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.

&&

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE POCATELLO ID
1151 AM MDT WED JUL 21 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0215 PM     TSTM WND GST     9 N BLACK PINE          42.15N 112.99W
07/20/2021  M53 MPH          ONEIDA             ID   DEPT OF HIGHWAYS

            ITD RWIS STATION ITD47 - I-84 JUNIPER
            INTERCHANGE.

0414 PM     HAIL             3 W GRACE               42.58N 111.79W
07/20/2021  E0.25 INCH       CARIBOU            ID   TRAINED SPOTTER

            PEA-SIZED HAIL AND HEAVY RAIN (EST 0.60 IN
            IN 15 MIN).

0430 PM     HAIL             4 W SODA SPRINGS        42.66N 111.66W
07/20/2021  E0.50 INCH       CARIBOU            ID   PUBLIC

            PUBLIC REPORTS HAIL ESTIMATED AT SLIGHTLY
            LARGER THAN PEAS AND VERY HEAVY RAIN WITH
            MINOR FLOODING ALONG US-30 BETWEEN ALEXANDER
            AND THE WESTERN SODA SPRINGS CITY LIMIT.
            TIME ESTIMATED BASED ON REPORT AND RADAR.

0442 PM     HEAVY RAIN       1 WSW SODA SPRINGS      42.65N 111.61W
07/20/2021  E0.50 INCH       CARIBOU            ID   TRAINED SPOTTER

            HEAVY RAIN. APPROXIMATELY 0.50 IN 15 MIN.

0528 PM     HAIL             2 NNW TETONIA           43.84N 111.17W
07/20/2021  E0.50 INCH       TETON              ID   PUBLIC

            ESTIMATED HALF-INCH HAIL COVERING THE ROAD.
            BETWEEN TETONIA AND FELT. TIME ESTIMATED
            BASED ON RADAR.

0549 PM     HEAVY RAIN       3 NE TETONIA            43.85N 111.13W
07/20/2021  E0.75 INCH       TETON              ID   TRAINED SPOTTER

            HEAVY RAIN. ESTIMATING 0.75 IN IN 45 MIN.

1159 PM     HEAVY RAIN       1 SE REXBURG            43.81N 111.77W
07/20/2021  M0.70 INCH       MADISON            ID   TRAINED SPOTTER

            RAINFALL TOTAL FOR TUESDAY 07-20-2021. NEAR
            THE INTERSECTION OF E 7TH ST AND S 4TH ST.

1159 PM     HEAVY RAIN       2 SW TETONIA            43.80N 111.18W
07/20/2021  M0.60 INCH       TETON              ID   PUBLIC

            PRIVATE WEATHER STATION. TOTAL FOR TUESDAY
            07-20-2021. 0.57 INCHES OF THIS ACCUMULATION
            FELL IN 30 MINUTES BETWEEN 509 PM AND 539
            PM.

1159 PM     HEAVY RAIN       1 WNW FELT              43.88N 111.20W
07/20/2021  M0.56 INCH       TETON              ID   PUBLIC

            PRIVATE WEATHER STATION. TOTAL FOR TUESDAY
            07-20-2021, JUST WEST OF FELT.

1159 PM     HEAVY RAIN       6 SSW HENRY             42.82N 111.56W
07/20/2021  M0.46 INCH       CARIBOU            ID   PUBLIC

            PRIVATE WEATHER STATION ALONG ID-34 JUST
            NORTH OF BLACKFOOT RIVER RD. TOTAL FOR
            TUESDAY 07-20-2021. FELL BETWEEN 329 PM AND
            449 PM.

1159 PM     HEAVY RAIN       2 NE DARLINGTON         43.84N 113.38W
07/20/2021  M0.29 INCH       BUTTE              ID   PUBLIC

            W 3900 N. TOTAL FOR TUESDAY 07-20-2021.

1159 PM     HEAVY RAIN       2 SE MACKAY             43.89N 113.59W
07/20/2021  M0.26 INCH       CUSTER             ID   PUBLIC

            PRIVATE WEATHER STATION. TOTAL FOR TUESDAY
            07-20-2021 JUST OFF OF US-93 NEAR SUMMIT DR.

0622 AM     HEAVY RAIN       5 ESE CLEMENTSVILLE     43.86N 111.28W
07/21/2021  M0.25 INCH       TETON              ID   CO-OP OBSERVER

            CO-OP OBSERVER STATION TEXI1. LAST 24 HOURS.

0700 AM     HEAVY RAIN       SODA SPRINGS            42.66N 111.59W
07/21/2021  M0.42 INCH       CARIBOU            ID   COCORAHS

            COCORAHS STATION ID-CR-1. LAST 24 HOURS.
            MULTIPLE SPOTTER REPORTS OF HEAVY RAIN AND
            BRIEF, MINOR FLOODING IN THE SODA SPRINGS
            AREA TUESDAY AFTERNOON FROM THUNDERSTORMS.

0700 AM     HEAVY RAIN       3 NNW LAVA HOT SPRINGS  42.66N 112.02W
07/21/2021  M0.32 INCH       BANNOCK            ID   COCORAHS

            COCORAHS STATION ID-BK-26. LAST 24 HOURS.

0715 AM     HEAVY RAIN       4 W LAVA HOT SPRINGS    42.63N 112.09W
07/21/2021  M0.35 INCH       BANNOCK            ID   CO-OP OBSERVER

            CO-OP OBSERVER STATION TOPI1. LAST 24 HOURS.

0746 AM     HEAVY RAIN       2 NW OVID               42.30N 111.40W
07/21/2021  M0.30 INCH       BEAR LAKE          ID   MESONET

            MESONET STATION EW3600. LAST 24 HOURS.

0946 AM     HEAVY RAIN       3 NE CHESTERFIELD       42.90N 111.83W
07/21/2021  M0.46 INCH       CARIBOU            ID   MESONET

            POLE CANYON RAWS. LAST 24 HOURS.

0950 AM     HEAVY RAIN       14 WSW MACKAY           43.81N 113.85W
07/21/2021  M0.63 INCH       CUSTER             ID   MESONET

            COPPER BASIN RAWS. LAST 24 HOURS.

1003 AM     HEAVY RAIN       CHALLIS                 44.50N 114.22W
07/21/2021  M0.27 INCH       CUSTER             ID   MESONET

            CHALLIS RAWS. LAST 24 HOURS.

&&

KSMITH

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