819
FXUS65 KTFX 090530
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1130 PM MDT Mon Sep 8 2025

...Aviation Section Updated...

.KEY MESSAGES...

 - Showers and a few thunderstorms this afternoon, primarily
   across North-central Montana.

 - Thunderstorms increase in coverage for the Tuesday through
   Thursday timeframe, largely in the afternoon and evening. A few
   of these thunderstorms will be on the stronger side.

 - Confidence in specifics remains low for the Friday into
   early next week timeframe, but periods of rain and cooler
   temperatures are favored.

&&

.UPDATE...

Widely scattered showers and a few isolated/weak thunderstorms
that formed across primarily north-central MT this afternoon will
dissipate rather quickly through the rest of this evening as low
level instability/CAPE diminishes. Remnant clouds are also likely to
decrease through the overnight period with general upper level
ridging remaining in place across the region. Hoenisch

&&

.DISCUSSION...
/Issued Issued by National Weather Service Missoula MT/

 - Meteorological Overview:

A potent trough off the Pacific Northwest coastline will continue
to nudge eastward over the next 24 hours or so before becoming
essentially stationary across the interior Pacific Northwest from
Tuesday through Thursday. This will result in a long duration
southerly to southwesterly flow aloft, which in combination with
forcing from the troughing and any related ejecting waves moving
across the Northern Rockies, will result in several days worth of
primarily afternoon and evening showers and thunderstorms.

Before the troughing becomes entrenched tomorrow, the
southwesterly flow aloft today will feature a bit of shortwave
ridging across the region, which will help limit overall coverage
of showers and thunderstorms. Areas most favored to see a shower
or thunderstorm today are across North-central Montana and into
portions of Central Montana, though the probability is rather low
(Say 20% or so for any given location). Forecast soundings do not
show much in way of instability, and shear also appears to be
quite low, hence any thunderstorm that forms should be brief and
on the weaker side.

Heading into Tuesday through Thursday the potential for showers
and thunderstorms increases again. Magnitude of instability
increases each day, peaking for most areas on Thursday. Shear also
trends higher into Thursday, yielding an increased risk for
strong thunderstorms for Wednesday and especially Thursday.
Specifics such as when and where for these stronger thunderstorms
remains lower in confidence.

Looking toward Friday and into early next week, there still
remains quite a bit of spread between potential outcomes. Upper
troughing that will be nearly stationary over the interior Pacific
Northwest will slowly move over the Northern Rockies Friday into
the weekend, becoming nearly stationary once again. Embedded waves
within this troughing, in add addition to additional troughing
moving in across the Pacific Northwest from the eastern Pacific
Ocean later this weekend looks to result in periods of rain across
the region, with temperatures trending close to, if not a touch
below average for some areas. This timeframe does not look like a
washout, but picking out which timeframes will be dry vs wet is
very low confidence at this range. -AM


 - Forecast Confidence & Scenarios:

The main source of uncertainty continues to be Friday through
early next week. Over the 72 hour period ending 6 AM Monday, the
spread between 10th percentile (Reasonable low-end scenario) and
90th percentile (Reasonable high-end scenario) precipitation is
greater than an inch across the entire forecast area. Some areas
across the plains east of I-15 have a greater than 3 inch spread
between potential outcomes. EX: In the Snowies the reasonable low-
end precipitation amount over the aforementioned timeframe is
~0.25. Meanwhile the reasonable high-end precipitation amount is
~ 3.75. The overall pattern is quite complex, and may take longer
than normal before confidence in precipitation amounts increases.
-AM

&&

.AVIATION...
09/06Z TAF Period

Mostly clear skies are expected overnight and the morning. Cloud
cover increases ahead of afternoon and evening showers and
thunderstorms. There is a little uncertainty in the timing of
thunderstorms Tuesday as there may be a few waves of precipitation.
The main concern with a few thunderstorms will be stronger wind
gusts. Wildfire smoke and haze lingers into Tuesday, but surface
visibilities are expected to stay above VFR conditions. -Wilson

Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  50  84  53  82 /  20  30  40  10
CTB  46  81  50  78 /  20  20  30  30
HLN  52  82  53  82 /  10  40  40  20
BZN  46  81  48  81 /   0  40  30  20
WYS  36  70  38  71 /   0  50  40  30
DLN  45  73  45  77 /   0  30  30  20
HVR  51  85  56  84 /  10  10  20  20
LWT  50  82  52  82 /  20  10  30  20

&&

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

$$
http://www.weather.gov/greatfalls