343
FXUS65 KTFX 031502
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
902 AM MDT Sun Aug 3 2025

.KEY MESSAGES...

 - Showers and thunderstorms will be less widespread today, with
   the main focus near the Hi-Line and near the ID border.

 - Thunderstorms become more widespread again Monday afternoon
   and evening, with an increased risk for severe thunderstorms.

 - Confidence increasing in a briefly cooler period Friday and
   Saturday, with daytime highs largely in the 70s at lower
   elevations.

&&

.UPDATE...

Today there will be isolated showers and thunderstorms along the
Hi-line and the Montana/Idaho Border in Southwestern Montana with
everywhere else being dry. For the update, temperatures across
North-central Montana were increased to better reflect current
observations and trends and the latest hi-res model guidance.
PoPs today across the Hi-Line were increased to better reflect
current radar imagery and the latest hi-res model guidance. PoPs
across Southwestern Montana this afternoon and evening were
increased to better reflect the latest hi-res model guidance. The
rest of the forecast is on track. -IG

&&

.DISCUSSION...
/Issued 519 AM MDT Sun Aug 3 2025/

 - Meteorological Overview:

A rather messy initial setup will trend more clear heading into
Monday. To start, an upper level ridge is in place well off to the
south across the Southwest CONUS. The result is for a southwesterly
flow aloft across the Pacific NW (Just ahead of troughing off the
Pacific coast) that transitions to be more zonal over the
Northern Rockies as of writing this discussion. Further, an
embedded pocket of vorticity appears to be in place across
southern AB/SK in the mid and upper levels. As today unfolds, the
lingering vorticity near the Hi-Line and increasingly
southwesterly flow aloft ahead of the aforementioned trough across
far SW MT will support a split precipitation chance scenario,
with Central MT looking largely dry.

The AB/SK vorticity eventually does kick away from the region, but
not before resulting in showers and thunderstorms near the Hi-Line
again today. Shear in this area looks to be rather weak, resulting
in a more pulsey-type shower and thunderstorm scenario. HREF
ensemble mean surface based CAPE in excess of 1,000 m2/s2 indicates
that although shear is low, sufficient instability may be able to
briefly result in some larger hail, especially where dew points
exceed 60 F today (Maximizes instability). Forecast soundings do not
show large DCAPE, but when shear is this low, there is always at
least a localized risk for gusty winds from decaying thunderstorms.
This activity looks to be diurnally drive, fading around and after
sunset.

Meanwhile across SW MT the aforementioned southwesterly flow and
associated troughing will be a bit delayed compared to peak diurnal
heating. As a result, the timeframe for showers and thunderstorms
looks to be later in the afternoon into the evening. Forecast
soundings show deep inverted-V`s across SW MT this afternoon and
evening, supporting a gusty wind threat from thunderstorms that do
form before sunset. Forcing continues into the overnight across
Southwest Montana and into portions of Central Montana, which will
result in some elevated showers and thunderstorms well after
sunset.

Heading into Monday the main wave of the aforementioned troughing
moves across the Northern Rockies, and looks to be favorably timed
with diurnal heating. Showers and thunderstorms look to initially
form across terrain, shifting northeastward with time through the
afternoon into the evening Monday. A gusty wind threat will be in
place across Southwest Montana, where modestly deep inverted-V
profiles will promote mixing of stronger winds aloft to the ground
in thunderstorms. Further north on the plains surface moisture is a
bit better. While stronger flow aloft is a bit later to arrive on
the plains (Delayed increase in shear) it still looks sufficient for
at least loosely organized clusters of thunderstorms. Wind would be
the primary threat, with a non-zero risk for larger hail as well.
This activity moves northeastward into Monday evening, though may
linger across northern areas well into Monday night.

As the troughing continues northeastward, away from the region
Tuesday, a few lingering showers and thunderstorms look to stick
around near Hill and Blaine counties and vicinity into early
Tuesday afternoon. Otherwise, the region is looking mainly dry for
Tuesday.

Shortwave ridging within southwesterly flow aloft Wednesday looks to
yield a dry day across the region, though by Wednesday evening the
flow becomes increasingly cyclonic. Hence, there is still a small
opportunity to eek out a shower Wednesday evening.

Thereafter ensembles favor a period of troughing across the Northern
Rockies late week into the weekend. A cooler period is favored
toward the weekend, with low-end precipitation opportunities
returning. -AM

 - Forecast Confidence & Scenarios:

The bulk of the uncertainty is related to late week. While both
deterministic guidance and ensembles favor troughing, deterministic
guidance is struggling with timing of any embedded waves, as well as
with how many more prominent waves will develop. Timing and strength
of each of these waves will ultimately determine how cool the region
gets each of Friday and Saturday, as well as dictate precipitation
chances. -AM

&&

.AVIATION...
03/12Z TAF Period

Patchy fog can`t be ruled out over the some of the more fog prone
river valleys and wind protected areas through 03/15Z, mostly near
KWYS. Otherwise, drier westerly flow aloft will maintain general VFR
conditions over the next 24 hours. There will still be a few stray
showers/storms along the Hi-Line this afternoon and evening. Then a
trough moving into the Pacific Northwest will bring a more unstable
southwesterly flow aloft over the Northern Rockies tonight into
Monday. Isolated high based convection will initiate over far
Southwestern Montana after 03/20Z before crossing I90 and heading
into Central/North-central Montana during the overnight hours into
Monday morning. - RCG

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  86  56  85  55 /   0   0  20  60
CTB  80  51  78  53 /  30  10  20  50
HLN  88  57  85  54 /   0  20  40  60
BZN  86  51  87  48 /   0  20  20  40
WYS  77  39  80  37 /  30  30  20  30
DLN  81  48  81  44 /  20  30  30  40
HVR  85  57  87  57 /  30  20  20  70
LWT  81  54  84  51 /  10  10  20  70

&&

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

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