Special Weather Statement, NWS Pocatello, ID

Area Forecast Discussion
National Weather Service Pocatello ID
223 PM MDT Wed Jul 21 2021

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT...
A dome of high pressure centered over the 4-Corners region continues
to wrap monsoon moisture into our SE Idaho forecast area with it's
clockwise flow. Today, isolated t-storms have already initiated
across the Central Mntns, MT border, and Cassia County/Raft River
region, and these are the areas that will remain favored for
activity, with perhaps a few cells escaping into the Snake Plain
this eve. OVERALL, coverage looks a bit more isolated today compared
to yesterday, and despite continued monsoon moisture, PWATs have
eased slightly today into the 0.5" to 0.9" range per the HREF
ensemble mean, which MIGHT take the edge off some of the heavy
downpours and localized flood potential. Still, stronger cores will
need to be monitored for small hail and heavy rain, with lightning
of course a concern for new fire starts. Gusty wind potential, while
not zero, is low given continued dew points in the upper 40s to mid
50s (so we've lost the ideal dry-microburst regime we normally see
here in SE Idaho which would be characterized in part by very dry
low-level air below 600-500mb). Thurs, one more round of afternoon/
eve t-storms is expected (with perhaps even a few isolated showers/t-
storms during the AM), with the high-res CAMs suggesting slightly
greater coverage again than today and HREF mean PWATs again surging
to 0.8" to 1.2" for most of our CWA (well above average and
potentially supporting rainfall rates in excess of 0.50" per hour).
Thus, lightning and torrential rainfall/localized flash
flooding/debris flows will return as the core concerns tomorrow,
with hail also possible in stronger cores. Have added mention of
heavy rainfall to the grids. For now we've held t-storm coverage at
isolated in the forecast, but we may need to nudge to scattered for
portions of the srn/ern highlands with resultant potential for a Red
Flag Warning (see the FIRE WEATHER section below for more on fire wx
concerns). Our pattern finally starts to change Fri as a trough
crossing the nrn Rockies into the nrn Plains Thurs/Fri "flattens"
the ridge and shunts monsoon moisture back to our south with more of
a zonal westerly flow taking over across Idaho, setting us up for 3
days of largely dry wx lasting through the weekend. - KSmith

.LONG TERM...SATURDAY THROUGH NEXT WEDNESDAY...
After a dry weekend with high temps topping out about 5-8 degrees
above normal (in the upper 80s to mid 90s), models nudge the srn
high pressure dome a bit further east and amplify it's ridge,
putting SE Idaho back into a SW flow on the west side of the ridge
and bringing monsoon moisture back northward, particularly starting
Tue. High temps are also expected to nudge back toward the upper 90s
Mon, and potentially Tue depending on cloud cover with a response
seen in the ECMWF EFI (Extreme Forecast Index) both days.
Accordingly, the 8-14 Day CPC outlook continues to favor above
normal temps and above normal precip. - KSmith

&&

.AVIATION...
Isolated to scattered thunderstorms remain forecast for all of East
Idaho, and have maintained VCTS at all terminals through the evening.
High resolution model trends maintain showers overnight for
KPIH/KIDA/KBYI/KDIJ. At this point, do not expect any of this
activity to stay developed to thunderstorms overnight, but it
won't be out of the question. Better chances for thunderstorm re-
development exist for these sites after sunrise Thurs AM. - DMH

&&

.FIRE WEATHER...
Isolated to scattered thunderstorms remain the focus for East Idaho
fire concerns today and Thursday. Red Flag Warnings continues for
the central mountain zones through this evening, with isolated
coverage elsewhere. Showers continue overnight mainly Snake Plain
and south/east, though would not be surprised to see a lightning
strike or two. Better chances for development into stronger cells
occurs during the day Thursday, along with potential for locally
heavy downpours. Drier air is beginning to work into the region from
the west, so we're seeing isolated thunderstorms in the central
mountains and Snake Plain. The dry push shift across most of the
region beginning Friday, with much of the monsoonal flow pushed
south and east of East Idaho. Thus expect humidities to trend drier
and temperatures to trend upward...again... through the weekend into
early next week. The next potential for thunderstorms across the
region looks to be Tuesday, with better chances into midweek as the
upper high strengthens over the central Rockies, pulling monsoonal
moisture north through the Great Basin once again. - DMH

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 9 PM MDT this evening for IDZ475-476.

