Lewistown, Montana 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

747
FXUS65 KTFX 052320
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
Issued by National Weather Service Missoula MT
520 PM MDT Fri Sep 5 2025

Aviation Section Updated.

.KEY MESSAGES...

- Dry conditions are expected for most locations through the
  weekend with temperatures warming up to around 10 degrees above
  average by Sunday.

- Isolated shower and thunderstorm activity will slowly increase
  over the southwest and along the Continental Divide this
  weekend.

- Monsoon moisture increases areawide next week and brings daily
  rounds of widely scattered showers and thunderstorms for much of
  the workweek.


&&

.DISCUSSION...
/Issued Issued by National Weather Service Missoula MT/

 - Meteorological Overview:

Ridging aloft will bring mostly dry conditions and warming temperatures
through the weekend; however, another night with low temperatures dipping
into the 30s is expected within the cold prone valleys in Southwest
Montana and over the plains of Central and North Central Montana
tonight. Troughing over the Pacific Northwest will begin to
flatten the ridge some this weekend while moisture and weak
disturbances begin to encroach the Northern Rockies. The main impact
from this will be a day to day increase in isolated shower and
thunderstorm/lightning activity over the dry southwest, mostly on
Sunday.

Ensembles favor the Pacific Northwest trough deepening and
sending additional moisture into the region early next week via a
high amplitude southerly flow aloft. Afternoon temperatures will
warm to around 10 to 15 degrees above average through the mid-
week period while daily rounds of widely scattered shower and
thunderstorm activity increasing areawide with the added moisture
and instability. - RCG/Moldan

 - Forecast Confidence & Scenarios:

Frost and Freeze Potential Tonight...

Those with sensitive vegetation across portions of the valleys and
plains of North Central through Southwest Montana should consider
taking precautionary measures as clear skies and light winds
across the region will favor ideal radiational cooling processes
during the overnight hours tonight. Latest NBM probabilities
support a 20-40% chance for low temperatures to fall to or below
36 degrees along and northwest of the US Hwy 87 corridor from
Great Falls to Havre and generally east of the I-15 corridor from
Great Falls to Shelby. NBM probabilities for the cold prone Big
Hole and Hebgen/West Yellowstone Valleys generally range between a
40-60% chance for low temperatures to fall to or below 32 degrees
tonight.
- Moldan

Shower and thunderstorm activity increasing this weekend into
next week...

Monsoon moisture slowly returns to the Northern Rockies this
weekend into next week. Isolated shower and thunderstorm activity
will initially impact southwestern areas south of I90 Saturday
afternoon and night. The primary concern will be for some storms
offering lightning but little rainfall given dry surface
conditions. Shower and thunderstorm activity expands north and
eastward on Sunday, but Southwest Montana and areas along the
Continental Divide will see the most activity. There will be more
productive storms on Sunday, but higher CAPE in the 500 to 1,000
J/kg range will be capable of producing more lightning than on
Saturday. Additionally, some storms may still be on the dry side
with strong erratic wind gusts due to minimum RHs in the 20s and
lower in some cases.

Deeper southerly flow will bring periods of widely scattered
showers and thunderstorms to all areas Monday through Wednesday.
Precipitable water values nearing the 0.75 to 1.0 inch mark
combined with afternoon instability and forcing from the trough
may be sufficient for the development of a few stronger storms
Tuesday into Wednesday with gusty winds, brief downpours, and some
hail in addition to lightning. Cooler, breezy, and showery
conditions are expected towards the end of the workweek behind the
weakening and departing trough. - RCG

&&

.AVIATION...
06/00Z TAF Period

The primary concern this TAF period will be for instances of
reduced surface and slant-range visibility due to wildfire smoke,
primarily across Southwest Montana. VFR conditions prevail
otherwise with light winds forecast through the TAF period. -AM

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  43  81  49  85 /   0   0   0  10
CTB  40  78  45  83 /   0   0   0   0
HLN  47  84  55  85 /   0   0   0  10
BZN  42  84  50  84 /   0   0   0  20
WYS  33  77  42  73 /   0   0  10  50
DLN  45  82  50  80 /   0  10  10  20
HVR  38  77  45  82 /   0   0   0   0
LWT  40  77  48  81 /   0   0   0  10

&&

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

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