725
FXUS65 KTFX 190519
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1119 PM MDT Mon Aug 18 2025

Aviation Section Updated.

.KEY MESSAGES...

 - Hot Tuesday, hottest across the plains east of I-15.

 - Still quite warm Wednesday.

 - Trending cooler into Thursday behind a cold front.

&&

.UPDATE...
/Issued 737 PM MDT Mon Aug 18 2025/

Evening update has been published, with the primary adjustment
(albeit relatively minor) being to nudge PoPs closer to latest
radar trends through the remainder of the evening hours. Otherwise
the remainder of the forecast remains on track, with isolated
showers and storms lifting to the northeast from Southwest Montana
and into Central Montana at approximately 20-30 mph. So far this
evening most showers have generally produced little to no
rainfall and wind gusts of 25-35 mph, with the "strongest"
thunderstorms producing rainfall rates of 0.1-0.3"/hr and
gusty/erratic winds of 35-45 mph. - Moldan

&&

.DISCUSSION...
/Issued 737 PM MDT Mon Aug 18 2025/

 - Meteorological Overview:

Upper level troughing off the BC coast is resulting in a weakly
cyclonic southwesterly flow aloft across the region early this
afternoon. This southwesterly flow becomes increasingly anti-
cyclonic however as a building ridge across the interior
west/Central CONUS nudges into the region. This will result in
rising H5 heights over the next day or so. Although height rises and
a transition to a more anti-cyclonic flow aloft are moving in, there
is still enough support for scattered showers and thunderstorms
through the remainder of the afternoon and evening across Southwest
and Central Montana. Gusty winds are the main concern with the
strongest thunderstorms that form.

Transitioning into Tuesday, the rising H5 heights/building ridge
will allow temperatures to rise well above average, hottest over the
plains of eastern Fergus and Blaine counties and vicinity. Given
the forecast brevity of the greatest heat, we will continue to
hold off on heat advisories for the time being.

As quickly as the ridge builds in it will begin to exit equally as
quickly heading into Wednesday. By Wednesday morning H5 heights
begin falling across the region ahead of an approaching upper level
troughing that has been hanging out off the BC coast. Although this
is the case, Wednesday still looks to be on the warm side, with the
hottest temperatures again looking to be in Fergus/Blaine counties
and vicinity.

While showers and thunderstorms do not look to be more than isolated
in nature Tuesday and Wednesday, any that do form would be capable
of producing gusty winds.

Heading into Wednesday night and early Thursday, a cold front looks
to move across the region. There are some discrepancies in timing of
the front as well as the magnitude of winds/gusts that come with it,
but there is higher confidence in it moving through at a time that
would be less conducive to stronger thunderstorms. Cooler
temperatures follow for Thursday and Friday, coolest over the plains
near the Canadian border.

Thereafter another ridge looks to build in across the interior west,
allowing temperatures to trend back closer to, if not a touch above
average. Given the apex of the ridge looks to extend well into
Canada this weekend and Monday, it appears that enough monsoonal
moisture will work northward from the desert Southwest to result in
daily afternoon and evening showers and thunderstorms across
Southwest Montana. -AM

 - Forecast Confidence & Scenarios:

Overall, the chance for a high of 100F on Tuesday is less than 40%
outside of areas near the Missouri River Breaks. Further, the
chance for a low of 70F or higher is only 20% near the Missouri
River Breaks. Given this area of hottest temperatures is
relatively confined in addition to temperatures falling into at
least the 60s overnight, providing relief from stressful
temperatures, no Heat Advisories are being issued with this
forecast package. Trends will continue to be monitored for any
uptick in daytime highs or overnight lows, necessitating a Heat
Advisory. -AM

&&

.AVIATION...
19/06Z TAF Period

VFR conditions will persist through the period as high pressure
builds over the region. There is around a 15% chance for isolated
thunderstorms later in the afternoon on Tuesday which may impact
KCTB, KHVR, and KGTF. However, confidence in timing was not high
enough to include it in the TAF.  -thor

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

&&

.FIRE WEATHER...

Fire weather concerns will continue through Tuesday and Wednesday
with highs in the 90s expected across the plains and valleys across
the region. Minimum RH values will range from the single digits to
the mid teens with Tuesday expected to be the warmest and driest day
of the week. Winds are less of a concern these days, however, an
isolated afternoon dry thunderstorm cannot be ruled out which will
keep fire weather concerns elevated until a cold front passes
through late Wednesday into Thursday. -thor

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  57  96  60  92 /  20   0  20   0
CTB  51  89  59  87 /  10  10  20   0
HLN  56  96  59  92 /  40   0   0   0
BZN  51  97  54  93 /  20   0   0   0
WYS  38  86  43  85 /  10   0   0  20
DLN  48  92  52  89 /  20   0   0   0
HVR  57  95  62  93 /  10   0  20   0
LWT  57  93  57  87 /  20   0   0   0

&&

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

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