&&

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Special Weather Statement
National Weather Service Pocatello ID
459 PM MDT Wed Jul 21 2021

IDZ055-056-212345-
Eastern Magic Valley ID-Southern Hills/Albion Mountains ID-
459 PM MDT Wed Jul 21 2021

...THUNDERSTORM SOUTH OF OAKLEY ALONG THE UTAH BORDER MOVING
NORTHEAST TOWARD CITY OF ROCKS THROUGH 545 PM MDT...

At 454 PM MDT, Doppler radar was tracking a thunderstorm 13 miles
south of the Oakley Reservoir, moving northeast at 15 mph.

Brief moderate rain and wind gusts to 40 mph are possible with this
storm as it moves northeast toward City of Rocks. Firefighters
working the South Carson Fire should be prepared for southerly
outflow wind gusts from this system through 600 PM MDT.

Locations impacted include...
Almo and City Of Rocks.

LAT...LON 4199 11406 4224 11382 4206 11356 4199 11368
TIME...MOT...LOC 2254Z 223DEG 11KT 4197 11393

Huston

Special Weather Statement
National Weather Service Pocatello ID
504 PM MDT Wed Jul 21 2021

IDZ057>059-212345-
Franklin/Eastern Oneida Region ID-Marsh and Arbon Highlands ID-
Raft River Region ID-
504 PM MDT Wed Jul 21 2021

...THUNDERSTORM SOUTHEAST OF MALTA MOVING NORTHEAST TOWARD RURAL
SOUTHWEST POWER COUNTY THROUGH 545 PM MDT...

At 501 PM MDT, Doppler radar was tracking a thunderstorm 10 miles
southeast of Malta, moving northeast at 20 mph.

Brief heavy rain and wind gusts to 40 mph are possible with this
storm as it crosses Interstate 84 near Sublett and moves northeast
into rural southwest Power County through 545 PM MDT.

Locations impacted include...
Roy, Sweetzer Summit and Sublett Reservoir.

LAT...LON 4212 11317 4224 11333 4255 11296 4234 11273
TIME...MOT...LOC 2301Z 230DEG 16KT 4225 11318

Huston

Special Weather Statement
National Weather Service Pocatello ID
514 PM MDT Wed Jul 21 2021

IDZ073-075-220000-
Wood River Foothills ID-Sun Valley Region ID-
514 PM MDT Wed Jul 21 2021

...THUNDERSTORM NORTHEAST OF FAIRFIELD MOVING NORTHEAST TOWARD
KETCHUM THROUGH 600 PM MDT...

At 512 PM MDT, Doppler radar was tracking a thunderstorm 7 miles
northeast of Fairfield, moving northeast at 30 mph.

Brief heavy rain and wind gusts to 40 mph are possible with this
storm as it moves northeast into Ketchum around 600 PM MDT.

Locations impacted include...
Hailey, Ketchum and Sun Valley.

LAT...LON 4383 11447 4368 11416 4335 11453 4340 11453
      4340 11455 4343 11455 4346 11451 4348 11451
      4349 11452 4349 11453 4351 11457 4352 11458
      4353 11460 4356 11459 4357 11463 4360 11466
TIME...MOT...LOC 2312Z 214DEG 27KT 4340 11466

Huston

Special Weather Statement
National Weather Service Pocatello ID
519 PM MDT Wed Jul 21 2021

IDZ054-055-057-058-220015-
Eastern Magic Valley ID-Marsh and Arbon Highlands ID-
Raft River Region ID-Lower Snake River Plain ID-
519 PM MDT Wed Jul 21 2021

...THUNDERSTORM NEAR NEELEY MOVING NORTHEAST TOWARD AMERICAN FALLS
THROUGH 615 PM MDT...

At 516 PM MDT, Doppler radar was tracking a thunderstorm near
Neeley, moving northeast along the southern periphery of
Interstate 86 at 10 mph.

Brief heavy rain and wind gusts to 40 mph are possible with this
storm as it moves northeast toward American Falls through 615 PM
MDT. Fire crews working the Lusk Fire may also experience northerly
outflow winds as this system passes by to the north.

Locations impacted include...
American Falls, Neeley, western American Falls Reservoir, Rockland,
Fort Hall Bannock Creek Lodge and Massacre Rocks.

LAT...LON 4253 11291 4265 11309 4294 11282 4276 11254
TIME...MOT...LOC 2316Z 222DEG 11KT 4265 11294

Huston