799
FXUS65 KTFX 221716
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1016 AM MST Fri Nov 22 2024

Aviation Section Updated.

.KEY MESSAGES...

-Widespread snow and mixed precipitation developing by late this
 morning will bring winter weather impacts to north-central
 Montana through early this evening.

-Snow accumulations of 2 inches or more are expected along the
 US-2 corridor today with amounts of 4 inches or more in the
 Glacier National Park vicinity.

-Lighter snow accumulation but a greater risk for freezing rain or drizzle
 is expected across across southern portions of north-central
 Montana today.

-A second wave of snow will affect north-central Montana on
 Saturday with areas of mixed precipitation possible again across
 some areas.

-A cold front moving across central and southwest Montana Saturday afternoon
 could bring some brief but intense snow showers with gusty
 winds.

&&

.DISCUSSION...
/Issued 444 AM MST Fri Nov 22 2024/

 - Meteorological Overview:

A deep upper level low remains centered offshore of the Pacific
NW with remnants of the atmospheric river of moisture which has
been directed at the west coast spreading northeast across the
Northern Rockies today. Surface high pressure and a colder
airmass is in place across the plains with widespread
precipitation expected to develop along the continental divide
this morning then spreading east across north-central MT this
afternoon as moisture overruns the cooler airmass across the
plains. Deeper cold air across northern portions of North-central
MT will provide better lift with snow accumulations of 2-3 inches
expected today along the Hi-line with higher amounts near the
Rocky Mtn Front and continental divide, including as much as 4-6
inches near Marias Pass. Precipitation type gets more complicated
across southern portions of north-central MT including areas from
Rogers pass east through Great Falls and Lewistown, where the cold
airmass is more shallow and precipitation is lighter but could
mix with freezing rain or drizzle.

Another wave of moisture moves across the region Saturday as the
offshore trough nudges inland with a shortwave disturbance
lifting across the Northern Rockies with an associated area of
surface low pressure and upper level frontal feature shifting
across central  and southwest MT late Saturday afternoon and
evening. Another round of widespread snow is expected across
north-central MT with areas along the Hi-line again favored for
accumulations slightly higher than todays event with some mixed
precipitation also possible again on Saturday across portions of
central MT. Cooling aloft with the upper level features on
Saturday will create a somewhat unstable environment across
central and southwest MT Saturday afternoon with hi-resolution
models suggesting convective snow showers potentially focused
along the frontal feature shifting across SW MT Saturday
afternoon/evening.

 - Forecast Confidence & Scenarios:

Confidence is high in primarily snow impacts along the H-line today
where a Winter Weather Advisory remains in effect through this
evening. Further south across north-central MT, forecast
temperature profiles do support freezing rain, particularly along
the southern edge of the cooler airmass across southern portions
of Cascade county and northern portions of Lewis and Clark county
today. Probabilities for measurable ice accrual are highest
(>50%) along the MT-200 corridor from Great Falls to Rogers Pass,
though overall QPF in these areas is low enough that the risk for
ice accumulation of 0.10" or more is generally less than 20%.

A winter storm watch remains in place for the Rocky Mtn Front and Hi-
line regions Saturday with a winter weather advisory across
adjacent areas to the south across north-central MT. Snowfall
amounts are a bit higher than today`s event but probabilities for
amounts in excess of 4 inches have lowered some with higher
snowfall amounts focused just north of the Canadian border.
Hoenisch

&&

.AVIATION...
22/18Z TAF Period

The initial concern this TAF period will be for a period of snow and
pockets of light freezing drizzle through the afternoon across
Central and North-central Montana. Additional periods of snow and
freezing drizzle will develop this evening and tonight across
similar areas. Further south across Southwest Montana, the main
concern will be for a breezy southerly wind through north south
oriented valleys, with just a low-end chance for rain today and
tonight. Mountains will be obscured from low clouds and
precipitation through much of the TAF period across northern areas.
-AM

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  26  20  32   9 /  90  80  90  50
CTB  20  13  22   2 /  90  90  90  60
HLN  39  28  45  18 /  60  70  90  50
BZN  49  28  48  18 /  30  40  80  70
WYS  41  18  36  14 /  20  50 100  90
DLN  47  31  44  18 /  20  50  80  40
HVR  27  17  29   6 / 100 100 100  50
LWT  33  20  44   9 /  60  60  80  60

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 11 PM MST this evening for Bears
Paw Mountains and Southern Blaine-Cascade County below 5000ft-
East Glacier Park Region-Eastern Glacier, Western Toole, and
Central Pondera-Eastern Pondera and Eastern Teton-Eastern Toole
and Liberty-Fergus County below 4500ft-Gates of the Mountains-
Helena Valley-Hill County-Judith Basin County and Judith Gap-
Little Belt and Highwood Mountains-Northern Blaine County-
Northern High Plains-Snowy and Judith Mountains-Southern High
Plains-Southern Rocky Mountain Front-Upper Blackfoot and
MacDonald Pass-Western and Central Chouteau County.

Winter Weather Advisory from 5 AM Saturday to 5 AM MST Sunday
for Cascade County below 5000ft-Eastern Pondera and Eastern
Teton-Western and Central Chouteau County.

Winter Storm Watch from late tonight through late Saturday night
for East Glacier Park Region-Southern Rocky Mountain Front.

Winter Storm Watch from late tonight through late Saturday night
for Bears Paw Mountains and Southern Blaine-Eastern Glacier,
Western Toole, and Central Pondera-Eastern Toole and Liberty-
Hill County-Northern Blaine County-Northern High Plains-Southern
High Plains.

&&

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