Special Weather Statement, NWS Pocatello, ID

Area Forecast Discussion
National Weather Service Pocatello ID
151 PM MDT Fri Jul 16 2021

.DISCUSSION...Satellite imagery showing afternoon build-ups
beginning across higher elevations of East Idaho early this
afternoon. A few cells already developing into something the radar
can see, and expect development to continue for the next several
hours. Have maintained thunderstorm coverage in line with blend of
the high-res models for the afternoon, with coverage dropping off
after sunset. Dry low levels should be conducive for another round
of strong gust potential. One more shortwave feature rotates
through the Great Basin on Saturday, so East Idaho could see
another round of afternoon/evening thunderstorms, mainly across
southern portions of the region. Smoke has been less of a concern
with good air quality across much of the Snake Plain and areas
south. HRRR Smoke fields hold smoke to the central mountains, due
to both fires there and being within the trajectory of the smoke
from Oregon/California. Have allowed the HRRR smoke fields to
populate that portion of the forecast without broad-brushing
patchy values over the rest of the area. Moving into Sunday and
Monday, center of upper high anchors over southwest Wyoming. South
flow into East Idaho still indicative of a temperature increase.
Interestingly, models are still picking up on a bit of mid-level
moisture flow through the Great Basin for Sunday, and the 12Z NAM
now showing a few thunderstorms Sunday afternoon. Numerical
guidance still pushing 100+ temperatures for a large chunk of the
area, with overnight temperatures trending upwards as well.
Ensemble blends still trending below guidance, so kept the numbers
a little above the blend, but below the higher guidance values.
The additional moisture, and onset of the deeper monsoon moisture
for Monday are a concern for limiting the top end of temperature
potential. Heat Risk still quite elevated, so will keep the
Excessive Heat Watch in place. Speaking of the monsoonal moisture,
ensemble PWAT values spike up sharply in most if not all members
starting Monday. Thunderstorm activity is expected to become more
widespread through the middle of the week, potentially continuing
through the end of the week as there is not much in the way of
features to push the moisture stream away to the east.
Temperatures are expected to moderate somewhat for Tuesday and
beyond. DMH

&&

.AVIATION...
Have vicinity thunder at DIJ, BYI and PIH.  Think coverage not as
widespread as yesterday but will still have isolated development.
Only have smoke visibility restrictions at SUN but keep at 6 statue
miles.  Other sites seem to have mainly gone to 10 miles or more for
the most part and kept no visibility restrictions any longer.  Winds
generally light and 10 knots or less unless near any thunderstorm
outflow.
GK

&&

.FIRE WEATHER...
High Haines index red flag warning is in effect through tonight in
zones 475 and 422.  Mud Lick does not look as active today.   Did
not extend the warning so will let next shifts decide on Saturday
into the weekend.  Expect isolated thunderstorms today with some
possible outflow over 30 mph but should not be as widespread as
yesterday.   Hot conditions will intensify over the weekend with the
persistent Haines index of 6 continuing.  Next week monsoonal flow
will be the main feature and the threat for thunderstorms will be
more extensive with a better chance for precipitation.
GK

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Watch from Sunday afternoon through Monday
evening for IDZ051>059.

Red Flag Warning until 7 AM MDT Saturday for IDZ422-475.

&&

Special Weather Statement
National Weather Service Pocatello ID
410 PM MDT Fri Jul 16 2021

IDZ057>059-162300-
Franklin/Eastern Oneida Region ID-Marsh and Arbon Highlands ID-
Raft River Region ID-
410 PM MDT Fri Jul 16 2021

...SIGNIFICANT WEATHER ADVISORY FOR WESTERN ONEIDA AND SOUTH CENTRAL
POWER COUNTIES UNTIL 500 PM MDT...

At 410 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from 12 miles south of Rockland to 8 miles north of
Juniper. Movement was east at 10 mph.

Half inch hail and winds in excess of 40 mph will be possible with
these storms.

Locations impacted include...
Holbrook and Roy.

LAT...LON 4256 11260 4201 11260 4210 11299 4244 11299
TIME...MOT...LOC 2210Z 263DEG 8KT 4239 11292 4213 11292

Valle

Special Weather Statement
National Weather Service Pocatello ID
436 PM MDT Fri Jul 16 2021

IDZ058-062-162315-
Marsh and Arbon Highlands ID-Blackfoot Mountains ID-
436 PM MDT Fri Jul 16 2021

...WINDS TO 50 MPH...SMALL HAIL AND HEAVY RAIN FOR WEST CENTRAL
CARIBOU AND EAST CENTRAL BANNOCK COUNTIES UNTIL 515 PM MDT...

At 434 PM MDT, Doppler radar was tracking a strong thunderstorm near
Lava Hot Springs, moving north at 10 mph.

Wind gusts up to 50 mph, small hail and locally heavy rain will be
possible with this storm.

Locations impacted include...
Lava Hot Springs, Chesterfield Reservoir, Chesterfield and Bancroft.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

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.

&&

LAT...LON 4256 11192 4262 11214 4294 11211 4280 11165
TIME...MOT...LOC 2234Z 200DEG 10KT 4267 11200

Keyes

Special Weather Statement
National Weather Service Pocatello ID
440 PM MDT Fri Jul 16 2021

IDZ054-055-058-162330-
Eastern Magic Valley ID-Marsh and Arbon Highlands ID-
Lower Snake River Plain ID-
440 PM MDT Fri Jul 16 2021

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN BANNOCK...CENTRAL
POWER AND SOUTHWESTERN BINGHAM COUNTIES UNTIL 530 PM MDT...

At 439 PM MDT, strong outflow winds from a collapsed thunderstorm
was reported near American Falls, moving north at 30 mph.

Winds in excess of 40 mph will be possible with this storm.

Locations impacted include...
American Falls, Neeley, American Falls Reservoir, Aberdeen,
Springfield, Pingree, Pocatello Airport and Sterling.

Boaters can expect a sudden increase in waves and very choppy waters
which will result in hazardous boating conditions. Boaters are urged
to seek safe harbor if possible.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If on or near American Falls Reservoir, Move to safe shelter now! Do
not be caught on or near the water. Gusty winds and choppy waves are
likely.

&&

LAT...LON 4268 11271 4272 11295 4319 11287 4313 11251
TIME...MOT...LOC 2239Z 192DEG 25KT 4278 11281

Valle