983
FXUS65 KTFX 191143
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
543 AM MDT Sat Apr 19 2025

Aviation Section Updated.

.KEY MESSAGES...

- A cold front will usher in a return to unsettled conditions
  later today through at least the middle of next week, with
  periods of lower elevation rain showers, mountain snow, and
  isolated thunderstorms.

- Afternoon temperatures warm as much as 5 to 10 degrees
  above average today before cooling closer to seasonal averages
  for the remainder of the forecast period.

&&

.DISCUSSION...
/Issued 249 AM MDT Sat Apr 19 2025/

 - Meteorological Overview:

Southwesterly surface winds are increasing along the Rocky
Mountain Front and adjacent high plains this morning as a trough
approaches from the northwest. Expect a mild and breezy to windy
day before the cold front slides southeastward and brings
scattered showers and a northerly wind shift this afternoon and
evening. Aside from a few wind gusts over 40 mph along the Rocky
Mountain Front, there are not too many concerns with today`s winds
and shower activity.

The broad and low amplitude mid- level trough will bring an
extended period of unsettled weather, continuing through at least
the middle of next week, with scattered showers, mountain snow,
and isolated thunderstorms. Precipitation amounts through Sunday
evening will generally range from trace amounts at lower
elevations to around a tenth to a couple tenths an inch in the
mountains. Snow levels will generally be at or above pass level
through Sunday evening and may even rise above 7,000 ft over
Central and Southwest Montana Sunday afternoon due to warm air
advection ahead of the main trough axis.

Then the colder H700/H500 (-10C/-25C) temperatures move in Sunday
night and Monday and lower snow levels back to pass level and
below. Rain and snow amounts do increase on Monday, but the
trough`s broad nature and more diffuse frontogenetic forcing
should limit winter impacts. Although less numerous, scattered
showers, light mountain snow, and isolated thunderstorm activity
will continue Tuesday through Thursday with the aforementioned
trough remaining over the Northern Rockies, albeit in a weakening
state.

Most ensembles continue to highlight a split trough along the
Pacific coast bringing weak southwesterly flow aloft over the
Northern Rockies next Friday. Eventually the trough moves into the
interior west, but its evolution is uncertain at this time.
Currently there is an expectation for at least lower grade
unsettled conditions and near average temperatures heading into
next weekend. - RCG

 - Forecast Confidence & Scenarios:

Rain, snow, and isolated thunderstorms Sunday through Thursday...

Although the trough will take its time passing through the
Northern Rockies, a broader, less amplified system looks to result
in less impactful rain and snow. The steadiest and heaviest
precipitation is expected Sunday night through Tuesday morning
when the trough`s cold pool is overhead and snow levels are
lowest.

The best chance (60 to 90%) for rain/snow amounts in excess of a
half inch/2 inches during this timeframe is currently reserved for
mountain areas. There is also a 70 to 90% chance for 6 inches of
snow or more over the northern portions of the Madison and
Gallatin mountain ranges. Roadway impacts should be mostly
confined to the late night and early morning hours, with the
southwest passes being most susceptible to slushy roadway
accumulations.

In addition to the snow, conditions will also need to be
monitored for isolated thunderstorm activity, especially on Sunday
and Monday with the colder air aloft supporting at least a couple
hundred J/kg of CAPE during the afternoon hours. - RCG

&&

.AVIATION...
19/12Z TAF Period

VFR conditions will generally persist through the first 6 hours of
the TAF period before a cold front arrives this afternoon. After
19/18Z ceilings will gradually start to lower with mountain
obscuration remaining a concern as low-VFR to mid-MVFR ceilings
are expected across much of the region through at least 20/12Z.
Precipitation chances across the region increase after 20/00Z with
precipitation generally remaining light, however, there is a
chance for some temporary MVFR visibilities under heavier showers.
-thor

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  64  38  59  35 /  30  50  40  40
CTB  57  32  52  30 /  80  40  60  30
HLN  63  37  59  35 /  20  50  40  50
BZN  59  34  57  32 /  10  70  50  80
WYS  50  25  50  23 /  10  60  60  70
DLN  58  31  57  31 /  10  80  20  50
HVR  65  36  59  34 /  20  90  50  70
LWT  62  37  55  34 /  10  50  50  80

&&

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

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