Lewistown, Montana 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

872
FXUS65 KTFX 191505
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
905 AM MDT Sat Jul 19 2025

.KEY MESSAGES...

- Isolated showers and thunderstorms along the Hi line Saturday
  afternoon.

- A wetter and cooler start to next week across North-Central MT.

- Above temperatures towards end of next week.

&&

.UPDATE...

Morning update has been published, with the main adjustment being
to increase the areal coverage of slight chance (i.e. 15-24%) PoPs
across North Central and Central Montana to account for shower
activity that was being supported by warm air advection processes
this morning. Otherwise the remainder of the forecast remains on
track, with a Marginal Risk for severe thunderstorms this
afternoon across far eastern portions of Blaine and Fergus
Counties, generally along and east of a Turner, to Hays, to Grass
Range line. - Moldan

&&

.DISCUSSION...
/Issued 524 AM MDT Sat Jul 19 2025/

 - Meteorological Overview:

A front and lingering instability has kept isolated showers and
thunderstorms in Central MT early this morning. These showers and
storms are expected to wind down over the next few hours. This
front will also keep low end chances for an isolated shower or two
along the Hi-Line this morning. An upper level trough will pass
through the weekend as it digs south out of Canada. This with a
weak shortwave moving through will bring isolated showers and
thunderstorms along the Hi-line Saturday afternoon. Current
placement of this shortwave keeps most activity in Canada and
Eastern Montana, but can`t rule out a few showers and storms to
clip the Montana/Canadian border and Fergus Co. The upper level
trough continues to dig Sunday, which will have the slight
potential to develop afternoon showers and thunderstorms across
the region. There remains uncertainty in the strength of
thunderstorms with weak CAPE, but an increase in moisture and
forcing aloft will introduce slight chances for precipitation.

This troughing pattern continues into next week. A weather system
will bring the next chances for widespread rain across North-
Central MT Monday and Tuesday. Temperatures will also fall back
below normal. This troughing pattern looks to stay through mid
week, which ensembles are unclear on how long to keep this
pattern. Some ensembles keep the southwesterly flow aloft through
the weekend, while some keep it more of a zonal flow pattern.
Temperatures look to trend back above average by the end of next
week.

 - Forecast Confidence & Scenarios:

Hi-res guidance has been pretty consistent in keeping showers and
thunderstorms this afternoon confined to the Hi-line and eastern
Fergus Co. Stronger thunderstorms should stay off to the east, but
I can`t rule out getting clipped by one or two. Sunday remains a
question mark on convection. There is an increase in moisture and
shear with the upper-levle wave. However, CAPE is limited, which
decreases chances for stronger storms. If CAPE increases, then we
will have to watch for a few strong storms. Monday is a similar
story, with models keeping CAPE limited but with good shear and
moisture. Thunderstorm chances can also trend higher if CAPE
increases.

For precipitation amounts Monday and Tuesday, there`s a 50-80%
chance for 0.1" of rain in North-Central MT and a 40-60% chance
for 0.25". Not much precipitation is expected in Southwest MT.

There remains uncertainty in how dry the later part of the weak
remains. It`ll mainly depend on how long the southwest flow aloft
pattern, with some models hint at precipitation lasting through
Friday with this pattern and keep the weekend dry. Some ensembles
that keep the southwest flow aloft pattern through next weekend,
which will introduce low end chances for precipitation then.
-Wilson

&&

.AVIATION...
19/12Z TAF Period.

A few scattered showers/thunderstorms are currently affecting the
eastern portions of North Central MT. This activity should
diminish by 16z. However expect another round of new storms near
the Canadian border to become more widespread by 20z, possibly
affecting areas as far south as Lewistown by late afternoon. Some
smoke could affect Southwest MT form wildfires in the panhandle of
ID. Other than breezy afternoon winds, expect VFR conditions to
prevail outside of any shower/thunderstorm/fire activity. Brusda

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  84  55  81  56 /  10  10  10  10
CTB  75  49  75  52 /  20  20  20  20
HLN  85  57  82  56 /  10  10  20  10
BZN  88  50  87  51 /  10  10  20  20
WYS  79  39  79  43 /  20   0  20  10
DLN  84  49  83  50 /   0   0  20   0
HVR  85  54  82  54 /  30  20  10  20
LWT  81  52  77  52 /  20  20  30  30

&&

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

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