251
FXUS65 KTFX 182338
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
538 PM MDT Fri Apr 18 2025

Aviation Section Updated.

.KEY MESSAGES...

- A Pacific cold front will bring more unsettled conditions late
  Saturday through at least the middle of next week, with lower
  elevation scattered rain showers, mountain snow, and a few
  thunderstorms.

- Temperatures warm as much as 5 to 10 degrees above average on
  Saturday before cooling closer to seasonal averages for the
  remainder of the period.

&&

.DISCUSSION...
/Issued 256 PM MDT Fri Apr 18 2025/

 - Meteorological Overview:

Transient ridging quickly passes through the Northern Rockies
later through much of Saturday for mild and dry conditions before
a Pacific cold front ushers in another period of unsettled
conditions later Saturday afternoon and evening. Southwest to
westerly winds increase tonight and on Saturday along the Rocky
Mountain Front and the plains, but wind speeds will mostly stay
below 40 mph except for the normally windier spots along the
Rocky Mountain Front and the neighboring high plains.

Scattered shower activity is expected along and behind the front
along with a northerly wind shift. Snow levels will be above
6,000 ft and rainfall/snow melt equivalent amounts will generally
range from trace amounts at lower elevations to around a tenth of
an inch or so in the mountains. Additional periods of showers,
mostly mountain snow, and isolated thunderstorms are expected
Sunday through Tuesday as the main trough slowly traverses the
Northern Rockies.

Southwesterly flow head of the trough`s arrival on Sunday may
send snow levels climbing to the 7,000 to 8,000 ft level on
Sunday before the colder H700/H500 (-10C/-25C) temperatures move
in Monday and Tuesday. With this trough being more broad in
nature and having more diffuse frontogenetic forcing, snowfall
amounts and associated winter impacts are expected to on the
minor side.

Most ensembles show a varying degree of troughing over the
Pacific Northwest with a weak southwesterly flow over the
Northern Rockies for the second half of next week. This should
maintain lower grade unsettled conditions with scattered shower
activity and near average temperatures. - RCG

 - Forecast Confidence & Scenarios:

Rain, snow, and isolated thunderstorms late Saturday through
Tuesday...

Although the trough will take its time passing through the
Northern Rockies, a broader, less amplified system looks to
result in less rain and snow and associated winter weather
impacts. The heaviest snow is expected Sunday night through
Tuesday morning when the trough`s cold pool is overhead and snow
levels fall down to the plains and valleys. The best chance (70
to 80%) for rain/snow amounts in excess of a quarter inch/2
inches during this timeframe is currently reserved for mountain
areas. Roadway impacts should be mostly confined to the late
night and early morning hours. In addition to the snow,
conditions will also need to be monitored for isolated
thunderstorms, especially on Sunday and Monday with the colder
air aloft supporting at least a couple hundred J/kg of CAPE each
afternoon. - RCG

&&

.AVIATION...
19/00Z TAF Period

Through around 19/15Z, high pressure aloft will continue VFR
conditions with mostly clear skies and light winds for North
Central, Central, and Southwest Montana; however, low-level wind
shear will be a concern along the Rocky Mountain Front (including
the KCTB terminal area).

After 19/15Z and through 20/00Z, a disturbance approaching the
area from the northwest will move a weak cold front through the
area. This should increase west-northwest winds overall, causing
mountain wave turbulence. Ceilings will also gradually lower with
mountain top obscuring precipitation on the Continental Divide,
with some areas over the plains having low VFR to possibly high
MVFR ceilings. -Coulston

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  35  64  37  60 /   0  10  20  50
CTB  35  56  33  52 /   0  10  10  50
HLN  33  63  37  58 /   0   0  20  40
BZN  21  58  32  57 /   0   0  40  50
WYS  10  50  25  50 /   0   0  30  60
DLN  24  58  31  57 /   0   0  20  20
HVR  30  65  35  60 /   0   0  30  50
LWT  27  61  37  55 /   0   0  20  60

&&

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

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