694
FXUS65 KPIH 181920
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
120 PM MDT Mon Aug 18 2025

.KEY MESSAGES...

- High pressure this week will bring hot and overall very dry
  conditions, with the heat peaking Tuesday and Wednesday.

- Near record to record warmth is expected on Tuesday, with
  highs in the upper 80s to upper 90s.

- Monsoonal moisture building in mid to late week will lead to
  low shower and thunderstorm chances starting Wednesday into
  Thursday increasing and spreading north by the weekend.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 113 PM MDT Mon Aug 18 2025

Early afternoon satellite imagery lending credence to a much
quieter pattern in place than we`ve seen the last several days.
Only a few cu developing over the central Idaho mountains where
isolated showers/thunderstorms are possible this afternoon.
Continued to carry low PoPs in this area to account for a few
weak but gusty shower/thunderstorms through sunset.

Elsewhere clear skies are indicative of the drier air that is in
place and will remain over the next couple of days. High pressure is
building northward into eastern Idaho, allowing mid-summer
temperatures to build back in, challenging a few daily high record
temperatures particularly Tuesday. Nighttime temperatures quite
mild as mid to late August typically brings upper 40s to low
50s for lows, but we`ll be about 10-15 degrees above those
typical readings into Tuesday and Wednesday morning. This will
enhance HeatRisk values to elevated to much of the lower
elevations, especially through the Snake Plain. While this heat
may be impactful to sensitive populations, there appears to be
enough relief overnight to preclude Heat Advisories. Despite the
warmer and drier conditions, fire weather will be slightly less
critical in the near term as winds will be the limiting factor.
Expect breezy conditions, but gusts will generally stay less
than 25 mph each afternoon.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Issued at 113 PM MDT Mon Aug 18 2025

Hot and mainly dry conditions look to persist Wednesday through
Friday under the dominance of upper-level high pressure
centered over the Four Corners. Temperatures remain above
average through this time, with EPS Extreme Forecast Index (EFI)
values highlighting the warmth in both MaxT and MinT fields. A
weak push of monsoon moisture tries to advect north into the
area on Wednesday ahead of a progressive shortwave trough
clipping us as it slides through the Northern Rockies. This
interaction brings back spotty low shower/thunderstorm potential
(less than 20%) to the higher terrain, but not expecting much
from it. Monsoon moisture then looks to remain bottled up across
UT/NV southward Thursday and Friday, leading to continued hot
and dry conditions locally. Beyond that, we continue to see
promising signals among ensemble guidance of a stronger
monsoonal surge over the weekend into early next week. EPS
ensemble mean PWAT values reach 150-175% of normal by Sunday.
This is reflected in NBM precip probabilities as well, with low-
end (20- 30%) shower/thunderstorm chances returning to areas
generally south of the Snake Plain on Saturday, then spreading
north and increasing Sunday and Monday. In the absence of
organized larger-scale forcing, the higher terrain will see the
better rain chances with typical diurnal heating/orographic
forcing, but even the valleys will see at least low precip
chances with the increased moisture in place. Any rain will
certainly be welcome as KPIH hasn`t received measurable
precipitation since July 4th.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1128 AM MDT Mon Aug 18 2025

Strengthening high pressure will bring VFR conditions to all
terminals through the period. Will see some cumulus development
over the terrain this afternoon, but any isolated showers or
thunderstorms are expected to remain north/northeast of all
terminals in the Central Mountains/Montana Divide/Tetons
corridor. Cannot completely rule out a stray afternoon shower
near KDIJ, but chances are less than 10%. Winds will follow a
typical diurnal pattern over the next 24 hours, with gusts
peaking around 20 kts at KPIH and KIDA this afternoon.

&&

.FIRE WEATHER...
Issued at 113 PM MDT Mon Aug 18 2025

High pressure returns to the area, bringing with it warmer and
drier conditions that will persist into midweek and possibly
beyond. Already seeing less area where cumulus development
exists in the afternoon hours, confined mostly to the higher
terrain of the central Idaho mountains. It is here, where some
residual moisture and differential heating could materialize a
few isolated showers and thunderstorms through sunset this
evening. With the isolated nature, RFWs will not be carried for
475/476. Hotter and drier means lower RH values and we`re seeing
that throughout the Snake Plain and terrain into eastern Idaho.
Despite this, winds are expected to remain below the critical
thresholds, keeping RFWs at bay for these locations.

Expect much of the same for Tuesday as temperatures crank up a few
more notches, nearing daily high temperature records for a few
locations through eastern Idaho. RH values will likely drop to 10%
or less for most of central and eastern Idaho, but the limiting
factor will remain the general lack of wind. Breezy conditions in
zones 427 and 476 could lead to some isolated critical fire weather
conditions Tuesday afternoon/evening, but not expected to be
widespread enough to necessitate RFWs at this time.

Wednesday and beyond sees a slight uptick in moisture returning due
to a monsoonal push. This will help knock temperatures back down to
slightly above-normals, creeping RH values up a little bit as well.
Overall, it looks like slam dunk critical fire weather conditions
are not generally expected throughout the week, but we`ll be
threading a needle around near critical in some locations through
the end of the week. Moisture returns in earnest Saturday and Sunday
with monsoonal showers and thunderstorm chances increasing for the
weekend.

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SHORT TERM...TAX
LONG TERM...KB
AVIATION...KB
FIRE WEATHER...TAX