098
FXUS65 KTFX 140433
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1033 PM MDT Sat Sep 13 2025

Aviation Section Updated.

.KEY MESSAGES...

 - Near to above normal temperatures to continue for much of the
   next week.

 - Daily chances for showers and thunderstorms through the first
   half of the upcoming work week.

&&

.UPDATE...

/Issued 539 PM MDT Sat Sep 13 2025/
Current forecast is on track, with scattered showers and isolated
thunderstorms affecting the CWA. Most of the precipitation will
diminish by Midnight. Brusda


&&

.DISCUSSION...
/Issued 539 PM MDT Sat Sep 13 2025/

 - Meteorological Overview:

Longwave troughing, with embedded waves sliding east/lifting
northeast from the Pacific Northwest/Great Basin and over the
Northern Rockies, will remain over the Western CONUS through the
first half of the upcoming work week before transient upper level
ridging over the Eastern Pacific amplifies and builds east on
Wednesday. This longwave troughing pattern will help to maintain
daily chances for showers and thunderstorms across Southwest through
North Central Montana through the first half of the upcoming work
week, with temperatures running near to above normal. Shower and
thunderstorm coverage today and tonight will be greatest along and
east of a Bozeman to Havre line, but even isolated showers and
storms will be possible west of this line and up to the Continental
Divide. While severe thunderstorms are not expected through this
timeframe given weak shear, sufficient instability and PWATs will
support the potential for gusty/erratic winds and brief periods of
heavy rainfall beneath the strongest storms. Sunday will largely see
dry conditions through the morning and early afternoon hours as the
Northern Rockies resides between embedded wave, with increasing
coverage of showers and thunderstorms thereafter into the evening
and overnight hours as the next embedded wave pivots over the
region. Shower and thunderstorms chances will continue through the
day on Monday, with a weak cold fronts pushing south and across
Montana during the afternoon and evening hours. This cold front will
help to bring the "coolest" conditions of the unsettled pattern,
with temperatures rebounding on Wednesday as the aforementioned
upper level ridge builds eastward and over the Northern Rockies.

After a brief period of transient ridging on Wednesday a potent
shortwave over the Gulf of Alaska/Eastern Pacific will begin to lift
northeastward and over Western Canada and the Pacific Northwest.
This lifting shortwave will help to flatten the ridge over the
Northern Rockies through the remainder of the work week, with quasi-
zonal developing over Southwest through North Central Montana from
Thursday/Friday and persisting into next weekend. Near to slightly
above normal temperatures will continue beneath this quasi-zonal
pattern, with additional chances for precipitation occurring across
most locations. - Moldan

 - Forecast Confidence & Scenarios:

Heavy Rainfall Today/Tonight :

Latest HREF (Hi-Res Ensemble Forecast) guidance supports a 10%
chance for hourly rainfall rates to reach or exceed 0.25" across
mainly Blaine and Fergus Counties from the late morning through
afternoon hours, with 90th Percentile 24hr rainfall accumulations of
0.5" to 1" over the Island ranges of these two counties. While an
isolated storm or two producing brief periods of heavy rainfall
leading to ponding of water in low-lying or poor drainage areas
(i.e. urban locations like Lewistown) can`t be ruled out...the
overall threat for heavy rainfall leading to flooding is quite low
given the available probabilistic data. - Moldan

&&

.AVIATION...

VFR conditions will prevail throughout the 1406/1506 TAF period,
but scattered to broken mid-level cloudiness will persist over the
next 24 hours. An approaching disturbance will bring increasing
precipitation chances to areas along the Continental Divide and
across Southwest Montana beyond 00z Monday. Widespread mountain
obscuration is not expected through 00z Monday, but increasing
obscuration is expected thereafter. - Moldan

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  50  81  54  70 /  10   0  20  40
CTB  47  79  52  68 /  10  10  10  40
HLN  50  80  52  67 /  20  10  40  50
BZN  44  79  46  64 /  10  10  30  50
WYS  32  67  35  55 /  20  10  20  60
DLN  42  74  43  61 /  10  10  40  40
HVR  50  81  52  76 /   0   0  10  20
LWT  48  78  49  68 /  20  10  10  40

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$
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