632
FXUS65 KTFX 041117
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
517 AM MDT Mon Aug 4 2025

Aviation Section Updated.

.KEY MESSAGES...

- Showers and thunderstorms will move south to north this
  afternoon through early Tuesday, some may be strong to severe
  with localized strong wind gusts, hail, and heavy downpours.

- Drier conditions are expected for the mid- week period before
  another Pacific trough brings more scattered showers and storms,
  breezy to windy conditions, and cooler temperatures for the
  second half of the work week.

&&

.DISCUSSION...
/Issued 351 AM MDT Mon Aug 4 2025/

 - Meteorological Overview:

Southwesterly flow aloft continues to bring an initial wave of
isolated showers, virga, and some thunderstorms to Southwest and
portions of Central/North-central Montana early this morning. A
Pacific trough currently centered over Oregon will swing
northeastward into the Northern Rockies by tonight. H500 winds
increase to the 40 to 50 kts range ahead of this feature and will
interact with the diurnal instability for scattered to numerous
shower and thunderstorm development this afternoon into tonight.
ML CAPE values look to range form around 500 to 1,000 J/kg in the
southwest to over 1,500 J/kg along the Hi-Line. Similarly PWATS
will be near an inch up north and as low as a half inch over the
southwest. Strong, gusty winds will be the primary thunderstorm
hazard with instances of hail and heavy downpours highest over the
plains east of I15.

Some shower and thunderstorm activity may linger over the plains
Tuesday, especially in the Milk River Valley area, but drier and
breezy conditions are generally expected for Tuesday and Wednesday
in the wake of the departing trough. Ensembles are coming into
agreement with another Pacific trough moving through the Northern
Rockies Thursday through early Saturday. Breezy to windy
conditions, increased shower and thunderstorm activity, and
temperatures cooling as low as 10 to 20 degrees below average are
expected while the trough moves its way through the region.

Ensembles remain in agreement with a progressive northwesterly
flow aloft settling in for the weekend into early next week, but
there are discrepancies on the depth and timing of the troughs and
ridges moving within it. Overall, there`s an expectation for
warming and drying conditions, but deeper troughs would bring
interruptions to this trend in the form of brief cool downs and
increased shower and thunderstorms chances. - RCG

 - Forecast Confidence & Scenarios:

Strong to severe thunderstorm concerns this afternoon through
Tuesday...

Scattered to numerous showers and thunderstorms will initiate
over western and southwestern Montana by the early afternoon hours
before moving north and eastward towards the plains and valleys
later in the afternoon and evening hours. Strong thunderstorm wind
gusts and lightning will be the primary hazards with most
locations having a 70 to 90% chance for gusts exceeding 35 mph
according the 00Z HREF. The latest deterministic CAMS have been
trending upward as well, with swaths of scattered 45 to 60 mph
gusts, mostly for Southwest and Central/North-central locations
north of I90 an east of I15. An increase in moisture and
instability going northward looks to increase the instances of
large hail and heavy downpours as well, mostly for Central/North-
central locations east of I15. Storm motions mostly 20 kts and
greater should limit he residence time of showers and storms, but
half to 1 inch per hour rainfall rates are plausible given the
higher moisture levels, particularly for locations along the Hi-
Line.

Shower and storm activity will diminish and end by midnight for
most areas. The one exception to this will be along the Hi-line
where peak convection will begin later in the evening and persist
through Tuesday morning. Additionally lingering moisture and
instability will be supportive for another round of activity
Tuesday afternoon, particularly for Hill and Blaine counties.

Increased shower and thunderstorm activity, breezy to windy
conditions, and cooler temperatures Thursday through Saturday...

A Pacific trough will move through the Northern Rockies Thursday
through early Saturday. Southwesterly flow aloft develops ahead of
the approaching system late Wednesday into Thursday and brings
breezy to windy conditions for most locations. The strongest winds
look to occur along the Rocky Mountain Front and the higher
terrain and north to south oriented valleys valleys of Southwest
Montana Thursday and Thursday night. The latest NBM probabilities
do not exceed 50% for 45 mph gusts or higher, which compliments
H700 winds generally in the 30 to 35 kt range. Shower and
thunderstorm activity looks to be most widespread Thursday and
Friday while afternoon temperatures run as low as 10 to 20 degrees
below average. - RCG

&&

.AVIATION...
04/12Z TAF Period

Initial concerns will be for a few northward moving showers and
thunderstorms this morning, most notably near the KHVR area. The
most widespread showers and thunderstorms will initiate over West
and Southwest Montana by around 04/18Z and will move north and
eastward through the remainder of the region later in the
afternoon and evening. Gusty winds, hail, and MVFR downpours will
be the primary concerns in addition to lightning. Most storm
activity should diminish and end by around 05/06Z, but some of
this activity may persist well into the overnight hours and even
into Tuesday morning, mostly along the Hi-Line. - RCG

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  85  55  78  54 /  40  70  20   0
CTB  79  53  73  51 /  30  60  30   0
HLN  84  55  81  55 /  60  80  10   0
BZN  86  48  83  49 /  40  50  10   0
WYS  80  38  75  37 /  30  40   0   0
DLN  80  46  78  46 /  40  40   0   0
HVR  88  58  79  55 /  30  90  50  10
LWT  83  51  74  51 /  40  80  20   0

&&

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

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