Lewistown, Montana Weather Forecast Discussion

806
FXUS65 KTFX 171111
AFDTFX
Area Forecast Discussion
National Weather Service Great Falls MT
511 AM MDT Wed Sep 17 2025
Aviation Section Updated.
.KEY MESSAGES...
- Temperatures warm above to well above normal through the
   remainder of the work week and Saturday.
- Overall light winds and dry conditions are expected through
   Friday.
- Strong and gusty winds are becoming more likely for areas
   along the Rocky Mountain Front on Sunday.
&&
.DISCUSSION...
/Issued 224 AM MDT Wed Sep 17 2025/
- Meteorological Overview:
Upper level ridging was building in over the Northern Rockies this
morning, with clearing skies and light winds helping to support
areas of fog over portions of the Southwest and Central Montana
valleys, especially in areas that recently saw precipitation over
the past 24-36 hours. This fog will slowly dissipate through the mid-
to late morning hours today with increasing solar insolation, but
some localized reductions in visibility below 1 mile are likely
prior to this occurring. Temperatures beneath the aforementioned
upper level ridge will begin to moderate through the remainder of
the work week and into the first half of the weekend, with readings
warming above normal today to well above normal from Thursday
through Saturday. Predominately dry conditions will occur though
this timeframe beneath the ridge, but an isolated shower or storm
can`t be ruled out Friday evening and night as a weak disturbance
moving over Southern Canada begins to flatten the ridge. Light and
variable winds through Friday will begin to increase from the south
and west on Saturday as a cold front approaches, with strong and
gusty winds developing on Sunday as a longwave trough slides east
over Canada and the northern 1/3rd of the CONUS. - Moldan
- Forecast Confidence & Scenarios:
Strong to Potentially High Winds on Sunday :
Confidence is increasing in the first wind event of the 2026 Fall
Season along the Rocky Mountain Front, with climate anomaly
indicators such as the NAEFS and ECMWF EFIs now supporting the
potential for at least a climatologically unusual event here. Latest
NAEFS H850-700 wind speeds from 06z Sunday to 06z Monday are now
progged to increase to between 20-30kts over much of Southwest
through North Central Montana, with 40kts orientated over and
immediately downwind of the Rocky Mountain Front. ECMWF EFIs have
increased to between 0.7 to 0.8 along the Rocky Mountain Front over
this same timeframe with respect to wind gusts, with sustained winds
even ranging from 0.6 to nearly 0.8. NBM probabilities with respect
to wind gusts in excess of 39kts (45 mph) generally range from 30-
60% along and north of the I-90 corridor, with a 70-90% chance along
the Rocky Mountain Front. Furthermore, NBM probabilities for wind
gusts in excess of 48kts (55 mph) and 56kts (65mph) have increased
over the past 24-48hrs along the Rocky Mountain Front, with values
now ranging from a 25-60% chance and 5-30% respectively. Given that
many deciduous trees are either partially or fully leafed out at
this time this wind event has the potential to have some impacts on
otherwise hardy vegetation, with additional impacts expected to
travelers unaccustomed to the winds of the Rocky Mountain Front. -
Moldan
&&
.AVIATION...
17/12Z TAF Period
Primary forecast concern continues to be the potential for LIFR to
MVFR fog through 15-17z this morning at the KLWT, KHLN, KBZN,
KEKS, and KWYS; with latest surface observations and satellite
imagery supporting the development of patchy fog within some of
the valleys of Southwest and Central Montana. Increasing solar
insolation beyond the aforementioned timeframe will help fog to
dissipate and give way to VFR conditions throughout the remainder
of the 1712/1812 TAF period. Mountain obscuration will continue
across portions of Southwest Montana through 18z this afternoon,
with obscuration not expected thereafter. - Moldan
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF  77  46  80  46 /   0   0   0   0
CTB  77  43  77  43 /   0   0   0   0
HLN  77  48  80  49 /   0   0   0   0
BZN  73  42  78  44 /   0   0   0   0
WYS  67  30  71  32 /   0   0   0   0
DLN  70  40  77  42 /   0   0   0   0
HVR  77  46  78  46 /   0   0   0   0
LWT  72  46  75  45 /   0   0   0   0
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
http://www.weather.gov/greatfalls

NWS TFX Office Area Forecast Discussion