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000
FXUS65 KTFX 170238
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
838 PM MDT Tue Apr 16 2024

.SYNOPSIS...

A Canadian cold front will bring periods of snow and gusty northerly
winds tonight into Wednesday, with the heaviest snow over mountain
areas and their adjacent northerly facing foothills. A cold and
moist air mass will then maintain welL below average temperatures
and isolated to scattered snow showers through Friday before more
seasonable temperatures return for the weekend.

&&

.Update...

A strong cold front continues to advance south across Central and
into Southwest Montana as of early this evening, with temperatures
falling 5 to 10 degrees over the course of an hour in its wake.
Additionally, 3hr pressure rises of 2-3mb were leading to strong
and gusty north winds with and following the passage of the front.
Precipitation has been slowly filling in behind the cold front
along the Rocky Mountain Front; however, with dewpoint depressions
of 10 to 20 degrees across most lower elevations across the plains
and valleys of North Central and Central Montana it will likely be
several more hours until the boundary layer saturates and
precipitation makes it to the surface. Further south across
Southwest Montana, snow has been steadily falling across the
Gallatin and Madison Ranges from the late afternoon through early
evening hours associated with a region of mid-level frontogenesis.
Snowfall accumulations of up to 4 inches have been observed near
Big Sky already, with light to at times moderate rain falling
across the Madison and Gallatin Valleys. Given how fast the cold
front has been advancing south this afternoon and evening (faster
than models have been able to resolve so far this evening), I
have lowered temperatures by another 1 to 3 degrees with this
update. Additionally, PoPs have been adjusted to account for
latest radar trends. Otherwise, the remainder of the forecast
remains on track, with precipitation expected to fill in across
most locations beyond midnight tonight as another surge of cold
air advances south. Highest precipitation amounts will continue to
be favored in the mountains and northerly upslope favored
locations of Central and Southwest Montana, especially at the
mid-slopes. - Moldan

&&

.AVIATION...
530 PM MDT Tue Apr 16 2024 (17/00Z TAF Period)

Primary concerns for the TAF period continues to be gusty winds and
snow development tonight. Rain showers have moved into the Bozeman
airfield that should continue periodically through tonight,
transitioning over to a rain and snow mix between 2z and 5z. Gusty
north to northwesterly winds continue through the early evening
hours tonight and concerns for blowing snow tomorrow afternoon for
the Cut Bank airfield will depend on how much snow remains on the
ground after tonight. After 18z, the majority of North Central and
Central Montana airfields conditions should begin to improve and
snowfall diminishes. Mountain obstruction continues through the TAF
period. Webb

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

&&

.PREV DISCUSSION...
/ISSUED 530 PM MDT Tue Apr 16 2024/

Remainder of this afternoon through Friday...Aside from gusty
winds and a few scattered showers this afternoon, the primary
concern will be will be falling temperatures and periods of snow
tonight into Wednesday. Ongoing mid- level cold air advection will
continue, with H700 temperatures between -10 to -15C reaching
Southwest Montana sometime this evening. This will result in
periods snow tonight into Wednesday, heaviest over the
Gallatin/Madison Mountains. There are plenty of uncertainties for
accumulating snow over the lower elevations, but given northerly
flow and the aforementioned H700 temperatures, I felt it necessary
to add a Winter Weather Advisory for the Gallatin valley due to
the accumulating snow potentially impacting the Wednesday morning
peak travel time. Although confidence was too low to add other
lower elevations such as the Dillon area, these areas may also
experience a brief period slushy snow impacts.

Farther north, snow initially develops along the Northern
Continental Divide before spilling southward into the plains via a
secondary cold front. H700 flow will generally favor more of a
northwesterly direction, but will increasing become more northerly
between midnight and 3 am MDT. This will increase snowfall along
the traditional northerly upslope areas along the Central MT
highway 200 corridor during the late overnight hours into
Wednesday morning. There`s little agreement among model guidance,
but the overall pattern favorable for snow and some gusty winds up
to 40 mph in these areas hasn`t changed much over the last 24
hours or so. Similar to the Gallatin valley mentioned above, a
Winter Weather Advisory has been posted for Cascade/Judith Basin
Counties and the Snowy Mountains.

Snow is expected to diminish sometime Wednesday morning for most
locations, but periods of accumulating snow will persist through
the day over the Gallatin/Madison Ranges and cold air advection
will maintain snow shower activity and cold temperatures
elsewhere. Highs will struggle to surpass the middle and upper
30s. The responsible cold trough will remain over the region for
the remainder of the work week, with passing disturbances
continuing the well below average temperatures and isolated to
scattered snow shower activity. - RCG

Saturday through next Tuesday... A broad high pressure ridge is
forecast to move into the western United States during this
period, as a low pressure trough digs south out of the Gulf of
Alaska just off the Pacific coast. This set-up should help warm
temperatures from just below seasonal averages on Saturday to
around 10 degrees above normal by Tuesday. This period should also
remain fairly dry, but weak disturbances ejecting from the
Pacific trough may bring periods of mainly mountain precipitation
and gusty westerly downslope winds. - Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  25  36  23  39 /  80  80  30  20
CTB  21  35  21  36 /  70  50  10  10
HLN  29  37  25  41 /  70  90  20  10
BZN  23  37  17  40 /  90  80  20  10
WYS  20  34   8  37 / 100  90  30  10
DLN  25  36  20  40 /  70  60  20  10
HVR  28  39  24  40 /  20  60  20  20
LWT  23  33  20  35 /  70  70  30  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...

Winter Weather Advisory until 6 AM MDT Wednesday for East
Glacier Park Region-Northern High Plains.

Winter Weather Advisory until noon MDT Wednesday for Big Belt,
Bridger and Castle Mountains-Cascade County below 5000ft-
Gallatin Valley-Gates of the Mountains-Judith Basin County and
Judith Gap-Little Belt and Highwood Mountains-Snowy and Judith
Mountains-Southern High Plains-Southern Rocky Mountain Front-
Upper Blackfoot and MacDonald Pass.

Winter Storm Warning until 6 PM MDT Wednesday for Gallatin and
Madison County Mountains and Centennial Mountains.

&&

$$

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