753
FXUS65 KTFX 061749
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1149 AM MDT Sun Sep 6 2026

Aviation Section Updated.

.KEY MESSAGES...

 - Thunderstorms, some strong to severe, are expected to move
   through Montana this evening, particularly north of a Helena
   to Lewistown line.

 - Widespread soaking rainfall expected tonight through Tuesday
   morning, with widespread rainfall amounts over an inch across
   the plains, with lighter amounts across Southwestern Montana.

 - Drier conditions return Wednesday, but precipitation returns
   Thursday night into Friday.

&&

.DISCUSSION...
/Issued 300 AM MDT Sun Sep 6 2026/

Deep upper level troughing located over Washington and Oregon
will continue slowly drift eastward over the coming days, which
will bring a prolonged period of unsettled weather to the Treasure
State. Overnight radar has continued to show some showers and
thunderstorms drifting from SW to NE in two areas: the first
stretching from around Missoula to Cut Bank, and the second along
and east of a line from Lewistown to Havre. These two areas will
likely continue to persist through late this morning, before a
break arrives for early afternoon. A second, stronger round of
showers and thunderstorms will push through the area, with some of
the storms becoming strong to severe (more on this below).

Another round of precipitation will arrive on Monday as a mix of
convective and stratiform precipitation, which will generally hang
across the plains through Monday night and into Tuesday morning.
The convective elements within this precipitation will result in
some rather impressive rainfall totals, with most areas across the
plains likely to see at least 1 to 2 inches through early
Tuesday, with isolated to scattered amounts in excess of 3 or 4
inches along and west of Interstate 15 possible where some of the
heavier convection repeatedly moves over the same areas. While
flooding is not expected to be a major concern given the overall
gradual nature of the rainfall, some field/poor drainage flooding
cannot be ruled out.

Weak upper level ridging will return to the area Wednesday and
Thursday, bringing a reprieve from the rainfall for a brief
period, but another, albeit weaker and faster moving, trough will
swing through Friday and Saturday, bringing another round of
widespread rainfall.

 - Forecast Confidence & Scenarios:

Thunderstorms today: A potent vort max embedded within the upper
level flow will push into Southwestern Montana late this
afternoon, kicking off a few showers and thunderstorms as it does
so. As these storms reach the plains, they will encounter one of
two environments: The first is a heavily capped environment,
albeit one with still enough shear to allow the storms to remain
organized and produce some hail as they move northeastward. The
second possibility is that these storms will encounter a weakly
capped atmosphere, which would allow the storms to tap into
stronger shear and have the potential to become surfaced based,
allowing both wind and hail to reach the ground as the storms
evolve into supercells. The Storm Prediction Center has placed
most of the area in a slight risk for severe thunderstorms,
primarily due to the threat of large hail.

Heavy rainfall through Tuesday: Heavy rainfall through Tuesday
will result in a widespread 1 to 2 inches of rainfall across the
plains, with around a 10% chance of seeing over 4 inches along and
west of Interstate 15 north of Great Falls. So far, soils in this
area seem to have readily accepted the copious amounts of
rainfall, as areas along the Rocky Mountain Front that have
received over an inch of rainfall over the past 24-36 hours have
not really seen rivers respond in any meaningful way. This gives
hope that soils will continue to be receptive to precipitation,
though as soils continue to absorb rainfall it is possible that
the soils will saturate and result in some field and poor drainage
areas, along with some rises on rivers and streams. A Flood Watch
was considered, and may still be considered in future updates, but
for now soils appear to be capable of handling this long duration
rainfall event.

&&

.AVIATION...
06/18Z TAF Period

Low clouds/light precip will affect portions of North Central MT
early this afternoon. Then a wave of strong storms will move from
southwest to Northeast through the Central and North Central MT
this evening and overnight. Expect strong winds and some hail with
this wave. The stronger storms transition to more of a stratiform
rain by Monday morning over North Central MT. Some rain likely in
Southwest MT by Monday morning, but precip will not be as heavy
over the Southwest. Expect mountains/passes to be obscured at
times across the CWA by low clouds/precip.

For KGTF: Main concern will be thunderstorm potential between 00z
and 03z this evening. Some storms could have strong erratic wind
gusts or hail. Given current conditions, kept hail out of the
forecast for now. Expect low clouds/light rain Monday morning,
with some improving conditions towards mid day Monday. Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  69  51  64  47 /  20  90 100  40
CTB  62  46  56  44 /  90  90 100 100
HLN  76  51  66  44 /  10  80 100  20
BZN  82  48  69  40 /   0  30  80  10
WYS  75  41  60  30 /   0  90  40  10
DLN  80  46  66  36 /   0  90  50   0
HVR  76  51  68  45 /  60  90 100  90
LWT  77  50  68  44 /  20  90  90  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Flood Watch from 3 PM MDT this afternoon through Tuesday morning
for East Glacier Park Region-Eastern Glacier, Western Toole, and
Central Pondera-Eastern Pondera and Eastern Teton-Eastern Toole
and Liberty-Northern High Plains-Southern High Plains-Southern
Rocky Mountain Front.

&&

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