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201
FXUS65 KTFX 301009
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
409 AM MDT Tue Apr 30 2024

.SYNOPSIS...

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A slow moving Pacific storm system will bring breezy to windy
conditions, below average temperatures and periods of rain and
snow through much of this week with more widespread precipitation
and periods of wintry conditions across portions of north-
central and central Montana Wednesday through Thursday.
Temperatures moderate some heading towards the weekend, but the
typically active spring weather pattern will persist for the
foreseeable future.
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&&

.DISCUSSION...

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Satellite imagery this morning reveals a complex upper level low
taking shape over SW Canada with several notable shortwaves pivoting
around it, including a stronger wave approaching the Pacific NW
and weaker waves lifting out of the Northern Rockies and MT along
the International Border. While we spend most of today in between
these disturbances, cold/unstable westerly flow aloft and the
arrival of additional moisture ahead of the disturbance moving
into the Pacific NW will support the development of showers this
afternoon, across the western and southwest MT mountains. Areas
near Glacier NP will also see an increase in snow showers this
afternoon as one of the embedded disturbances within the larger
scale low moves east along the MT/AB border. Otherwise, breezy to
windy and cooler conditions will be noticeable with afternoon
temperatures around 10 degrees below seasonal averages and
westerly winds with gusts 30-40 mph. Highest winds speeds today
will be near the Rocky Mtn Front and central MT mountain ranges
where a few gusts may exceed 45 mph, particularly for a period
late this morning through mid-day with the passage of an embedded
wind maximum.

The larger scale closed upper level low moves east of the Rockies
tonight with its circulation shifting slowly across MT/AB/SK
through Thursday. Models are in general agreement and continue to
trend somewhat slower with the arrival of more widespread
precipitation circulating into the forecast area. Widespread
precipitation develops across southern AB/SK in association with a
TROWAL (trough of warm air aloft) and shifts southwest into areas
along the east side of Glacier NP by Wednesday morning. Colder
air aloft wraps into the circulation Wednesday with widespread
precipitation expanding south and east across much of north-
central MT by Wednesday afternoon with moist/cyclonic NW flow now
forecast to linger across the area through at least Thursday
afternoon. This has shifted the more impactful period of winter
precipitation for portions of central MT to late Wednesday through
Thursday, though precipitation amounts have not changed significantly.

Winter storm warnings and advisories for The Glacier NP/Rocky Mtn
Front vicinity begin at midnight tonight with areas near the AB
border being initially impacted tonight before precipitation
spreads south on Wednesday. Winter weather advisories were added
for the Big Belt/Bridger and Snowy mountain ranges beginning
Wednesday afternoon with the Winter Storm Watch for the Little
Belts continuing while these highlights were extended through
Thursday afternoon. There is some potential for additional winter
weather highlights across portions of central MT adjacent to the
Little Belts but considerable uncertainty exists at these lower
elevations due to marginal temperatures with melting and
compaction likely to limit accumulation and impacts to roads.
Still, the later onset of precipitation towards Wednesday night
and Thursday could allow for some overnight accumulation and minor
winter weather impacts to the Thursday morning commute that will
need to be watched.

Models continue to delay the exit of troughing from the area
through Friday though the bulk of the widespread precipitation
should be ending Thursday night. A brief period of ridging is
possible early this weekend before the next round of troughing
arrives late this weekend into early next week with models
suggesting temperatures remaining closer to seasonal averages for
this period. Hoenisch
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&&

.AVIATION...
1210 AM MDT Tue Apr 30 2024 (30/06Z TAF Period)

North-central Montana (KCTB, KHVR): KCTB will stay dry through the
first 6 hours of the TAF period while rain showers linger around the
vicinity of KHVR as moisture continues to push to the east. After a
brief lull in activity, another disturbance moving through this
afternoon will bring more precipitation across the hi-line after
30/18Z. A rain/snow mix is possible for KCTB while further east at
KHVR temperatures will be warm enough for rain through the entire
TAF period. Gusty winds up to 40kts for KCTB and 30kts for KHVR will
be possible through most of the TAF period. Rain and snow combined
with gusty winds may work to bring temporary periods of MVFR/IFR
conditions to both north-central Montana terminals.

Central Montana (KGTF, KHLN, KLWT): Periods of MVFR/IFR will
continue at KLWT through 30/09Z before the rain moves out of the
area to the east. Otherwise, VFR are expected to prevail at all
three central Montana sites through the TAF period. There is a
chance for mixed precipitation at KHLN between 30/17Z and 30/21Z but
otherwise all three terminals are expected to remain dry through the
TAF period with gusty winds up to 32kts possible during the daytime
hours.

Southwest Montana (KBZN, KEKS): Snow showers will slowly taper off
by 30/12Z across southwestern Montana with a roughly 6 hour lull
before another round of precipitation returns to the area and
remains through the rest of the TAF period. During the day,
predominately rain is expected with winds gusting up to 26kts. The
transition to snow is expected to start after 30/22Z, becoming
predominately snow after 01/03Z. Periods of MVFR and mountain
obscuration are possible across the region after 30/18Z.

-thor

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

&&

.PRELIMINARY POINT TEMPS/POPS...
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GTF  51  31  47  32 /  20  30  70  80
CTB  47  31  43  32 /  50  50  80  80
HLN  51  31  50  36 /  30  10  60  60
BZN  49  24  48  29 /  40  40  40  40
WYS  42  20  40  19 /  60  70  60  30
DLN  47  24  45  28 /  30  30  30  20
HVR  54  32  50  33 /  30  40  70  70
LWT  48  27  46  28 /  10  10  60  60
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&&

.TFX WATCHES/WARNINGS/ADVISORIES...
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Winter Storm Warning from midnight tonight to noon MDT Thursday
for East Glacier Park Region.

Winter Weather Advisory from midnight tonight to noon MDT
Thursday for Northern High Plains-Southern Rocky Mountain Front.

Winter Storm Watch from Wednesday morning through Thursday
afternoon for Little Belt and Highwood Mountains.

Winter Weather Advisory from noon Wednesday to 6 PM MDT Thursday
for Big Belt, Bridger and Castle Mountains-Snowy and Judith
Mountains.
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&&

$$

http://www.weather.gov/greatfalls