Severe Thunderstorm Warning 73, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
Issued by National Weather Service Missoula MT
611 PM MDT Fri Jul 17 2026

Aviation Section Updated.

.KEY MESSAGES...

 - Scattered to numerous showers and thunderstorms will move in a
   southwest to northeast fashion later this afternoon through the
   early overnight hours.

 - Thunderstorm hazards will include strong, gusty winds, hail,
   and torrential downpours capable of localized flooding.

 - Warmer temperatures and slightly drier conditions move in for
   the weekend, although there will still be widely scattered
   shower and thunderstorm activity.

&&

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

A shortwave embedded within a southwesterly flow aloft will
interact with monsoon moisture and an unstable profile for the
development of clusters to broken lines of thunderstorms moving
in a southwest to northeast fashion this afternoon into tonight.
The most robust CAPE over 1,500 J/kg will be slightly farther east
of the 30 +kt bulk shear area, but there will certainly enough
overlap for at least scattered strong to severe thunderstorms.
Additionally, anomalously high PWATS, generally between an inch
and an inch and a half, will be capable of producing brief periods
with rainfall rates in the half to one inch range and even higher
in the stronger cores. A flash flood watch was sent out again for
the Horse Gulch Burn scar for this afternoon and evening. Urban
areas that receive these heavier rainfall rates will also be
susceptible to localized flooding, especially over central and
north-central MT, though confidence was not quite high enough for
additional flood products at this time.

Slightly drier air moves in for the weekend as the flow aloft
becomes more westerly and pushes the richest moisture off to the
east. There will be another shortwave that passes through again
on Saturday, but it will have less CAPE and moisture to interact
with. The widely scattered showers and storms that do develop
will contain gusty, to locally strong winds with RH's dropping
back down to the teens Saturday afternoon. Similar conditions
prevail for Sunday, though storm coverage may be even less than
Saturday.

Aside from a brief cooldown on Monday thanks to a passing cold
front, temperatures will be on the rise thanks to high pressure
aloft building over the Great Basin area. The Northern Rockies
will still be far enough north for shortwaves and moisture to
compromise the high and bring at least widely scattered shower and
thunderstorm activity. - RCG

&&

.AVIATION...
18/00Z TAF Period

Showers remain in the area with thunderstorms lingering over the
Lewis Range and pushing eastward. Easterly winds at the surface
from KGTF eastward this evening will shift to west southwest as
the frontal boundary moves through. Expect showers and
thunderstorms to push to the north northeast. Showers and
thunderstorms will be the most widespread until around 06Z Sun
when high resolution models show them becoming more scattered and
dissipating to the north. Radar shows some gusty outflow
boundaries stemming from the bulk of the storms which may impact
areas around KGTF and KHLN through 02Z Sat. Temporary strong
northwest winds possible with these storms. Overnight, skies will
clear slowly which will increase radiational cooling. Areas that
received rain and then clear will see some patchy fog, but
widespread dense fog is less of a concern this evening. There is
around a 10-15% chance of IFR CIGs around KCTB from 08Z-14Z Sat,
which is one area that models are highlighting. A return of
showery conditions is possible after 20Z Sat, but not expected to
be as widespread as this evening.      -Muessle

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  95  61  95  61 /  20  90  10  20
CTB  90  60  91  57 /  30  70  10   0
HLN  94  62  93  61 /  50  70  30  30
BZN  93  57  92  57 /  30  70  20  20
WYS  85  48  87  48 /  50  80  20  10
DLN  88  55  89  55 /  70  70  20  10
HVR  98  64  97  63 /   0  70  20  20
LWT  90  56  89  57 /  10  60  20  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch until midnight MDT tonight for Big Belt,
Bridger and Castle Mountains.

&&

http://www.weather.gov/greatfalls

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Preliminary Local Storm Report
National Weather Service Great Falls MT
700 PM MDT Fri Jul 17 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0650 PM     Tstm Wnd Gst     7 SSE Ulm               47.33N 111.48W
07/17/2026  M56 MPH          Cascade            MT   Trained Spotter

&&

JTG

Special Weather Statement
National Weather Service Great Falls MT
708 PM MDT Fri Jul 17 2026

MTZ319-320-322-323-180200-
Helena Valley MT-Elkhorn and Boulder Mountains MT-
Big Belt, Bridger and Castle Mountains MT-Canyon Ferry Area MT-
708 PM MDT Fri Jul 17 2026

...A STRONG THUNDERSTORM WILL IMPACT SOUTHEASTERN LEWIS AND CLARK...
NORTHWESTERN BROADWATER AND NORTHEASTERN JEFFERSON COUNTIES THROUGH
800 PM MDT...

At 707 PM MDT, Doppler radar was tracking a strong thunderstorm near
Townsend, moving northwest at 25 mph.

HAZARD...Wind gusts up to 50 mph and nickel size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor hail damage to vegetation is
         possible.

Locations impacted include...
Townsend, Silos, Winston, and Goose Bay.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 4637 11126 4626 11146 4652 11189 4668 11159
TIME...MOT...LOC 0107Z 138DEG 20KT 4638 11145

MAX HAIL SIZE...0.88 IN
MAX WIND GUST...50 MPH

Glinskas