612
FXUS65 KTFX 221742
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1142 AM MDT Tue Apr 22 2025

Aviation Section Updated.

.KEY MESSAGES...

- A slow moving Pacific weather system will bring scattered rain
  and snow showers through Thursday night, with the highest
  concentration of rain and snow shifting southward into the
  higher terrain of Central and Southwest Montana.

- Friday will be a drier day before more spring rain, mountain
  snow, and thunderstorms return this weekend into early next
  week.

- Near average temperatures are generally expected for the next
  seven days, warmest on Friday and Saturday.

&&

.UPDATE...
/Issued 1024 AM MDT Tue Apr 22 2025/
Current forecast looks on track. No changes. Brusda

&&

.DISCUSSION...
/Issued 1024 AM MDT Tue Apr 22 2025/

 - Meteorological Overview:

The responsible mid- level low over the Canadian prairies will
continue to move off to the east with a chilly northwesterly flow
aloft left in its place over the Northern Rockies. This will keep
temperatures slightly below average today and maintain a scattered
to broken stratus deck and some scattered rain/snow showers over
the plains for much of the day. There will also be some rain and
snow shower activity in other areas, though the coverage is not
expected to be as high as the last couple of days for most
locations.

Broad Pacific troughing will remain in place through late
Thursday for continued unsettled conditions, though temperatures
will moderate by a few degrees each day. A weak shortwave begins
to deepen over S OR/N CA later today before swinging northeastward
and bringing rain and mountain snow to Central and Southwest
Montana late tonight through Thursday night.

There looks to be a very brief period of upper level ridging
sometime Friday into early Saturday before southwesterly flow
aloft develops ahead of a deepening split trough over the Pacific
coast heading into the weekend. Although there are fairly
significant uncertainties regarding the evolution of this system,
most ensembles support increased showers and some thunderstorm
activity on Saturday with better chances for steadier rains,
mostly mountain snow, and more thunderstorms Sunday into early
next week. Temperatures are favored to warm slightly above average
for the first half of the weekend and then fall back closer to
normal heading into early next week. - RCG

 - Forecast Confidence & Scenarios:

A couple periods of light snow over the higher terrain of Central
and Southwest Montana tonight through Thursday night...

Broad Pacific troughing will continue the unsettled conditions for
much of this week, with periods of lighter end scattered rain and
snow showers throughout the region. The focus of steadier rain and
snow will shift southward into the higher terrain of Central and
Southwest Montana tonight through Thursday night. Probabilistic and
deterministic forecast guidance are both suggesting lower end
accumulations with the best chance (60%+) for 2 or more inches of
snow or more reserved for the higher terrain of Gallatin and Madison
counties for the 48 hour period ending Friday at 6 am MDT. Timing
for potential minor impacts, if any, will be Wednesday morning and
possibly again Thursday morning. Warm air advection aloft should
then raise snow levels and reduce impacts for the remainder of
Thursday and Thursday night.

Widespread rain and mountain snow potential Sunday through next
Tuesday...

This weekend`s weather is heavily dependent the evolution of a
split flow Pacific trough. These scenarios typically lead to lower
forecast confidence and this time is no exception. The latest
ensembles are currently divided with about 60% favoring the
greater portion of moisture and forcing to dive southward into the
Great Basin and southwestern states for lower precipitation
amounts and milder temperatures over the Northern Rockies. The
remaining 40% highlight cooler and wetter solutions with varying
versions of the closed low staying farther north over the interior
west. At the very least, there`s an expectation for periods of
showers, mountain snow, and some thunderstorms, most widespread
Sunday through next Tuesday.

These uncertainties are reflected in the significant differences
between the 50th and 90th NBM forecast rainfall/snowfall
percentiles. The 50th percentile gives a general tenth to quarter
inch of rainfall for lower elevations and around quarter to half
inch of moisture in the mountains, while the 90th percentile is
closer to the half to 1 inch mark at lower elevations and around 1
to 2 inches in the mountains. Similarly, mountain snowfall
amounts for the 50th percentile are generally in the 1 to 4 inch
range and in the 6 to 18 inch range for the 90th percentile. This
situation will be closely monitored in the coming days. - RCG

&&

.AVIATION...
22/18Z TAF Period

The main concern for the TAF period is rain/snow showers across
North-Central MT this afternoon. Highest confidence for
precipitation is at KCTB/KVHR. However, there`s a 20% chance KGTF
and KHLN gets clipped with a brief shower. MVFR ceilings continue
through the afternoon at KCTB and KHVR. Clouds clear across
North-Central MT this evening, which we will have to monitor the
potential for fog development (particularly at KHVR). Breezy
northwest winds continue across the plains during the afternoon
today. -Wilson

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  50  29  57  32 /  20  10  10   0
CTB  46  26  55  29 /  30  20   0   0
HLN  54  31  59  35 /  20  10  10  10
BZN  52  29  53  31 /  20  20  20  20
WYS  47  22  51  24 /  30  30  50  30
DLN  52  30  55  32 /  10  10  10  10
HVR  48  25  58  30 /  40  20  10  10
LWT  47  27  50  30 /  20  20  20  20

&&

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

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