Hail and Damaging Winds in Idaho, July 1, 2023

Area Forecast Discussion
National Weather Service Pocatello ID
133 PM MDT Sat Jul 1 2023

.SHORT TERM...Tonight through Sunday night.

A ridge of high pressure centered over southern California is trying
to build into our region this afternoon. This ridge is responsible
for warming temperatures across the region. Meanwhile, a shortwave
trough is trying to move over the top of the ridge through eastern
Idaho this afternoon. The HREF members are aligning more and showing
a broken line of storms emerging from the Lemhi/Lost River valleys
this afternoon. This line will advance east across the upper Snake
Plain and upper Snake Highlands late this afternoon and evening.
Some of the HREF members are showing that some of these storms could
be robust, marginally severe even. Strong gusty winds and marginally
severe hail are certainly possible. Looks like most of this line
moves east into Wyoming around 7pm, although a few isolated storms
remain possible behind the line through 10pm.

On Sunday, temperatures look a couple degrees warmer with 90s
certainly possible across the lower valleys. For the mid and upper
Snake Plain, looking around a 30% chance for 90 or above while the
eastern Magic Valley has about a 60% chance. Isolated thunderstorms
look possible once again on Sunday, but this time the focus is
across the south hills into the southeast highlands, potentially as
far north as the Magic Valley into the lower Snake Plain. There's
not a strong focus for the storms, appears to be mainly moisture
working around the northern periphery of the high pressure area.
These storms look mainly diurnally generated during the heat of the
day and should dissipate in the early evening. Although, the severe
parameters aren't lining up as well on Sunday, a rogue strong wind
gust along with some small hail remains possible. Outside of storms,
does appear a bit gusty tomorrow afternoon with sustained winds
around 15 mph with gusts near 25 mph possible. This is close to lake
wind criteria for American Falls Reservoir, but most likely staying
just under.

13

.LONG TERM...MONDAY THROUGH NEXT SATURDAY...
The coming week will be characterized by a ridge of high pressure
over the SW US, while a low pressure system marches east across
Canada. This system will tend to flatten the nrn extent of the
ridge, increase winds, and bring an uptick in showers/t-storm
activity, especially Mon and Tue afternoons, perhaps returning again
Fri/Sat as we potentially see a second area of low pressure approach
the PacNW coast. Otherwise, expect the ridge to supply some heat,
with highs in the 80s/lower 90s for most population centers. Mon is
currently the warmest day, with a 60% chance of exceeding 90 degF at
Burley, Pocatello, and Idaho Falls. Perhaps good news for outdoor
festivities...high temps on Independence Day are currently forecast
to be a few degrees cooler...generally topping out in the 80s. 01

&&

.AVIATION...Main concern for aviation this afternoon/eve
continues to be potential for isolated to scattered t-storms. Have
expanded VCTS to all TAF terminals, and adjusted start/end timing
based on the consensus of the 12z HREF suite and the 15z HRRR.
Confidence on overall timing is moderate to high. We are seeing
signs from a few of the high-resolutions CAM runs that either
several strong cells...or cells congealing into a line...may try
to impact KIDA (22- 24z/4-6pm) and KDIJ (23-01z/5-7pm) in an
environment characterized by steep lapse rates and strong DCAPE
supportive of strong sfc winds. If confidence increases, will try
to introduce these impacts to the TAFs via amendments with wind
gusts in excess of 50 MPH/43kts possible, predominantly out of the
WNW. Current probability of this taking place is about 40%. A
severe t-storm cannot be ruled out, although best chance will be
north of both terminals. Outside of t- storms, slightly breezy
conditions are expected this afternoon/eve, although with wind
gusts generally 20kts or less. A westerly runway crosswind is
likely after about 21z/3pm at KSUN at 10g20kts, possibly weakening
after 01z (and we'll see that again tomorrow afternoon).
Regionwide, t-storm outflows could travel long distances and alter
the currently forecast synoptic wind picture...another thing
we'll need to watch. Model consensus is strong that everything
will die by 03-04z/9-10pm this eve , with skies clearing and
benign wx overnight and throughout Sun AM. - KSmith

&&

.FIRE WEATHER...Isolated to scattered thunderstorms this afternoon
will diminish this evening. Strong gusty outflows are very possible
near thunderstorms. Conditions look a couple degrees warmer and with
lower humidity for Sunday. Although isolated storms will remain
possible across Idaho fire zones 427 and 413. Expect breezy
conditions on Sunday as well with gusts to 25 mph possible in many
areas.

13

&&

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

Special Weather Statement
National Weather Service Pocatello ID
217 PM MDT Sat Jul 1 2023

IDZ052-068-069-012100-
Arco/Mud Lake Desert ID-Lost River Range ID-Lost River Valleys ID-
217 PM MDT Sat Jul 1 2023

...A STRONG THUNDERSTORM WITH POSSIBLE WIND AND HAIL DROPPING OUT OF
THE BIG LOST RIVER VALLEY INTO NORTHERN PORTIONS OF IDAHO NATIONAL
LABORATORY...

At 215 PM MDT, Doppler radar was tracking a strong thunderstorm
just north of Arco, moving east at 25 MPH.

HAZARD...Wind gusts up to 50 MPH and penny size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Arco, Central Inl, Southwest Inl, Moore and Butte City.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

This storm 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.

If you observe hail or wind damage, please report your observations
to the National Weather Service in Pocatello via phone, email, or
social media, when it is safe to do so.

&&

LAT...LON 4364 11347 4380 11340 4377 11279 4347 11295
TIME...MOT...LOC 2015Z 281DEG 24KT 4372 11330

MAX HAIL SIZE...0.75 IN
MAX WIND GUST...50 MPH

KSmith