698
FXUS65 KTFX 191724
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1124 AM MDT Sat Sep 19 2026

Aviation Section Updated.

.KEY MESSAGES...

 - Localized flooding possible in areas with moderate rainfall
   across parts of central and southwest Montana today.

 - Drier and warmer weather pattern develops for the upcoming week

&&

.UPDATE...
/Issued 1022 AM MDT Sat Sep 19 2026/

The Flash Flood Watch for Northwest Beaverhead, which was in place
for the potential of flash flooding on the Sand Creek and Bobcat
Lakes burn scars, has been cancelled as the heaviest rainfall has
moved out of the area. - Moldan

&&

.DISCUSSION...
/Issued 1022 AM MDT Sat Sep 19 2026/

 - Meteorological Overview:

A vertically stacked mid-upper level low, centered over southern
Idaho early this morning, will slowly track east into Wyoming
through tonight while gradually weakening. This setup will sustain a
deep, anomalously moist easterly flow across southwestern Montana
today. Widespread and locally moderate to heavy rain this morning
will concentrate along and south of a deformation/convergence axis
extending eastward across central Montana north of the low.
Conversely, areas north of this axis will experience little to no
precipitation. By this afternoon, rainfall will transition to a more
showery pattern and pivot back southward over southwestern Montana,
following the circulation moving into Wyoming.

As the system continues eastward tonight, a few lingering showers
remain possible across southwestern Montana into Sunday morning as
moisture wraps around its backside. Clearing skies from the west
overnight into Sunday morning may favor fog formation in
southwestern Montana valleys. Upper-level ridging will then rebuild
across Montana and the Northern Rockies by Sunday afternoon,
returning predominantly sunny, warmer, and drier conditions to the
area.

A dry weather pattern with above-normal temperatures is expected
next week. Broad-scale ridging will attempt to build westward across
the CONUS while troughing persists off the West Coast, maintaining
upper-level heights above average under a southwesterly flow regime.
High temperatures in the upper 70s to around 80 are anticipated,
running roughly 10 degrees above early-autumn normals.

 - Forecast Confidence & Scenarios:

An area of rainfall with embedded moderate to locally heavy rates
(0.2 to 0.4 in/hr) will initially focus along the US-12 corridor
early this morning. This precipitation is expected to lift northward
toward the Little Belt and Snowy mountains later this morning before
tapering off. The heaviest rainfall accumulations are anticipated
over and adjacent to the Castle, Big Belt, and Elkhorn mountains,
though confidence is somewhat lower regarding how far north higher
amounts will reach into the Little Belts.

&&

.AVIATION...
19/18Z TAF Period

Rain will continue to drift east across southwest MT through most
of the TAF period. MVFR conditions are likely across terminals
KWYS, KEKS, and KLWT with low ceilings being the primary risk as
the showers shift eastward. Across Central and Northern MT, VFR
conditions will prevail through the TAF period as cloud bases will
remain above the minimums, though a spot shower cannot be ruled
out especially for terminals KGTF and KHVR. As we move into the
overnight hours, uncertainty is high on lingering cloud cover as
the storm system exits east. Terminals KWYS, KBZN, and KEKS are of
highest uncertainty as earlier departure of cloud cover could
allow decreased visibility from fog particularly between 20/08z
and 20/15z. Overall, cloud decks will improve towards the end of
the TAF period moving from east to west giving way to VFR
conditions.
-JR

&&

.HYDROLOGY...

Observed 24-hour precipitation totals have reached up to
approximately 1.00 in northwest Beaverhead County, primarily from
yesterday evening, with 0.500.75 measured so far across parts of
Jefferson, Broadwater, and Meagher counties. Although the risk for
intense rainfall rates is subsiding, the potential for runoff and
debris flow near burn scars persists through this morning. Today,
additional rainfall up to around 1.00 is likely (6090% chance) in
portions of Jefferson, Broadwater, and Meagher counties, where
localized 24-hour totals near or exceeding 2 inches remain possible
(3050% probability). Amounts of this magnitude represent a 1-in-5
to 10-year recurrence interval for this time of year and could
trigger minor urban and rural flooding in poor-drainage areas.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  47  74  47  79 /  10   0   0   0
CTB  43  73  44  76 /   0   0   0   0
HLN  46  72  46  77 /  10   0   0   0
BZN  42  66  40  73 /  40  10   0   0
WYS  31  61  29  68 /  60  10   0   0
DLN  40  67  40  75 /  20   0   0   0
HVR  46  74  46  79 /  10   0   0   0
LWT  45  65  43  75 /  80  30   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through this evening for Big Belt, Bridger and
Castle Mountains-Elkhorn and Boulder Mountains-Little Belt and
Highwood Mountains.

Flood Watch until 6 PM MDT this evening for Canyon Ferry Area-
Gallatin Valley-Helena Valley-Meagher County Valleys.

&&

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