Lewistown, Montana 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

923
FXUS65 KTFX 141721
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1121 AM MDT Sun Jun 14 2026

Aviation Section Updated.

.KEY MESSAGES...

- A warming trend continues through Tuesday, although weak
  passing weather systems may bring a few isolated showers or
  storms for northern areas tonight through early Tuesday.

- Warm and windy conditions develop on Tuesday followed by periods
  of showers and thunderstorms and more gusty winds Tuesday
  evening through Wednesday.

- General unsettled conditions continue for the second half of
  next week with more opportunities for showers and storms.

&&

.DISCUSSION...
/Issued 538 AM MDT Sun Jun 14 2026/

 - Meteorological Overview:

Northwesterly flow aloft generally remains in place through the
end of the workweek. The eastern periphery of a strengthening
Pacific ridge will bring a warming trend over the Northern Rockies
through Tuesday. Although dry conditions generally prevail, there
will be a few weak shortwaves that bring a few isolated showers
or storms, mostly along the Hi-Line tonight through Tuesday.

Westerly flow aloft increases late Monday into Tuesday in advance
of an approaching shortwave and attendant cold front with
H850/H700 winds increasing to the 40 to 50 kt range by Tuesday
evening. This will bring windy and dry conditions Tuesday
afternoon while temperatures surge well into the 80s. A Canadian
cold front moves southward sometime Tuesday evening through early
Wednesday and sends a wave of showers and thunderstorms through
the forecast area, most numerous over central/north-central MT.
CAPE values for this time period look to remain only around a few
hundred J/kg; however, bulk shear will generally be over 40 kts so
there will be at least localized strong wind gusts, some hail,
and downpours with this activity.

Gusty northwesterly winds and scattered shower/thunderstorm
activity linger on the backside of this system through Wednesday
evening and general unsettled conditions continue for the
remainder of the second half of the week. Shower and thunderstorm
activity looks to ramp up again for the weekend with CAPE values
approaching the 1,000 J/kg at times and subtle shortwaves
providing sufficient forcing for stronger convective initiation.
- RCG

 - Forecast Confidence & Scenarios:

Windy conditions and thunderstorms Tuesday and Wednesday...

Westerly winds increase on Tuesday in advance of an approaching
trough and cold front. The NAEFS anomaly index continues to
advertise H700/H500 winds approaching three standard deviations
above climatology. NBM probabilities for 50 mph + gusts continue
to run in the 60 to 80% range along the Rocky Mountain
Front/plains west of I15 Tuesday afternoon, but the swath of
similar probabilities over central and southwest MT have become
more widespread Tuesday evening/night.

The most relevant uncertainties continue to be the timing of the
strongest winds aloft and whether they will move through during
peak diurnal mixing or later in the evening with less momentum
transfer. The Canadian cold front and any pre-frontal northerly
winds shifts will also affect wind magnitude and duration for
northern areas, especially areas along the Northern Rocky Mountain
Front. The timing of showers and thunderstorms will also be
highly dependent on the frontal passage. Thunderstorm hazards,
including localized strong wind gusts, hail, and downpours will be
most widespread over central/north-central MT Tuesday evening,
especially along the Hi- Line.

The winds will shift to a more northwesterly direction on
Wednesday and will generally be strongest over the plains east of
I15, especially along the Hi-Line and over portions of Fergus
County. Showers and thunderstorms will mostly be concentrated over
central/north-central MT again and will generally be weak;
however, they will be capable of transferring the stronger 40 to
50 kt H700 winds to the surface.

The primary impact from these winds and shower/thunder activity
still looks be inclement outdoor recreation and difficult travel
for those operating high profile vehicles. Also, the combination
of temperatures warming well into the 80s and RHs falling to near
critically low levels on Tuesday will also be monitored for fire
weather concerns, although fuels will be less receptive given the
recent rainfall and greenup. Areas that have missed out on the
rainfall, like southwest MT, will be monitored for elevated fire
concerns. - RCG

&&

.AVIATION...
14/18Z TAF Period

VFR conditions prevail through the TAF period. Generally, a few
passing high clouds through the TAF period with calmer winds.
Monday morning, there will be a low end chance for light isolated
showers along the Hi-line, but low confidence in impacting KHVR
resulted in it being left out of the TAF. -Wilson

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  71  45  78  55 /   0   0   0  10
CTB  71  45  78  57 /   0   0  10  30
HLN  73  44  80  55 /   0   0   0  10
BZN  70  39  77  48 /   0   0   0   0
WYS  68  32  75  38 /   0   0   0   0
DLN  69  40  79  48 /   0   0   0   0
HVR  74  46  78  52 /   0  10  20  30
LWT  68  41  71  49 /   0   0  10  20

&&

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

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