423
FXUS65 KPIH 092302
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
502 PM MDT Fri Oct 9 2026

.KEY MESSAGES...

- Flood Watch In Effect (SaturdayMonday): A Flood Watch covers
  most of eastern Idahoincluding Sun Valley east through the
  Magic Valley, Snake Plain, and Eastern/Southeastern
  Highlandsfor a multi-day rainfall event of 1.0 to 2.0 inches,
  with localized totals up to 3.0 inches possible near Island
  Park and into the eastern Highlands. NBM guidance shows an 80%
  to 100% probability of exceeding 1.0 inch of rainfall
  along/east of the I-15 corridor and the South Hills, with a
  30% to 80% probability of exceeding 2.0 inches.

- Dramatic Weekend Cooldown: Today`s upper 70s and 80s mark the
  final warm day of the season. Highs drop below 70 on Saturday
  and plummet into the 40s and 50s on Sunday.

- Frost/Freeze Headlines Ahead: Widespread cool temperatures
  will bring frost/freeze risks starting Sunday morning,
  becoming more likely Monday through mid-week before headlines
  are suspended for the season.

&&

.DISCUSSION...
Issued at 206 PM MDT Fri Oct 9 2026

A major pattern shift gets underway across the Intermountain
West today. Satellite imagery shows increasing cloudiness over
eastern Washington and Oregon associated with an approaching
upper-level trough. Temperatures today have climbed quickly into
the 70s and 80s, marking the final day of 80-degree warmth for
the foreseeable future. Saturday represents the leading edge of
the cooler, wetter air mass, with lower-elevation maximum
temperatures struggling to reach 70 degrees. Showers and
embedded thunderstorms will develop during the day on Saturday,
elevating localized rainfall rates and initiating a multi-day
precipitation event.

Sunday will be the wettest and most impactful day of the
forecast period as the upper-level low tracks slowly across the
Great Basin. A Flood Watch has been issued for most of eastern
Idaho, extending from Sun Valley eastward across the Magic
Valley, Snake Plain, and the Eastern and Southeastern Highlands.
Widespread rainfall totals of 1.0 to 2.0 inches are very likely
between Saturday and Monday. National Blend of Models (NBM)
probabilities for storm totals exceeding 1.0 inch reach 80% to
100% along and east of the I-15 corridor and into the South
Hills, with 2.0-inch probabilities ranging from 30% to 80%. The
highest QPF footprint is focused across the Eastern Highlands
and toward Island Park, where localized 3.0-inch totals are
possible. While persistent light-to-moderate rain is the primary
driver, embedded Saturday/Sunday convection could boost
localized totals and create localized flooding concerns. Strong
cold advection on Sunday will hold daytime highs in the 40s and
50s.

As the primary upper low slowly crosses the Intermountain West,
precipitation chances will linger through Monday and Tuesday.
Rainfall intensity will wane compared to Sunday, with conditions
gradually drying out by mid-week. Unseasonably cool air will
remain locked over the region, holding daytime highs in the 50s
through much of next week, with a slight recovery toward the
lower 60s possible by late week. With cold air established
behind the departing system, attention shifts to overnight
freeze risks. Frost and freeze headlines may be needed as early
as Sunday morning, with a much higher likelihood Monday morning
through mid-week as skies clear during overnight hours. These
chilly nights will likely result in the seasonal suspension of
Frost/Freeze headlines for eastern Idaho at some point mid-week.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 457 PM MDT Fri Oct 9 2026

Conditions are certainly changing this evening/tonight as a cold
front moves into the area and quite a bit of moisture takes aim
at Eastern Idaho for the weekend. There are a few showers out
there already this evening, so added some VCSH at DIJ. Showers
look more likely to remain south of BYI, PIH, IDA, and SUN for
the rest of this evening. Look for a quick round of showers
early Saturday before a brief break ahead of isolated to
scattered showers and storms Saturday afternoon. The intensity
of thunderstorms on Saturday afternoon remains questionable as
temperatures will be dropping by that point. We remain breezy
this evening with gusts around 20-25 kts, but will diminish
briefly overnight before picking up to 20-25kts again on
Saturday. SUN looks to stay the driest on Saturday, but should
join in on the action by late Saturday night or early Sunday
morning. At this point, mostly VFR conditions will continue, but
that becomes less likely as clouds lower and rainfall increases
Saturday night into Sunday.

&&

.FIRE WEATHER...
Issued at 206 PM MDT Fri Oct 9 2026

Fall arrives this weekend across East Idaho. Winds remain gusty
this afternoon, with critical or near critical conditions
especially across the southwest amid very dry humidities.A Red
Flag Warning remains in effect until 8 pm for Zone 427. Winds
remain breezy overnight, but humidities rise after sunset.
Moisture continues to increase overnight as remnants of tropical
system Rachel begin to push through the Great Basin ahead of
upper low dropping through the Pacific Northwest. The
combination of these features will result in a rapid change in
the pattern through the weekend, with onset of isolated to
widely scattered showers arriving as early as tonight across the
central mountains, spreading across the remainder of East Idaho
through the day Saturday. Rainfall continues into early next
week, but Sunday looks to be the heaviest day for most areas.
Overall totals Saturday through Monday are forecast to range
0.35-0.50" for zones 475 and 476, 0.50-1.50" for much of the
Snake Plain. More widespread totals for the 3 day period are
across the southern and eastern highlands, zones 427, 413, and
411, where some locations will exceed 2" of liquid
precipitation. A Flood Watch is now in effect Saturday afternoon
through Monday for regions expected to see the highest rainfall
totals. Much cooler temperatures drop into East Idaho along with
the rainfall, which means accumulation of snow at higher
elevations, briefly dipping to mid-slopes especially across the
central mountains during overnight hours. The greatest affects
will be above 7500-8000 ft elevations.

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Flood Watch from Saturday afternoon through Monday afternoon
for IDZ051>067-073-075.
Red Flag Warning until 8 PM MDT this evening for IDZ427.

&&

$$

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