474
FXUS65 KTFX 171044
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
444 AM MDT Thu Jul 17 2025

Aviation Section Updated.

.KEY MESSAGES...

- Slight chance for fog this morning mainly across the North
  Central Montana Plains.

- Scattered showers and thunderstorms across North Central MT
  this afternoon and evening, with hail and strong winds being the
  primary threats.

- Low end chances for showers and thunderstorms this weekend.

&&

.DISCUSSION...
/Issued 200 AM MDT Thu Jul 17 2025/

 - Meteorological Overview:

Low level moisture lingering from the recent system and weak
subsidence in place this morning will allow for the slight chance
for fog development mainly across the North-Central MT plains.
Fog that does develop is expected to clear out by late morning.
Instability and moisture builds in for the afternoon. A small
shortwave aloft moving through late afternoon and evening will
allow for the development of scattered showers and thunderstorms
across the Hi-line and portions of North-Central MT. Increasing
deep layer shear should allow for isolated severe storms, with
hail and strong winds as the main hazards. For Friday, another
shortwave moves through, which will allow for isolated to
scattered showers and thunderstorms across Southwest MT along and
south of I-90. Deep inverted V`s will help bring an isolated
strong wind threat with storms.

Zonal flow aloft continues through the weekend, which will keep
low end precipitation chances mainly in Central MT. Saturday`s
best chances look for strong to severe thunderstorms look to stay
off into Eastern MT, but any westward shifts in precipitation can
increase thunderstorm chances for Central MT. Temperatures
continue to gradually warm back close to normal through the rest
of the weekend. Ensembles hint at a troughing pattern for next
week, which will keep precipitation chances in the forecast, but
disagreements on the evolution of this troughing pattern makes
any details about precipitation unclear at this time.

 - Forecast Confidence & Scenarios:

For fog this morning, hi-resoltution models show a 20-30% chance for
fog development across North-Central MT. Soundings show the best
support for fog development along the Rocky Mountain Front. Winds
will be a limiting factor for fog development, as other area may
see a lower cloud deck instead of fog.

For thunderstorms this afternoon, hi-resoultion models still support
for the potential for strong to severe storms along North-Central
MT. Although CAPE is relatively modest (less than 1,000 j/kg), an
increase in moisture (PWATS ~0.8") and deep layer shear (~50kts
of 0-6km) in similar timing with the shortwave moving through,
supports an environment for at least a few storms to produce hail
of 1" or greater, and/or 58mph or greater wind gusts. Best window
for thunderstorm development looks to be late afternoon and early
evening with the current shortwave timing. The best corridor for
strong to severe storms will be along and north of the Highway 2
corridor. However, showers and thunderstorms can develop as early
as early afternoon.

Thunderstorms Friday look be be mainly confined along and south
of the I-90 corridor. Deep inverted V sounding profiles and 1,000
j/kg of DCAPE do support the potential for a few stronger wind
gusts with storms. Precipitation chances for the weekend overall
is low/isolated across the region. -Wilson

&&

.AVIATION...
17/12Z TAF Period

The initial concern this TAF period will be for patchy fog
across portions of the plains this morning. Any fog that forms
looks to diminish by mid-morning. Attention then turns to the Hi-
Line and vicinity in the afternoon and early evening, where
thunderstorms capable of hail, lightning, and gusty and erratic
winds will develop. -AM

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  81  53  82  55 /  10  10   0   0
CTB  73  47  77  52 /  40  30   0   0
HLN  88  53  88  55 /   0   0   0   0
BZN  89  49  90  52 /   0   0  10  10
WYS  81  41  81  43 /   0  10  30  20
DLN  86  47  87  50 /   0   0  10   0
HVR  81  52  79  55 /  40  50   0  10
LWT  78  49  78  53 /  10  10  10  10

&&

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

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