Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 110838
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
238 AM MDT Thu Aug 11 2022

.SHORT TERM...Today through Friday Night.
Showers and thunderstorms developing across the Great Basin worked
north through the evening hours yesterday and continue to bring
scattered showers and isolated thunderstorms early this morning
across the Upper Snake Plain, Eastern Highlands, and along the
Wyoming border. Precipitation will continue to track north
throughout the morning hours with drier conditions and clearing
skies shortly after sunrise clearing southwest to northeast.
Substantial cloud cover overhead will mitigate much of the fog
concerns with only slight chances for patchy development across our
southern and eastern valley locations where skies begin to break up.

Situated between a broad ridge of high pressure across the central
United States and a closed upper level low off the Pacific Coast for
today, showers and afternoon convection will pick up between 12PM
and 2PM across the higher terrain outside of the Snake Plain. Storms
today will see a more favorable environment over yesterday with
clear skies later this morning helping to support sufficient
instability coupled with a supportive 0 to 6 km shear environment.
The Weather Prediction Center has placed all of southeast Idaho in
an excessive rainfall outlook with a marginal 5 percent risk for
exceeding flash flood guidelines with supportive PWATs around 150 to
200 percent of normal for this time of year above an inch
bringing sufficient moisture aloft into developing cells across
the forecast area. Gusty winds in excess of 40 to 50 mph, small
hail, and moderate to heavy rainfall will be associated with
stronger thunderstorms that develop this afternoon with that
threat continuing into tomorrow. After sunset tonight, showers and
storms will decrease in coverage and intensity with the potential
for lingering moisture and instability supportive of showers and
isolated thunderstorms south and east of the Snake Plain
overnight.

As the area of low pressure off the Pacific Coast continues to track
north for Friday, expect a similar environment for storms again
building off of the higher terrain for tomorrow afternoon with a
marginal excessive rainfall outlook in place, sufficient CAPE and
shear, and PWATs running 150 to 200 percent of normal. The
departing low pressure system will bring drier air across western
Idaho, shifting mountain thunderstorms further north and east for
the weekend as a result into the Central Mountains and along the
Montana, Utah, and Wyoming border regions. Temperatures through
the period will remain near normal in the 80s to low 90s as
synoptic winds remain less than 30 mph.

.LONG TERM...Saturday through next Thursday.
Showers and thunderstorms will continue, especially across the
southern and eastern highlands over the weekend. The models and
majority of cluster forecasts show the ridge flattening a bit, as
the low that`s been offshore weakens and lifts north into western
Canada. This will bring somewhat drier air into the central
mountains, helping reduce the chance of thunderstorms. Any storms
up north will be drier vs anything farther southeast, which still
may produce locally heavy rain. Beyond that, the models show the
ridge building back to the northwest. The question is how strong.
About 85 percent of the clusters show a stronger ridge, which
reflects the GFS and ECMWF doing the same and potentially cutting
a ridge off overhead by the middle of next week. The models trying
to suppress the amount of thunderstorms, although not completely.
It is likely some amount of moisture is stuck rotating around or
even sneaking into the center of the ridge. The Blend of Models
shows this, although it might be a bit overzealous. We left what
the Blend was showing with some chance of showers and
thunderstorms across central and eastern Idaho.

&&

.AVIATION...For the 12Z TAFS through 12Z Friday.
Rain and storms moved through KPIH, KIDA, and KDIJ in the early
morning hours, but we are expecting some dry time at all sites
between about 09-18Z Thursday. With monsoonal moisture still in the
area, pop up showers and storms are possible again after 20Z.
Overall, VFR conditions are expected, though any storm that passes
over a terminal could drop visibility to MVFR conditions for a
time.

&&

.FIRE WEATHER...
After an active evening and overnight where we saw lightning,
wind and for many...beneficial rainfall...we will see a lull in
things this morning. By afternoon, the next round of showers and
thunderstorms will kick off. The focus appears to be across the
central mountains and southeast highlands (413). We will see lower
coverage of thunderstorms elsewhere, with actually a less than
10% chance across the Magic Valley and Craters of the Moon. The
concern is that the current forecast has more of a mix of wet and
dry storms (only pockets of 30-40% of wetting rains) this
afternoon and evening. We will have to see if this is underdone
based on areas seeing quite a bit of rain in the past 24 hours and
with still a big push of monsoon moisture across central and
eastern Idaho. We will also likely see gusts over 30 mph with some
storms. We may need to consult with our partners and see with the
drop in potential rainfall if we need to go for any critical fire
weather headlines later today. We should see another decrease in
activity overnight, although we might see a few showers remain
across zone 413 by sunrise. More showers and thunderstorms develop
by early afternoon Friday. Everyone is expected to see at least
isolated storms tomorrow, but higher coverage again will reside
over the central mountains and southeast highlands (413). There
appears to be a better chance of wetting rains across the central
mountains (30-40%) and from the Big Holes south across zone 413
(40-50%). Elsewhere, the risk of heavier rainfall is much
lower...but not zero either. For the weekend, better moisture ends
up getting pushed southeast a bit...away from the central
mountains. While we are still expecting a few storms up there,
they will be more isolated and definitely trending toward the dry
side. This even appears to be the case across the Snake Plain and
Magic Valley. Better chances remain across zones 411, 413 and 427.
These storms will also tend to be a mix or more wet than dry. The
potential for showers and storms continues into next week.

&&

.AIR QUALITY...
Recent fire activity has created adverse air quality conditions
across the upper valley for which the Idaho DEQ has issued an Air
Quality Advisory. This will likely be a day-to-day product
issuance given the unpredictable nature of wildfire smoke
production.

&&

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

&&

$$

www.weather.gov/Pocatello
www.facebook.com/NWSPocatello
www.twitter.com/NWSPocatello

SHORT TERM...MacKay
LONG TERM...Keyes
AVIATION...AMM/Keyes
FIRE WEATHER...Keyes
AIR QUALITY...Huston


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