected to begin Monday
night as the low strengthens and approaches. North to northeast
winds will gradually strengthen Monday and Monday night as a
result, with a continued increase in north to northeast winds
into Tuesday. More on that below.

AD

.LONG TERM...Tuesday through Saturday. Much of the NW US will be
dominated by a closed upper low at least through Thursday night.
We'll be looking at unsettled weather through that period.
Deterministic models differ slightly with the location of the low
center and the coverage of precip. The 00Z GFS appears to be the
wettest with the low in closer proximity to east Idaho. Ensembles
and their clusters provide little clarity to the forecast with large
spreads in snowfall amounts. Blended guidance keeps best snowfall
over the Southeastern Highlands. Boosted the winds Tuesday with GFS
MOS guidance pushing us towards advisory criteria--and particularly
impactful to American Falls Reservoir given the northeasterly wind
direction. Temperatures should remain well below climatology while
the upper low is in the proximity. Models show a trend towards drier
weather close to the end of the week. Cyclonic flow aloft should
still be in place, but less moisture will be available for precip.
Hinsberger

&&

.AVIATION...Another robust cold front will make its way through
southeast Idaho late this morning to early afternoon. There is
little chance of precipitation, but winds will once again be gusting
close to 50 mph in the Snake Plain. Southwest winds will be
particularly strong in the afternoon, tapering off in the evening.
Models show signs the winds will shift down-valley after midnight.
This will be around the time that DIJ may see its best chance for
precip. Greatest wind impacts will be from 18Z to 03Z.
Hinsberger

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from 11 AM this morning to 11 PM MDT this
evening for IDZ052-053.

Wind Advisory from 11 AM this morning to 11 PM MDT this evening
for IDZ051-054>058-062-065.

&&