013
FXUS65 KTFX 160134
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
734 PM MDT Tue Sep 15 2026

.KEY MESSAGES...

 - Areas of rain near the Canadian border late today into tonight.

 - Dry conditions Wednesday ahead of showers/thunderstorms
   Thursday afternoon through Friday night.

 - Warmer and drier conditions by the end of the weekend.

&&

.UPDATE...

The main changes to the forecast was to increase coverage of PoPs
across North-Central MT. Current radar shows light isolated
showers initiating due to a small boundary. Light rain is expected
to continue across parts of North-Central MT through early
Wednesday morning, but coverage of rain greatly drops off around
midnight. There is a low end chance for patchy fog Wednesday
morning, but lower clouds may prohibit development. -Wilson

&&

.DISCUSSION...
/Issued 542 PM MDT Tue Sep 15 2026/

 - Meteorological Overview:

Due to an upper-level trough clipping north MT, there will be areas
of light rain showers this evening through the early hours of
Wednesday morning. However, showers are expected to be limited to
north central MT and the north Rockies.

Wednesday will be a break between the two upper level troughs as
weak upper level ridging will be present. As such, conditions will
be dry and mild for the majority of the state.

During Tuesday night and Wednesday, the trough that has been sitting
stagnant over the PNW will develop a closed off low and begin
shifting eastward. This eastward movement will cause upper level SW
flow to develop over MT on Wednesday. The upper level SW flow is
expected to continue through Saturday as the upper level low
continues its eastward track across the state.

Although upper level SW flow is expected to develop Wednesday,
warmer weather and the potential for showers/thunderstorms are
expected to hold off until Thursday. Looking at Thursday and beyond,
warmer weather and the potential for showers/thunderstorms will
continue through Friday night. By midday Saturday, the potential for
showers/thunderstorms will have ended as the low makes continues its
eastward track across the state.

Beginning Sunday, a period of warmer and drier conditions will
develop and is expected to continue into the beginning of the
following week. - ESH

 - Forecast Confidence & Scenarios:

Thunderstorms on Thursday and Friday...

CAPE and shear per ECMWF EFIs will climb to between 0.6 and 0.75
along and south of the I-90 corridor on both Thursday and Friday,
with Friday having the greatest coverage of EFIs in excess of 0.6
across the aforementioned region. BUFKIT soundings across Southwest
Montana indicate high cloud bases in excess of 10kft, with very dry
air beneath these bases (i.e. inverted-Vs). This dry air combined
with climatologically unusual, with respect to September
climatology), instability and shear would lend to the idea that a
few thunderstorms that develop on either day would be capable of
producing strong and erratic outflow winds. BUFKIT soundings also
indicate tall and skinny CAPE profiles across Southwest and portions
of Central Montana, which when considered against PWATs of 2-3
standard deviations above normal (or between 0.75" to 1") suggests
the potential for some thunderstorms to produce heavy rainfall. -
Moldan

&&

.AVIATION...
16/00Z TAF Period

A weather system near the MT and Canada border will continue to
bring a swath of clouds to North-Central MT and isolated light
rain showers along the Hi-line this evening. Cloud ceilings will
lower overnight into Wednesday morning across North-Central MT,
with some areas reaching down to MVFR ceilings and to IFR at
KCTB. Ceilings will rise again during the morning hours, with
clouds clearing throughout the afternoon. -Wilson

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  43  62  42  72 /  20   0   0   0
CTB  43  58  39  68 /  70  20   0   0
HLN  44  67  44  78 /  10   0   0   0
BZN  38  71  40  77 /   0   0   0  20
WYS  28  74  37  71 /   0   0  30  70
DLN  37  72  42  77 /  10   0  10  30
HVR  44  65  42  75 /  50  10   0   0
LWT  40  64  42  76 /  20   0   0   0

&&

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

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