147
FXUS65 KTFX 262050
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
250 PM MDT Sat Apr 26 2025

.KEY MESSAGES...

 - Showers and thunderstorms in the afternoon and evening both
   days this weekend will give way to a more widespread
   precipitation Sunday night into Monday, mostly across Southwest
   Montana.

 - Impactful mountain snow is forecast Sunday night into Monday across
   portions of Southwest Montana, with lower confidence in
   impactful snow at and below pass level in similar areas.

 - After another brief shot of precipitation chances will be
   around Tuesday into Wednesday before a warming a drying trend
   is forecast for the latter half of next week.

&&

.DISCUSSION...

 - Meteorological Overview:

A closed upper low over CA is resulting in a southerly flow aloft
across the region this afternoon. This southerly flow is helping
send temperatures at least a few degrees warmer compared to
yesterday, which combined with sufficiently cool air aloft, is
resulting in showers and thunderstorms across the region this
afternoon. The expectation is for these to continue
north/northeastward through the early evening before dissipating by
late evening. Forecast soundings show relatively deep mixing in
areas, which would be conducive to gusty winds developing from
decaying showers and thunderstorms. At this point the risk for gusts
in excess of 50 mph appears quite low.

The aforementioned upper low over CA will shift northeastward toward
WY tonight into Sunday, helping dig out a surface low somewhere over
eastern WY over the same timeframe. This developing surface low will
begin the transition to cooler conditions across the region,
initially over the plains behind a Canadian cold front Sunday
morning. Gusty winds are likely behind this front, especially in
valleys prone to gusty winds. Before the cold front arrives in
Southwest Montana tomorrow, there looks to be sufficient instability
for another opportunity for showers and thunderstorms. This window
is relatively short lived however, as by the late afternoon
precipitation will begin its transitions to be more stratiform in
nature as the upper level disturbance passes just off to the
southeast.

As the colder air arrives behind the cold front and precipitation
across Southwest Montana transitions to become more widespread in
nature the big question becomes just how quickly snow levels fall
across the region. There continues to be a split camp in thinking,
with the NAM and GFS crashing snow levels via cold air advection and
dynamic cooling from precipitation, while the Canadian and European
are slower to lower snow levels and thus keep snow in the mountains.
It needs to be said that they agree on impactful precipitation
amounts across Southwest Montana, the disagreement is just on
precipitation type at and below pass level.

Precipitation further north looks to be lighter, but will still
result in a period of lighter snow in the mountains of Central
Montana late Sunday night into Monday, and perhaps in northerly
upslope areas at lower elevations across Central Montana as well.

This system quickly departs late Monday morning, though light
lingering precipitation will be possible into the early afternoon
hours.

Heading into Tuesday and Wednesday, a northwesterly flow aloft will
be in place as ridging build in off to the west. A weak wave passing
through the building ridge will yield an opportunity for additional
precipitation, though amounts with this system will be much lighter.

The building ridge shifts eastward for the latter portion of the
week, allowing for a drier period and much warmer conditions to
develop. Uncertainty increases toward next weekend, with the
potential for another cooler period with increased precipitation
chances. -AM

 - Forecast Confidence & Scenarios:

Greatest uncertainty continues to remain with respect to snow levels
in the Bozeman and Ennis area Sunday night into Monday. More
aggressive models such as the NAM and GFS crash snow levels quick
enough for a period of high impact snowfall down into much of the
Gallatin Valley. Meanwhile guidance that is slower to get the cooler
air in the area keeps precipitation type as rain through the whole
event. These two scenarios are drastically different from an impact
perspective, and neither can be discounted. For now I have elected
to not issue Winter Storm Watches or Winter Weather Advisories for
any additional areas, though the picture may change very quickly if
either model camp trends toward the other. Those at lower elevations
of Southwest Montana, particularly in the Gallatin and Madison River
Valleys, should be prepared for the potential for sharp changes in
the forecast toward higher snowfall amounts. -AM

&&

.AVIATION...
26/18Z TAF Period

The initial concern this TAF period will be for a period of
scattered showers and thunderstorms this afternoon and evening
across the region. Gusty and erratic winds are the primary concern
with thunderstorms today. After a more benign period tonight, a cold
front then begins moving south out of Canada tomorrow morning,
bringing a period of gusty northerly winds and low clouds. -AM

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  41  62  34  57 /  30  40  60  20
CTB  38  54  31  57 /  20  10  20  10
HLN  43  63  37  59 /  20  60  80  30
BZN  37  64  32  54 /  10  90 100  70
WYS  26  58  29  51 /   0  70 100  80
DLN  37  61  35  55 /  20  80 100  40
HVR  40  69  31  59 /  20  30  20  10
LWT  40  63  32  49 /  30  60  90  40

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 6 PM Sunday to noon MDT Monday for
Gallatin and Madison County Mountains and Centennial Mountains.

&&

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