971
FXUS65 KPIH 122004
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
204 PM MDT Wed Aug 12 2026

.KEY MESSAGES...

- Isolated to scattered thunderstorms this afternoon. Gusty
  outflow winds possible near storms.

- Threat for showers and thunderstorms increases Thursday
  through Saturday.

- Locally heavy rain possible with burn scars most vulnerable.

&&

.DISCUSSION...
Issued at 154 AM MDT Wed Aug 12 2026

Expect a mix of wet and dry storms today with strong gusty
outflow winds possible near storms today. Most of the activity
should diminish tonight.

On Thursday, a low pressure system will eject out of California and
advance towards south Idaho. Models are showing a band of showers
with isolated to scattered thunderstorms within and around this band
of showers. This is expected to arrive Thursday afternoon with
models showing quite a bit of moisture across the eastern highlands
as this feature moves north. Potentially this could bring 0.25 to
0.50 inches of rain just Thursday afternoon. Confidence is moderate
to high of appreciable rain on the Big Rock fire east of Idaho
Falls. So have decided to issue a flood watch for the burn. While
other burn scars may need watches as well with this feature moving
north, this particular burn scar is the most likely to see heavy
rain assuming the track of the low doesn`t shift appreciably.

As we move into Friday, a secondary weaker trough will arrive from
the southwest and provide the trigger for additional convection. The
models seem to be favoring the central mountains into the upper
Snake River highlands for appreciable rainfall with over 0.10 inches
forecast Friday afternoon. So we may need additional flood watches
for burn scars and possibly for the Big Rock again. On Saturday, one
additional shortwave trough will move through the region resulting
in scattered showers and thunderstorms with the main focus once
again across the central mountains into the Island Park region. With
the monsoon air firmly in place, the threat for flash flooding on
these burn scars will likely continue. As we head into Sunday and
Monday, a ridge retrogrades from the east and and builds across the
area. This will shut down the "organized" thunderstorms. But the
monsoon moisture will remain in place. So we`ll probably keep
continued chances for isolated storms into early next week. The
forecast at this point could very well be too dry on pops with the
models assuming too strong of a cap in place.

From a temperature perspective, today is the last warm day with
cloud cover and showers providing cooler temperatures into the
weekend. As we head into next week, temperatures rebound into the
80s but not the extreme heat that we`ve been experiencing.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1003 AM MDT Wed Aug 12 2026

Main concern today still involves isolated to scattered
thunderstorms this afternoon. Looking at 30% chance of storms on
station and/or moderate to strong (around 40 knots) outflow
winds affecting the terminal at most locations. HREF model shows
PIH and DIJ the most likely to have thunderstorms on station
this afternoon. SUN is probably the only location that models
keep storms away from this afternoon. Showers and thunderstorms
move out of the area by early evening.

The next big round of showers and thunderstorms is expected
Thursday. Have added VCSH for BYI at 12Z and VCSH for PIH, IDA
and SUN by late tomorrow morning. Have added a PROB30 for TSTMs
for BYI by late tomorrow morning and a PROB30 for TSTMs for SUN
by mid tomorrow afternoon. Confidence for thunderstorms is
gaining. So, will likely move TSTM to the predominant weather
for BYI and SUN (and other TAF sites) as we get closer.

&&

.FIRE WEATHER...
Issued at 200 PM MDT Wed Aug 12 2026

A trough situated along the PacNW coast will support decreasing
temperatures under increasing cloud cover, as well as the return of
monsoon moisture and daily showers and thunderstorms. Daytime highs
are warming to just below normal today before turning cooler than
normal for the remainder of the week. Isolated storms this afternoon
will primarily impact the southeast highlands and MT Divide region.
The main monsoon surge will arrive tomorrow and continue through
Saturday. This will raise humidities and provide much-needed rain
but also introduce frequent lightning. While thunderstorms will
trend wetter heading into Friday and Saturday, a mix of wet and dry
thunderstorms is anticipated Thursday. Thus, RED FLAG WARNINGS have
been issued for ID Fire Weather Zones 410, 411, 413, 422, 425, 427,
475, and 476 on Thursday due to scattered thunderstorm coverage and
the potential for new fire starts due to lightning. Storms over the
next few days will be capable of producing gusty erratic winds up to
45 mph and locally moderate to heavy rain, which could lead to
localized flooding over burn scars. Of particular concern is the Big
Rock fire, which is forecast to receive approximately half an inch
of rain over 48 hours Thursday and Friday, although rain
accumulation will be highly dependent on whether or not storms pass
directly over the fire and burn scar or not.

&&

.HYDROLOGY...
Issued at 1028 AM MDT Wed Aug 12 2026

Monsoon moisture moves into our area from the south and will
increase rainfall amounts and rates, especially Thursday and
Friday. Any thunderstorms that develop are expected to be
efficient rain producers with rain rates approaching 1 inch per
hour. Most flooding concerns will be with recent burn scars. A
flash flood watch is currently in effect for the Big Rock burn
scar east of Idaho Falls for Thursday afternoon into the early
evening. Flash flood watches will likely be needed on Friday for
the Ohio fire burn scar south of Ketchum and the Wapiti fire
burn scar north and west of Stanley. Outside of burn scars,
localized flooding is less likely but possible, especially for
any slow moving or repetitive thunderstorms.

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon to 9 PM MDT Thursday for IDZ410-411-
413-422-425-427-475-476.

&&

$$

DISCUSSION...13
AVIATION...TW
FIRE WEATHER...Cropp
HYDROLOGY...TW