715
FXUS65 KTFX 121643
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1043 AM MDT Sat Jul 12 2025

Forecast and Aviation Section Updated.

.KEY MESSAGES...

 - Hot and generally dry conditions expected through the weekend.

 - Chance for isolated thunderstorms along the Hi-Line Sunday
   evening.

 - Cooler and wetter conditions return Monday through Wednesday.

&&

.UPDATE...
Current forecast is on track, no changes planned for this morning.

&&

.DISCUSSION...
/Issued 450 AM MDT Sat Jul 12 2025/

 - Meteorological Overview:

Northwest flow will continue through today and tomorrow with
temperatures warming into the upper 80s to mid 90s across the lower
elevations of north-central, central, and southwest Montana.
Generally dry conditions are expected through the weekend outside
of a 20-30% chance for isolated thunderstorms across the Hi-Line
Sunday afternoon/evening.

A strong cold front pushes through Monday into Tuesday bringing
temperatures across north-central and central Montana down 10 to
15 degrees. There is a chance for widespread rain across much of
north-central and central Montana with more isolated amounts down
into southwest Montana through Wednesday. In the wake of the
trough, temperatures will start to moderate with some warming
expected by the weekend.


 - Forecast Confidence & Scenarios:

Hi-Line Thunderstorms on Sunday:

There are early indications from the RDPS and NAM 3km that there
could be some thunderstorms along the Canadian border Sunday
afternoon/evening with just enough CAPE and shear to cause
problems. In lieu of more hi-res guidance, which does not quite
go out far enough at this time, the most likely scenario is that
most of the thunderstorm activity will stay north of the Canadian
border. However, a few cells may turn south into Montana causing
concern as those tend to be on the stronger side. The main
concerns with any thunderstorm that develops would be strong
winds and hail.


Storm System Monday-Wednesday:

Despite the start of this event only being a couple days out,
there are still some drastic differences in how the models are
handling both the timing and position of the upper level trough
that is expected to move through the region.

To give an idea on the current timing differences, the ECMWF has
the trough axis over western Montana at 00Z Wednesday, the GDPS
has this occurring at 06Z Wednesday, and the GFS has the trough
axis reaching western Montana by 15Z Wednesday. To further add
complications, the 06Z run of the NAM is suggesting the trough
axis reaches western Montana by 09Z Tuesday, 12-24 hours ahead of
the long-range models. Not to mention that while the ECMWF, GDPS,
and NAM agree on the trough digging through much of the state,
which would give us more moisture and higher rainfall amounts, the
GFS flattens out the trough and keeps it generally above the
International border which would almost completely dry out any
potential rainfall in Montana.

As it stands, the NBM is currently taking a middle-of-the-road
approach but leaning on the wetter side of things with most of the
precipitation falling north of a line between Helena and
Lewistown and locations in southwest Montana receiving generally
less than a tenth of a inch.

Forecaster confidence-wise, it seems more of long-range models
are pointing towards a wetter solution with the GFS remaining an
outlier for now. Early indications at the end of the 06Z NAM
confirm that there is fairly good confidence in north-central and
central Montana receiving a wetting rain. Some of the current QPF
amounts seem to be a little high but are not outside the range of
possibilities with this event. The concerning factor is if the
NAM is true, the trough is arriving much sooner than previously
expected which may potentially throw some of the current forecast
out of alignment. Right now, the confidence is that there is a
trough and it will arrive in Montana. Beyond that, the models
still have yet to agree on the finer details on how this event
will play out.  -thor


&&

.AVIATION...
12/18Z TAF Period

VFR conditions will prevail over the CWA through the period. Do
expect mid/high level clouds to continue to move southeast through
the CWA through early evening. Some breezy westerly winds expected
at times this afternoon and early this evening as well. Brusda

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  91  60  94  58 /   0   0   0  10
CTB  85  56  88  55 /   0   0   0  20
HLN  91  58  94  61 /   0   0   0  10
BZN  91  53  94  55 /   0   0   0  10
WYS  81  41  85  44 /   0   0   0  10
DLN  87  51  90  53 /   0   0   0  10
HVR  91  58  94  59 /   0   0   0  20
LWT  85  55  90  55 /   0   0   0  10

&&

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

&&

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