High Wind in Idaho, November 1, 2017

Area Forecast Discussion
National Weather Service Pocatello ID
1032 AM MDT Wed Nov 1 2017

.UPDATE...

Expanded the wind advisory to include the upper Snake Highlands.
Observations from around Driggs to St. Anthony are near wind
advisory this morning, with the strongest winds yet to come.
Latest MAV/MET guidance solidly supports the high wind warning
across the Snake Plain, made minor adjustment to wind speeds
there. Still think wind advisory possible in some of the central
mountain areas, for instance around Mackay, Challis and perhaps
Hailey. Will continue to monitor winds in those areas, and may
expand the advisory there this afternoon.

Valle

&&

.PREV DISCUSSION... /issued 317 AM MDT Wed Nov 1 2017/

SHORT TERM...Through Thursday night. Strong, gusty winds
anticipated today across SE Idaho, strongest across the Snake
Plain and Arco Desert. Debated a Wind Advisory vs. High Wind
Warning for the Snake Plain/Arco Desert and ultimately settled on
a High Wind Warning for zones 20 and 21 which includes Pocatello,
Idaho Falls and the Arco Desert. Winds at the surface have been
stronger than depicted all evening into the early overnight hours
vs. all model guidance as vertical mixing remains efficient --
transporting stronger winds above the surface to the ground.
Pockets of blowing dust are anticipated along I-15 and adjacent
Highways today with the lowest visibility in the Roberts area
north of I-15. Strong crosswinds will also be a consequence,
particularly on northwest to southeast oriented routes. The
combination of pockets of low visibility and strong crosswinds
will make travel hazardous. Strongest winds are expected from
roughly Noon through 5 PM this afternoon and will be from the
Southwest. Latest indications suggest impactful wind speeds may
develop well before the Noon hour. Winds are expected to
gradually diminish after Sunset and should produce limited impacts
after 9 PM. Breezy conditions are again expected on Thursday into
early Thursday evening which may cause some difficult driving
conditions.

In terms of precipitation, rain and snow showers are expected to
develop this afternoon across the Sawtooths, and Pashimeroi ranges
eastward along the Divide to Island Park with this activity
expected to gradually shift southward through this evening. Snow
is expected to be confined to elevations above roughly 6,500 ft
elevation through Sunset but are expected to fall closer to 6,000
feet elevation overnight as precipitation is expected to linger
from Island Park southward along the Wyoming border in moist,
westerly upslope flow. Thus, locations such as Pine Creek Pass
and other routes above 6,000 feet elevation may see some slushy
driving conditions develop. AD/DMH

LONG TERM...Friday through Wednesday. Active trough shifting into
the region by Friday with precipitation spreading across most of
East Idaho. Main cold air remains west, so snow levels elevated
prior to frontal passage late Saturday/Saturday night. Winds again
expected to increase along/behind the front for locally strong/gusty
winds Saturday afternoon. Precipitation shield shifts southeast
along with the front, so even with temperatures cold enough to
support snow at most valley floors - including the Snake Plain - by
Sunday, much of the precipitation should be moved out of the region
by then. Models depict brief break in the activity with dry slot
shifted across the region late Sunday into Sunday night. Secondary
shortwave trough quickly shifts into the region late Sunday night
into Monday. Moisture much more limited with this secondary event,
but temperatures do look cold enough to support snow to valley
floors, especially at night. Ridge rebounds Tuesday into Wednesday
for dry conditions, at least per the GFS. ECMWF much more amplified
with secondary trough Monday, dropping it deeper into the Great
Basin, resulting in slower exit into Tuesday leaving ridge for
Wednesday. DMH

AVIATION...Mid to high cloud cover streaming across the region
today. Most sites expected to remain VFR and generally dry through
daylight hours. Exception could be KDIJ, with some showers expected
to develop by afternoon along WY border. Precipitation could spread
a little farther overnight, mainly affecting both KDIJ and KSUN with
a low confidence possibility of even reaching KIDA after 06Z.
Otherwise winds remain the main concern and impact for today. Very
strong winds expected to develop, and already showing signs of
strengthening early this morning. Sustained winds well over 30kts at
expected at most East Idaho terminals, except KSUN where 20-25kts
will be expected. Gusts, particularly at KPIH/KIDA may exceed 45kts
this afternoon. Will likely be adding LLWS with early morning
terminal issuance until 16-17Z when winds mix and fully strengthen.
Given strength and direction of winds above the surface, LLWS may be
appropriate for the entire day, especially at KPIH and KIDA.
Significant drop in winds are expected around 03Z tonight. DMH

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 9 PM MDT this evening for IDZ020-021.

Wind Advisory until 9 PM MDT this evening for IDZ017-019-022-023.

&&