Thornton, Idaho Weather Forecast Discussion

457
FXUS65 KPIH 272355
AFDPIH
Area Forecast Discussion
National Weather Service Pocatello ID
555 PM MDT Sat Sep 27 2025
.KEY MESSAGES...
- A few locations will reach 80 degrees today and Sunday, but
  temperatures turn much cooler for the upcoming week.
- Showers and thunderstorms develop Sunday afternoon in the
  south, spread northward Monday morning and continue through at
  least Tuesday.
- Next frontal system may arrive by next weekend.
&&
.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 131 PM MDT Sat Sep 27 2025
Hardly a single blip on the satellite imagery across East Idaho
early this afternoon. High pressure keeps skies clear through
the evening, then some moisture begins to creep into the
southern portions of the forecast area overnight ahead of
opening upper low across the southwest begins to shift
northeast. Sunday sees shower and thunderstorm potential
increase across the south and east, but can`t completely rule
out some isolated development over the central mountains either
as we see some growing support for that in the high-res models
today. Temperatures start to moderate Sunday by a few degrees,
though Magic Valley and Raft River areas could still see
temperatures reach the lower 80s. Would not be surprised to see
a few showers linger after midnight Sunday night, though most of
the activity should dissipate during the evening.
&&
.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 131 PM MDT Sat Sep 27 2025
Moving into the work week, models remain confident in pushing a
shortwave out of the base of the deep Pacific trough inland Monday,
ejecting it across Idaho Tuesday. Most of the precipitation appears
to be holding to the west for Monday, though isolated to scattered
showers and thunderstorms remain possible Monday afternoon across
the Snake Plain and eastern highlands as well. Precipitation band
works across the region Monday night into Tuesday, for the best
chances of rainfall region-wide. The late Monday time frame may be
the period of most concern for burn scar impacts across the central
mountains, and heavier rainfall potential from embedded
thunderstorms may be a concern to keep in mind for the next couple
forecast cycles. Temperatures cool Monday and Tuesday behind the
warmth from this weekend, with daytime highs by Tuesday in the mid
60s to lower 70s. Moving into the latter half of the week, ensemble
clusters have split with nearly half retaining a closed low centered
off the Seattle/Vancouver coast while the rest open the low and
begin to weaken the trough. Flow remains southwest across Idaho with
some moisture still available to maintain precipitation chances. NBM
blend keeps isolated to widely scattered showers across higher
elevations, drying most of the region out into Thursday but keeping
higher chances across the central mountains closer to the trough
feature. Next shortwave ejects out of the trough and across East
Idaho for the Friday/Saturday time frame, with renewed precipitation
chances most areas associated with a stronger frontal passage.
Timing of the front could have some implications for wind potential
late in the week, but that would be tough to nail down this far
out.
&&
.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 555 PM MDT Sat Sep 27 2025
Mostly clear skies and very low-impact conditions for aviation
continue this afternoon! Clouds are forecast to gradually
increase from south to north overnight tonight, with most
terminals VFR but BKN by 11-13z/5-7am Sunday...courtesy of a
low pressure system to our south over the Four Corners region.
Have massaged timing and increased detail in the TAFs for this
push of moisture based on the latest NBM and HREF trends. KSUN
will reside in the northwest fringes of the cloud cover and may
be able to hold SCT. Some of the high-res CAMs do develop
isolated light shower activity Sunday morning, but confidence is
very low on occurrence, coverage, and placement, thus will not
add VCSH to any of the TAF sites with the 00z forecast package.
By Sunday afternoon, moisture continues to trend higher with a
general increase in diurnal convective development noted across
the suite of CAMs (supported by NBM PoP trends as well)...it`s
just enough that we`ve introduced PROB30 groups for -TSRA
everywhere but KSUN starting between 19-21z/1-3pm. Looking at
model forecast soundings, traditional instability/CAPE as well
as DCAPE are marginal (and DCAPE less than 1,000 J/kg is
accompanied by PWATs increasing above 0.8 inches and pretty
modest resultant HREF ensemble max wind gusts), suggesting
thunderstorms should stay fairly weak with not much wind
potential (possible gusts only to 25kts). With sfc winds
otherwise generally holding 10kts or less and cigs remaining
VFR, and modest winds aloft as well, this thunderstorm
potential will be the main aviation threat to watch for the
afternoon and early evening. In future updates we should be able
to shut down shower/t-storm potential around sunset Sunday
evening leading to a quiet night, but more precipitation is on
the way for Monday and Tuesday as a shortwave trough pushes
through from the west.
&&
.FIRE WEATHER...
Issued at 131 PM MDT Sat Sep 27 2025
Will start to see a bit of a pattern change with a return to a
chance of showers Sunday night and continuing with a chance daily
through next weekend. Will see above normal temperatures
continuing through Thursday then a significant cool down Friday
into next weekend. Wettest days likely Tuesday and then next
Friday and Saturday. Very high elevations could see snow next
Friday and Saturday, but low probabilities that far out.
Windiest days also likely next Friday and Saturday behind strong
cold frontal passage.
&&
.PIH WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...DMH
LONG TERM...DMH
AVIATION...KSmith
FIRE WEATHER...GK

NWS PIH Office Area Forecast Discussion