119
FXUS65 KPIH 180745
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
145 AM 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
  increasing shower and thunderstorm chances starting Wednesday
  into Thursday further south, pushing north by the weekend.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 145 AM MDT Mon Aug 18 2025

Early morning satellite imagery shows a series of shortwave
troughs passing over the PacNW and northern Rockies as dry
conditions prevail regionwide across eastern Idaho. Under the
increasing influence of high pressure building north today, the
majority of our area will see hot and dry conditions as isolated
showers and storms are pushed further north. For this
afternoon, best chances for isolated activity will shift north
to being confined up in the eastern Central Mountains and
Montana Divide where the HREF model probability of thunder shows
a 10-20% chance, locally higher in Lemhi County where a 20-40%
chance exists. This region is where HREF probabilities show a
10-30% chance of gusts over 35 mph with storms this afternoon,
locally higher in Lemhi County where a 30-70% chance exists. As
a result, stronger storms (best chances in the eastern Central
Mountains) will remain capable of producing wind gusts up to 45
mph, small hail, and brief heavy rain. Highs today will be
warmer than Sunday by about 3-8 degrees in the mid 80s to low
90s. Synoptic winds outside of any convection will remain light
overall, peaking this afternoon around 10-20 mph with gusts to
20-30 mph.

As the ridge axis of a broad region of high pressure becomes
centered over the Four Corners region north into Wyoming and
Montana on Tuesday, temperatures here in eastern Idaho will
climb another 4-6 degrees with highs reaching the upper 80s to
upper 90s. This level of warmth is about 8-14 degrees above
normal for this time of year, supporting near record to record
warmth with our latest forecast highs on Tuesday. As a result,
Tuesday is shaping up to be one of the warmest days so far this
year, with a 10-20% chance of reaching the 100s across our
lowest elevations. Conditions will also remain very across the
board, with afternoon RHs mostly in the single digits, with
perhaps some isolated showers and virga up in Lemhi County.
Afternoon winds will remain in similar to shape to Monday,
peaking around 10-20 mph with gusts to 20-30 mph.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Issued at 145 AM MDT Mon Aug 18 2025

Under the continued influence of high pressure mid to late
week, conditions overall will remain hot and dry as increasing
confidence supports monsoon moisture rotating around a Four
Corners high progressing north up into the northern Great Basin
and Rockies later in the week. While chances are still looking
isolated through the work week, staying mostly southeast of the
Snake River Plain, those chances will steadily increase for the
weekend into early next week with an expansion to regionwide
isolated to scattered coverage expected. Increased moisture and
cloud cover moving in will lead to cooler temperatures for
Sunday and Monday, with highs cooling from the mid 80s to mid
90s Wednesday through Saturday to the upper 70s to upper 80s by
Monday.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 941 PM MDT Sun Aug 17 2025

Convection is over for all TAF sites for this evening. There
are lingering isolated showers and thunderstorms in the Island
Park area but will be out of Southeast Idaho in the next hour.

High pressure builds in tonight into tomorrow bringing overall
clear skies and lighter winds. Winds will gust to around 20 kts
for IDA, PIH and DIJ tomorrow afternoon. Expect light winds and
clear skies by early tomorrow evening.

&&

.FIRE WEATHER...
Issued at 145 AM MDT Mon Aug 18 2025

Under the increasing influence of high pressure building in out
of the south today, hot and dry conditions are expected across
much of the region as isolated showers and thunderstorms shift
north to being confined to the Central Mountains east along the
Montana Divide. Dry conditions will return regionwide for
Tuesday as highs climb into the upper 80s to upper 90s in the
valleys with afternoon RHs mostly in the single digits given a
very dry airmass in place. As a result, Tuesday is shaping up to
be the hottest day of the week with near record to record
warmth expected. We may ultimately see some isolated showers and
virga up in Lemhi County for Tuesday afternoon, but conditions
will remain hot and very dry overall.

Above normal temperatures with highs in the mid 80s to mid 90s
will then continue for Wednesday through the rest of the week
with afternoon RHs mostly in the single digits and teens. Winds
this week look to remain light, but they will see a diurnal
increase each afternoon with gusts peaking around 20-30 mph. At
this time, we are not expecting widespread critical fire weather
conditions due to a combination of wind and low RH, but we may
see pockets of near critical to critical conditions at times.

While conditions overall will remain hot and dry through the
remainder of the week, increasing confidence supports monsoon
moisture rotating around a Four Corners high progressing north
up into the northern Great Basin and Rockies later in the week.
While chances are still looking isolated through the work week,
staying mostly southeast of the Snake River Plain, those chances
will steadily increase for the weekend into early next week
with an expansion to regionwide isolated to scattered coverage
expected. Increased moisture and cloud cover moving in will lead
to cooler temperatures and increased RHs during this timeframe,
with highs cooling from the mid 80s to mid 90s Wednesday
through Saturday to the upper 70s to upper 80s by Monday as
afternoon RHs climb into the 20s/30s starting Sunday.

&&

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

&&

$$

SHORT TERM...MacKay
LONG TERM...MacKay
AVIATION...TW
FIRE WEATHER...MacKay