385
FXUS65 KTFX 230006
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
506 PM MST Fri Nov 22 2024

Aviation Section Updated.

.KEY MESSAGES...

-Snow and or mixed precipitation will continue to impacts to
 Central and North- central Montana through this evening.

-A second wave of snow will affect north-central Montana on
 Saturday with areas of mixed precipitation changing back to all
 snow by Saturday afternoon and evening.

-Saturday afternoon and evening northerly winds behind the cold
 front may gust up to around 40 mph at times and cause short
 periods of localized blizzard conditions along the Northern
 Rocky Mountain Front and the the western portions of the Hi-Line.


-The cold front will also bring some brief but intense snow
 showers with gusty winds to Southwest Montana Saturday afternoon
 and evening.

&&

.DISCUSSION...
/Issued 225 PM MST Fri Nov 22 2024/

The primary concerns for this evening and tonight will be
continued light snow and or mixed precipitation for Central and
North- central MT. Any road surfaces that may be wet this
afternoon are expected to refreeze and become slick again once
diurnal heating wanes.

Then attention turns to Saturday and Saturday night when a cold
cold front will bring gusty northerly winds and accumulating snow
to Central/North-central MT, with the worst condtions expected
along the Rocky Mountain Front and the western portions of the Hi-
Line where a potential barrier jet increases the chances for wind
gusts over 40 mph to around 30% Saturday afternoon and evening. I
considered placing this area under a blizzard warning, but opted
to upgrade the winter storm watch to a winter storm warning due
to lack of confidence in longer term blizzard impacts. Otherwise,
The remaining portion of the winter storm watch was upgraded to a
winter weather advisory. Southwest MT will also be impacted by the
cold front, though slightly warmer temperatures look reduce the
overall impacts. No winter weather products were sent out for this
forecast package. These situations will continue to be monitored
going forward.

Please see the still relevant previous discussion for details
about the longer term. - RCG

 - 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...
23/00Z TAF Period

Varying conditions are expected over the next 24 hours as one
system exits the area and the next one begins to push in. Expect
low cigs and vis due to SN and areas of FZRA to gradually improve
from west to east over the next few hours (through 6z or so).
After a lull overnight, another round of RA and SN will push in
from the west, bringing another round of IFR conditions due to
falling and blowing snow. Ludwig

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  20  32   9  18 /  70  90  70  30
CTB  13  22   3  13 /  70  90  50  30
HLN  28  45  18  33 /  70  80  70  30
BZN  29  48  18  34 /  40  70  80  40
WYS  19  36  16  31 /  20  90  90  70
DLN  31  44  19  34 /  50  70  60  20
HVR  17  29   5  18 /  70  90  50  20
LWT  20  44   9  21 /  50  60  70  50

&&

.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 Bears Paw Mountains and Southern Blaine-Cascade County below
5000ft-Eastern Pondera and Eastern Teton-Hill County-Northern
Blaine County-Southern High Plains-Western and Central Chouteau
County.

Winter Storm Warning from 2 AM Saturday to 5 AM MST Sunday for
East Glacier Park Region.

Winter Storm Watch from late tonight through late Saturday night
for Bears Paw Mountains and Southern Blaine-Hill County-Northern
Blaine County-Southern High Plains.

Winter Weather Advisory from 2 AM Saturday to 5 AM MST Sunday
for Southern Rocky Mountain Front.

Winter Storm Watch from 2 AM MST Saturday through late Saturday
night for Southern Rocky Mountain Front.

Winter Storm Warning from 5 AM Saturday to 5 AM MST Sunday for
Eastern Glacier, Western Toole, and Central Pondera-Eastern
Toole and Liberty-Northern High Plains.

&&

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