Helena Valley Northwest, MT 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

941
FXUS65 KTFX 221134
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
434 AM MST Sun Dec 22 2024

Aviation Section Updated.

.KEY MESSAGES...

 - Disturbances passing over North Central, Central, and Southwest
   Montana this week will bring above normal temperatures,
   periods of gusty winds, and continue daily chances of mainly
   mountain precipitation.

 - The strongest winds are forecast to be over the plains today
   and Monday.

 - The period with the best chance for widespread mountain snow,
   and a rain/snow mix at lower elevations, will start Christmas
   Eve day and continue overnight into early Christmas morning,
   likely causing some minor travel impacts.

&&

.DISCUSSION...
/Issued 346 AM MST Sun Dec 22 2024/

 - Meteorological Overview:

Have cancelled the Winter Weather Advisory early this morning for
northern portions of Hill and Blaine Counties. Radar imagery is
indicating that any light freezing precipitation that fell there
overnight has mostly moved out of the area with its associated
shortwave trough. However, slick roads and sidewalks will likely
linger into the mid-morning hours. Light mountain snow and low
elevation rain across portions of Central and Southwest Montana
will also move out of the area.

A progressive westerly flow pattern with a series of passing
disturbances is forecast to remain over the area through at least
next Sunday. This pattern will mostly bring periods of light
mountain snow with chances of a rain/snow mix at lower elevations,
as well as periods of gusty winds. However, the shortwave trough
that is forecast to impact the area the most will move through
Christmas Eve (Tuesday night) into Christmas morning (Wednesday).
Although snow accumulations and impacts are expected to be minor
at this time, the timing of the precipitation coincides with
holiday travel. This weather pattern will also keep temperatures
mostly between 10 and 15 degrees above seasonal averages through
the period.

 - Forecast Confidence & Scenarios:

Regarding winds through the period, confidence is relatively high
that speeds and gusts should remain below High Wind criteria. The
windiest periods as of now are forecast to be early this morning
through early this afternoon and again on Monday. The only area
today with a 50+ percent probability of at least 55 mph wind gusts
(approaching High Wind criteria for most of the area) is along
the Rocky Mountain Front, where criteria is at least 75 mph (and
there is less than a 45 percent probability of that occurring).
Overall probabilities for similar gusts are even lower for Monday
and for the remainder of the week.

Minor snow accumulations are mainly forecast for mountain pass
levels and above, as lower elevation temperatures will mostly
remain warm enough to prevent accumulation of any snow that
falls. 24-hour snowfall amounts have a 50+ percent probability of
exceeding 2 inches with the passage of Monday`s disturbance at and
above mountain pass level in Southwest Montana, which includes
Targhee Pass around West Yellowstone and Lost Trail Pass in
Northwest Beaverhead County. The slightly stronger disturbance
for Christmas Eve lowers snow levels a bit more, spreading
similar probabilities into the Monida Pass and Bozeman Pass
areas, and potentially down to Marias Pass on the Rocky Mountain
Front. The probabilities for amounts greater than 4 inches are
limited to mountain peaks above 7500 feet. As of this time, am not
anticipating needing any winter weather watches or advisories, but
the situation will continue to be evaluated. -Coulston


&&

.AVIATION...
22/12Z TAF Period

Windy conditions will affect the northern Rockies and the Cut Bank
area this morning, while a few rain/snow showers fall along the
divide today. Expect increasing chances for snow on Monday morning
over Southwest MT, with a 30 percent chance of light snow moving
into the Bozeman area by 18z Monday. Mountains/passes will be
obscured at times across CWA through the period. Brusda

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  48  33  51  29 /   0   0  10   0
CTB  44  28  46  22 /  10   0   0   0
HLN  45  29  46  25 /   0  10  30   0
BZN  44  26  44  21 /   0   0  60   0
WYS  31  21  35  15 /  20  40  90  20
DLN  42  26  42  21 /   0  10  30   0
HVR  44  23  46  21 /  10   0   0   0
LWT  45  28  48  25 /  10   0  20   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.

&&

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