104
FXUS65 KTFX 170615
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1215 AM MDT Thu Sep 17 2026

.KEY MESSAGES...

 - Trending warmer today, with several rounds of showers and a
   few thunderstorms across Southwest MT and vicinity today.

 - Showers and thunderstorms become more numerous and spread
   further north Friday, with a few being capable of strong wind
   gusts, small hail, and at least briefly heavy rain.

 - Precipitation continues into Saturday in most areas before a
   dry stretch begins Sunday into at least Monday.

&&

.DISCUSSION...

 - Meteorological Overview:
An upper level low meandering in the vicinity of northern CA is
resulting in an increasingly southerly flow aloft across the
Northern Rockies. The first of several weaker embedded waves will
begin moving through this morning, resulting in an initial round of
showers and perhaps a couple thunderstorms across SW MT. While
several additional rounds of showers and thunderstorms look to move
across similar areas through the day today, the strength of any
thunderstorm that develops this afternoon will be dictated by how
much instability will be able to develop between rounds of
precipitation.

Stronger forcing, as well as better thermodynamics and perhaps
kinematics arrive for Friday as the core of the upper disturbance
approaches. Whether or not shear will be sufficient for a more
organized severe weather threat remains to be seen. That said,
should the shear be lower, that would result in a slower storm
motion and result in an increased risk for excessive rainfall
leading to flash flooding given the increased precipitable water
values across the region. Trends will continue to be monitored.

The core of the upper disturbance finally moves overhead Saturday
and eventually eastward Saturday night. Additional precipitation
accompanies this passage in most areas, though areas west of Shelby
to the Rocky Mountain Front are looking to remain dry Saturday.

Although the upper level pattern gets messy to close out the weekend
into early next week, confidence remains high in Sunday and Monday
being dry and on the warm side. Thereafter confidence in the
evolution of the pattern becomes quite low. -AM

 - Forecast Confidence & Scenarios:
Thunderstorms the next few days:

While confidence is high that showers and thunderstorms will develop
over the next few days, confidence in just how much instability
develops remains on the lower side. Relatively strong forcing will
accompany the passage of this system, particularly on Friday. This
forcing may ultimately result in a convective initiation that is a
bit too early to maximize daytime heating, resulting in ample cloud
cover across much of the region by mid-afternoon that limits
thunderstorm strength. -AM

&&

.AVIATION...
17/06Z TAF Period

Generally quiet conditions expected overnight, with mainly just
some increasing clouds over Central/Southwest MT. Low level wind
shear is still possible around Bozeman through about 08z.
Otherwise, expect showers/thunderstorms to develop over Southwest
MT and along the divide later this morning and into the afternoon
hours, with thunderstorms pushing up into Central MT by this
evening. Mountains/passes will be obscured at times starting
later this morning as showers/thunderstorms move through. Brusda

&&

.HYDROLOGY...
Precipitable water approaches an inch at times today through
Saturday over the CWA. This high water content, combined with the
potential for slow moving thunderstorms could result in some
flooding impacts. A minor risk for flash flooding is possible over
much of the CWA on Friday, and over the eastern portions of the
CWA on Saturday. Some burn scar areas northwest of Dillon and the
Horse Gulch burn scar east of Helena could also see some impacts.
Thus it is possible that some flood statement might be needed at
times over the next few days. Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  74  50  74  51 /   0  20  20  60
CTB  69  47  69  46 /   0  20  10  10
HLN  79  50  75  52 /  20  40  60  90
BZN  78  48  74  46 /  30  20  80 100
WYS  71  39  67  36 /  70  50  90  80
DLN  78  47  70  44 /  50  30  90  90
HVR  78  49  77  49 /   0  10   0  10
LWT  78  50  75  48 /   0   0  30  90

&&

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

&&

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