673
FXUS65 KTFX 050504
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1004 PM MST Tue Feb 4 2025

Aviation Section Updated.

.KEY MESSAGES...

 - Periods of moderate to heavy snow continue through Wednesday
   across Central to North-Central, with convective snow showers
   possible across the Southwest MT Wednesday.

 - Cold air lingers through most of the area through Wednesday,
   with hazardous windchills across the Rocky Mountain Front and
   northern plains tonight.

 - Temperatures improve late this week, but the pattern will
   remain cold and snowy through the forecast period.

&&

.UPDATE...

Main update to the overnight forecast period was to delay the
shift to more gusty southerly winds south of Interstate 90 until
after 3 am. Otherwise, snow is forecast to overspread much of the
forecast area again after midnight.

Winter weather highlights remain as is, but recalculation of wind
chills shows a good chance for -30F wind chills at times as
farther east on the Hi-Line into Hill and Blaine Counties and
south into Chouteau and Cascade Counties and into the Helena and
Canyon Ferry Lake valleys. -Coulston

&&

.DISCUSSION...
/Issued 713 PM MST Tue Feb 4 2025/

 - Meteorological Overview:

A broad, upper level trough will continue to bring snow through
Wednesday. The main axis of moisture has lifted to the North-
Central MT plains, continuing the widespread snow. Moderate to
heavy snow banding will continue on and off throughout the day
across the north-central plains. These moderate to heavy bands
can drop up to an inch of snow per hour at times. Some areas in
Central/Southwest MT will see a lull in snow this
afternoon/tonight until another low pressure system moves east
across the state on Wednesday. This will bring the last "push" of
snow from this system. Convective snow showers/snow squalls will
move across the Southwest Wednesday morning/afternoon. The cold
arctic airmass will linger today through tomorrow morning before
starting to retreat northwards tomorrow afternoon. -Wilson

Behind the Wednesday disturbance, a westerly flow develops across
the region with the cold airmass moderating through Saturday,
through temperatures remain colder than average. Large scale
troughing extending SW from a low in central Canada and upstream
ridging near AK will maintain a cold and unsettled pattern with
additional energy dropping into the trough over BC later this
weekend into next week. While specific details on timing and
moisture remain uncertain, the risk for additional snow and a
return to much colder conditions looks to increase again by early
next week. -Hoenisch

 - Forecast Confidence & Scenarios:

Snow:

The main widespread snow band remains along and north of the
Helena to Hays line. Areas across the southwest and Central MT
will experience lulls in precipitation before another round of
widespread snow arrives Wednesday morning. The cold temperatures
have lowered snow ratios across the region since the dendrites
structures are small/thin. Therefore, I have leaned on the lower
side for additional snow amounts. Most areas across the North-
Central MT plains can expect and additional 1-3". Some areas
could get isolated 4" if they get good periods of moderate to
heavy snow banding. Weak instability in place Wednesday will
allow for convective snow showers/snow squalls to develop across
the Southwest. These will cause quick reductions in visibility
with moderate snow possible.

Cold:

Temperatures have been trending colder than guidance today. I
have expanded the Cold advisory into Toole and Liberty Counties
to account for the colder trends. Temperatures tomorrow morning
will be slightly warmer than this morning. However, wind chills
across the North Central MT plains will range in the teens to low
20s below zero. Areas closer the Continental Divide will see wind
chills of -25 to -35. If overnight temps trend colder, than the
current cold products may be expanded/upgraded further.
-Wilson

&&

.AVIATION...
05/06Z TAF Period

A persistent area of light to moderate snow will continue
mountain-obscuring MVFR/IFR conditions along and north of a line
from KMSO to KHVR, including the KCTB TAF area, through around
18Z. South of this line through Central and Southwest Montana,
VFR conditions will continue through around 08Z, possibly with
some brief periods of mountain top obscuring MVFR conditions in
light snow. After 07Z, a disturbance will spread the mountain-
obscuring MVFR/IFR conditions with similarly light to moderate
snow across the remainder of the forecast area through around 18Z
or so. Conditions are then forecast to gradually improve to VFR
with decreasing snow through 06/00Z.

Regarding winds, the westerly winds aloft associated with the
passing disturbance will cause some mountain wave turbulence, with
the main focus for low-level wind shear staying mostly in the KHLN
TAF area and south through Southwest Montana. Surface winds will
mostly remain light, but gusty southerly winds are forecast to
spread into the KEKS valley area after 09Z. -Coulston

Equipment Note: Observations from the KLWT ASOS resumed being
posted as of 04/2154Z; therefore, AMD NOT SKED has been removed
from the corresponding TAF.

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF -13   8  -7  15 /  80  90   0  10
CTB -17   1 -14  13 / 100  80   0   0
HLN -11  15   4  26 /  60  80  10  10
BZN  -4  20   2  27 /  30  70  10  10
WYS  27  35  -1  24 /  60  90  10  10
DLN  -5  37  10  30 /  40  50   0   0
HVR -11   3 -19   7 /  80  90   0   0
LWT -14  10  -6  20 /  30  60  10  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 11 AM MST Wednesday for Canyon Ferry
Area-Cascade County below 5000ft-Eastern Pondera and Eastern
Teton-Gates of the Mountains-Helena Valley-Meagher County
Valleys-Southern High Plains-Southern Rocky Mountain Front-
Western and Central Chouteau County.

Winter Weather Advisory until 11 AM MST Wednesday for East
Glacier Park Region-Eastern Glacier, Western Toole, and Central
Pondera-Eastern Toole and Liberty-Northern High Plains.

Cold Weather Advisory until 11 AM MST Wednesday for Canyon Ferry
Area-Cascade County below 5000ft-East Glacier Park Region-
Eastern Glacier, Western Toole, and Central Pondera-Eastern
Pondera and Eastern Teton-Eastern Toole and Liberty-Gates of the
Mountains-Helena Valley-Hill County-Northern Blaine County-
Northern High Plains-Southern High Plains-Southern Rocky
Mountain Front-Upper Blackfoot and MacDonald Pass-Western and
Central Chouteau County.

Winter Storm Warning until 5 PM MST Wednesday for Bears Paw
Mountains and Southern Blaine-Big Belt, Bridger and Castle
Mountains-Elkhorn and Boulder Mountains-Gallatin and Madison
County Mountains and Centennial Mountains-Hill County-Little
Belt and Highwood Mountains-Northern Blaine County-Northwest
Beaverhead County-Snowy and Judith Mountains-Upper Blackfoot and
MacDonald Pass.

&&

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