166
FXUS65 KTFX 060938
AFDTFX

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

.KEY MESSAGES...

 - Thunderstorms, some strong to severe, are expected to move
   through Montana tomorrow, 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...

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...
06/06Z TAF Period

North-Central and Central Montana: Low stratus will move in and
linger through most of the night with rain showers possible,
particularly along and west of the I-15 corridor. Generally
MVFR/IFR conditions are expected during this time but there is a
potential for temporary reductions into LIFR should fog/mist start
to develop. A larger concern will be the thunderstorm potential
tomorrow afternoon and evening with the chance for gusty winds and
gusty winds. Thunderstorms are expected to develop after 07/00Z,
starting in the south and quickly moving to the northeast.
Mountain obscuration will be a concern throughout the entire
period.

Southwest Montana: VFR conditions are expected to prevail over the
period with gusty south winds expected to develop in the Madison
River Valley Sunday afternoon. There is a low probability for some
fog developing at KBZN tonight but confidence was not high enough
to include it in the TAF.


For KGTF: MVFR conditions for lower ceilings develop by 06/08Z
with periods of IFR conditions possible between 06/10Z and 06/15Z.
Winds start to gradually pick up out of the north in the early
afternoon and become more northeasterly by 06/23Z. There is a
chance for scattered thunderstorms across the region Sunday
afternoon with a few expected to turn severe. For the KGTF
vicinity there are especially concerns for hail and gusty winds,
with the greatest chance for severe weather expected after 07/02Z.
The crosswind potential is low at this time but the greatest
concerns would be related to the thunderstorm develop expected
later in the day.   -thor

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  72  51  63  46 /  20  90 100  60
CTB  62  46  57  44 /  90 100 100  90
HLN  76  52  65  46 /  10  80 100  20
BZN  82  49  69  41 /   0  60  90  10
WYS  75  40  59  30 /   0  90  70  10
DLN  80  46  66  37 /   0  70  80   0
HVR  76  51  68  46 /  50  90 100  90
LWT  78  50  69  45 /  10  90  90  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
&&

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