Lewistown, Montana 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

210
FXUS65 KTFX 040424
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
924 PM MST Tue Dec 3 2024

Aviation Section Updated.

.KEY MESSAGES...

 - Slightly cooler temperatures on Wednesday over the plains in
   wake of a weak cold front, with below normal temperatures
   linger in the Milk and Missouri River Valleys on Thursday.

 - High temperatures on Saturday will be 10 to 20 degrees above
   normal across all of Southwest through North Central Montana.

 - Predominately dry conditions are expected through the
   remainder of the work week; however a few light rain/snow
   showers can`t be ruled out on Wednesday across Hill and Blaine
   Counties.

 - Wind begin to increase from Thursday through Friday along the
   Rocky Mountain Front, peaking over the weekend.

 - Better chances for widespread precipitation return this
   weekend.

&&

.UPDATE...
/Issued 843 PM MST Tue Dec 3 2024/

Satellite imagery this evening shows high clouds streaming across
north-central and southwest MT in northwest flow aloft downstream
of an upper level ridge centered across the Pacific NW. At the
surface, winds are relatively light across most of the area with
the exception of locations along the immediate east slopes of the
Rocky Mtn Front. With primarily thin cloud-cover, cannot rule out
some patchy fog development across portions of mainly Hill, Blaine
and Chouteau counties while quiet conditions prevail otherwise
through tonight. Hoenisch

&&

.DISCUSSION...
/Issued 843 PM MST Tue Dec 3 2024/

 - Meteorological Overview:

H500 ridging over the western seaboard will gradually shift
eastward towards the Northern Rockies, with the ridge axis moving
over the region on Friday. As the ridge shifts eastward several
weak shortwaves will crest the ridge and dive southeast and over
the Northern Rockies. These shortwaves will be largely robbed of
moisture and predominately lead to periods of increased cloud
cover; however, and isolated rain/snow shower can`t be ruled out
over extreme northeastern portions of North Central Montana (i.e.
northeast of a Lewistown to Chester line) on Wednesday and then
over the Continental Divide on Friday. By Saturday a potent
shortwave over the Gulf of Alaska will breakdown the H500 ridge
over the Western CONUS/Canada, with this shortwave moving over
the Northern Rockies during the day on Sunday and northerly flow
remaining in place over the region through early next work week.
The breakdown of the ridge will lead to a period, potentially
24-36 hours, of strong to High Winds, especially along the Rocky
Mountain Front. Additionally, this shortwave will bring
increasing chances for widespread precipitation to most of
Southwest through North Central Montana, with the best chances
occurring in the mountains. - Moldan

 - Forecast Confidence & Scenarios:

Winds :

Although breezy conditions are generally expected for much of the
week, the strongest and most widespread winds hold off until the
weekend. Winds initially strengthen again along the Rocky
Mountain Front Thursday night amid a tightening pressure gradient
for more of a `run of the mill` event before the potentially
higher impact winds move in late Friday through early Sunday.
Around 55% of the (values in parenthesis) ensembles now favor a
vigorous trough diving into the Northern Rockies this weekend,
though there are slight timing differences among the supporting
members. Climate anomaly indicators such as the NAEFS and the EC
EFI are now picking up a signal for a stronger end wind event,
with NAEFS H850-700 wind speeds now forecasted to approach 2
standard deviations above normal and EFI value of 0.5 to 0.7, and
even a shift of tails of 0, residing along and in lee of the
Continental Divide. NBM probabilities for wind gusts in excess of
55 mph continue to increase from late Friday through Saturday,
with areas like Cut Bank, Browning, and East Glacier now
possessing a 50% and 80%, 80% and 90%, and 70% and 90% chance
respectively. - RCG/Moldan

Snow this weekend into Monday:

More seasonable temperatures and accumulating snow potential are
expected to follow the winds Sunday into Monday. Most ensemble
members continue to forecast H700 temperatures potentially
falling to around -15C Sunday night into early Monday for at
least some light snow at all elevations, particularly the
northerly upslope areas Central/North-central and Southwest MT.
Overall, mountain areas are favored for the higher amounts. Of
course this will all depend on the 55% chance that the trough
will be deep and cold enough to materialize this scenario.

Temperatures :

Temperatures will overall be warming well above average through
Saturday, though the colder air will linger in the river valleys
of Hill, Blaine, and Chouteau counties through Thursday. I
lowered temperatures toward the Canadian models in these areas to
account for slow warming today and the cold front moving in later
today into Wednesday. - RCG

&&

.AVIATION...
04/06Z TAF Period

VFR conditions prevail at area terminals through tonight under a
northwest flow aloft with some thin high level clouds streaming
across the region. Surface winds will remain somewhat variable
across the plains overnight with a wind shift to the north and
northeast moving south across the N-central MT plains Wednesday
morning. Low clouds are likely to spread south into the KHVR and
KCTB areas with the wind shift Wednesday morning with potential
for a period of MVFR ceilings. Hoenisch

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  22  40  19  48 /   0   0   0   0
CTB  17  31  19  40 /   0   0   0   0
HLN  26  46  23  48 /   0   0   0   0
BZN  21  46  18  47 /   0   0   0   0
WYS   8  38   6  38 /   0   0   0   0
DLN  23  46  18  45 /   0   0   0   0
HVR  14  26  11  33 /   0  10  10   0
LWT  25  42  22  50 /   0  10   0   0

&&

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

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