350
FXUS65 KPIH 211955
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
155 PM MDT Tue Jul 21 2026

.KEY MESSAGES...

- Flash Flood Risk & Active Flood Watches: Deep monsoonal
  moisture carrying Precipitable Water (PWAT) values near the
  99th percentile has prompted a Flood Watch for the Eastern and
  Southeastern Highlands, as well as the Wapiti Burn Scar in
  the Central Mountains. Slow-moving thunderstorms through
  Wednesday will be capable of torrential rainfall, localized
  flash flooding, and debris flows on recent burn scars.
  Secondary storm hazards include gusty outflow winds and small
  hail.

- Peak Moisture Window Today & Wednesday: This 2436 hour
  stretch represents the wettest period of the 7-day forecast.
  Extensive cloud cover will keep daytime highs limited to the
  80s in lower elevations and mid-to-upper 70s in the mountains.

- Late-Week Pattern Shift & Returning Heat: A drying and
  warming trend begins Thursday. High temperatures will climb
  back into the mid-90s across lower valleys this weekend and
  into early next week.

&&

.DISCUSSION...
Issued at 147 PM MDT Tue Jul 21 2026

A robust plume of monsoonal moisture continues to surge into
eastern Idaho this afternoon, setting the stage for an active 24
to 36 hours across the region. Isolated to scattered showers
and thunderstorms will continue to develop through the remainder
of the afternoon and persist into the early overnight hours.
While a brief lull in convective coverage is possible early
Wednesday morning, a secondary, potent wave of deep atmospheric
moisture will stream into the area shortly thereafter.

Precipitable Water (PWAT) values on Wednesday will climb well
above climatological norms, approaching the 99th percentile for
late July. This atmospheric profile will yield exceptionally
efficient, heavy-rainfall-producing showers and thunderstorms.
Given the slow movement of these storms and high rain rates,
localized flash flooding is a major concern. Consequently, a
Flood Watch has been issued for the Eastern and Southeastern
Highlands, as well as the Wapiti Burn Scar across the central
mountains where debris flows will be a heightened risk. While
the watch area currently encompasses the highest confidence for
heavy rain, areas outside the watch across eastern Idaho remain
vulnerable to localized flash flooding if slow-moving cores
track directly overhead. Widespread cloud cover and
precipitation will limit diurnal heating, capping Wednesday
highs in the 80s for lower elevations and the mid-to-upper 70s
across higher terrain. Gusty outflow winds and small hail will
also accompany stronger cells.

Wednesday into Wednesday night will mark the wettest phase of
the 7-day period. Beginning Thursday, the main monsoonal
moisture axis will end, initiating a transition back to a warmer
and drier pattern heading into the weekend and early next week.
While lingering mid-level moisture will maintain low-end daily
shower and thunderstorm chances over the higher terrain, overall
convective coverage will be isolated. Heat will quickly re-
emerge as the primary operational impact, with high pressure
building back over the Intermountain West to push lower-
elevation afternoon highs back into the mid-90s as early as
Friday and continuing into early next week and likely much
longer.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1126 AM MDT Tue Jul 21 2026

A few showers linger late this morning/early this afternoon, but
we are seeing a short break in the monsoon moisture at the
moment. That is expected to change later this afternoon as
thunderstorms begin to pop up once again. PROB30 remains in the
TAF at all sites, but for many, storms will arrive after 00Z
this evening, so may only produce gusty winds for a short period
before they begin to fizzle into more showery activity.
However, any stronger storm that does get going, could produce
strong gusts around 40kts. Showers and storms increase in
coverage tomorrow and storms on Wednesday aren`t expected to
produce as strong of wind gusts since they will produce more
rain, so expect another round of PROB30 in the TAFs at next
issuance.

&&

.FIRE WEATHER...
Issued at 147 PM MDT Tue Jul 21 2026

Monsoon moisture continues to bring isolated to nearly scattered
showers and thunderstorms to portions of Fire Weather Zones 413,
northern 422, 427, 475, and 476 this afternoon. Coverage actually
begins to increase later this evening, after 1800 MDT. Stronger
storms today will be capable of producing strong wind gusts of 40 to
50 mph and will be a mix of wet and dry storms.

Moisture content increases in a big way on Wednesday with PWATs
ranging from almost 1.00 to 1.50 inches across all of our coverage
area, much higher than normal for this time of the year. With the
better chance for any storm to produce a wetting rain, the wind
threat diminishes for Wednesday with gusts more likely around 35-45
mph. Given how wet these storms will be, we have opted to NOT issue
a Red Flag Warning even though we will reach "scattered"
thunderstorm criteria at almost every Fire Weather Zone on
Wednesday. So, expect showers and thunderstorms producing lightning,
but also producing a wetting rain. We will be watching the Wapiti
burn scar for flash flooding potential as well as watching the Ohio
fire area for any flash flooding there, too.

On Thursday, isolated thunderstorms will linger in the Central
Mountains and Eastern Highlands, and while we won`t completely shut
off our monsoons moisture for Friday and the weekend, it will be
much drier overall. Winds begin to increase on Friday and Saturday
afternoons with gusts of 25 to 35 mph and afternoon min RHs falling
into the teens and 20s.


&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Flood Watch from Wednesday afternoon through Wednesday evening
for IDZ058>066.

&&

$$

DISCUSSION...McKaughan
AVIATION...AMM
FIRE WEATHER...AMM