Polaris, Montana Weather Forecast Discussion

392
FXUS65 KTFX 071630
AFDTFX
Area Forecast Discussion
National Weather Service Great Falls MT
Issued by National Weather Service Missoula MT
1030 AM MDT Sun Sep 7 2025
Aviation Section Updated.
.KEY MESSAGES...
- Widely scattered shower and thunderstorm activity develops this
  afternoon and evening, especially over Southwest Montana and
  along The Continental Divide.
- A Pacific weather system then brings more widespread showers
  and thunderstorms Tuesday through Thursday.
- Well above average afternoon temperatures cool closer to the
  seasonal average for the second half of the week.
&&
.UPDATE...
/Issued Issued by National Weather Service Missoula MT/
No major changes were needed with the update this morning. Small
increases to PoPs were made across portions of Central and
Southwest Montana associated with developing light showers,
largely lifting northward. These showers look to diminish late
this morning before a round of afternoon and evening showers and
thunderstorms develops. Given the relatively deep mixing today, a
few of the more robust thunderstorms this afternoon and evening
will be capable of strong wind gusts. -AM
&&
.DISCUSSION...
/Issued Issued by National Weather Service Missoula MT/
- Meteorological Overview:
A passing weather system will bring increased mid- and higher
level cloudiness today. There will also be widely scattered shower
and thunderstorm development, mostly for the western zones. The
primary impact will be localized gusty winds up to 40 mph and
occasional lightning. On Monday shower and storm activity
temporarily retreats to the Northern Rocky Mountain Front before
becoming more widespread around mid-week. Otherwise, expect
mostly warm, dry days with moderate to good humidity recoveries
through early Tuesday.
Current satellite imagery shows mid- and high level cloudiness
increasing from the southwest as monsoon moisture and shortwave
disturbances begin to undercut the ridge aloft. Isolated to widely
scattered shower and thunderstorm activity is expected to develop
later this afternoon into this evening, mostly over the southwest
along the Continental Divide. Localized gusty and erratic winds
and occasional lightning will be the primary impacts given dry
sub-cloud layers with ML CAPE values peaking around 500 to 800
J/kg. This is most concerning over the southwest where conditions
are very dry and there are ongoing wildfires. Despite the
convective activity, warm and dry conditions will prevail for most
areas.
The ridge aloft rebuilds on Monday into early Tuesday for general
warmer and drier conditions before a deepening trough moves onto
the Pacific Northwest coast and brings an unstable southerly flow
aloft over the Northern Rockies. This will usher in an active
weather pattern that will persist for the remainder of the week.
There`s an expectation for periods of scattered to numerous
showers and thunderstorms Tuesday afternoon through Thursday while
temperatures begin to cool closer to average. The combination of
ML CAPE approaching and exceeding 1,000 J/kg, bulk shear around 20
to 30 kts, and precipitable water values rising to the 0.75 to 1
inch range raises concern for at least a few stronger storms
capable of strong, gusty winds, heavy downpours, and hail during
this timeframe.
The precise progression of the Pacific Northwest trough heading
into the weekend remains uncertain. Ensembles have not had run to
run consistency in regards to the path of the system and how
widespread it`s rainfall will be. Overall, periods of showers,
breezy conditions, and near to slightly below average temperatures
can be expected. - RCG
- Forecast Confidence & Scenarios:
Periods of showers and thunderstorms today and next week...
Showers and thunderstorms will have the greatest impact over
central and southwestern locations, south of the highway 12
corridor. HREF thunderstorm wind probabilities continue to
highlight a 50 to 70% chance for gusts over 35 mph. Additionally,
the Storm Prediction Center also has placed much of Beaverhead and
Madison Counties in an isolated dry thunderstorm risk. The
showers and storms will generally move from southwest to northeast
between 3 and 9 pm.
Showers and storms generally retreat to the western mountains on
Monday before returning and becoming more widespread Tuesday
through Thursday. Moisture and instability will be sufficient for
at least a few stronger end storms despite the rapidly lowering
sun angle and shortening days. Thunderstorm related hazards may
include strong, gusty winds, heavy downpours, and hail in addition
to lightning.
Rainfall for the upcoming weekend ultimately depends on the
evolution of the Pacific Northwest trough. It cuts off from the
general circulation, weakens, and undergoes other changes as it
approaches the region, which makes it difficult to narrow down the
precise trek. Periods of showers, some thunderstorms and cooler
temperatures are the most likely scenario, but there`s still
around a 20% chance for some heavy rainfall totals in excess of an
inch for at least portions of the forecast area Friday through
next Sunday. - RCG
&&
.AVIATION...
07/18Z TAF Period
Initial concern this TAF period will be for haze and smoke across
Southwest and portions of Central Montana reducing both surface and
slant-range visiblity. A round of showers and thunderstorms is then
forecast this afternoon and evening, with greatest confidence in
storm coverage across Southwest Montana, mostly after 21Z.
Additional showers and thunderstorms will be much less numerous
further north. Gusty and erratic winds as well as lightning are the
main concerns today from thunderstorms. Smoke continues to press
northeastward through the remainder of the day into tonight, making
it to most plains locations by tonight. -AM
Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF  85  54  82  51 /  20  20  10  10
CTB  83  53  80  48 /  30  20  20  10
HLN  83  53  82  53 /  20  20  10  10
BZN  82  48  81  48 /  30  30   0   0
WYS  72  37  72  37 /  60  30   0   0
DLN  80  45  79  47 /  30  30   0   0
HVR  84  56  82  52 /  10  20  10  10
LWT  82  53  80  51 /  20  20  20  10
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
http://www.weather.gov/greatfalls

NWS TFX Office Area Forecast Discussion