Severe Thunderstorm Warning 10, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
527 PM MDT Tue May 26 2026

Aviation Section Updated.

.KEY MESSAGES...

- Very warm to hot temperatures continue for much of the
  workweek,especially over the plains.

- There will also be daily rounds of showers and thunderstorms,
  some will be strong to severe and may contain localized heavy
  downpours.

- Cooler temperatures and an opportunity for more widespread
  precipitation moves in this weekend.

&&

.DISCUSSION...
/Issued 139 PM MDT Tue May 26 2026/

 - Meteorological Overview:

A blocking pattern will maintain troughing over the western conus
for the next week or so, with a mid -level closed low drifting
southeastward from the Pacific NW into the Great Basin and
remaining there through the workweek. This will bring in an
increasingly unstable south to southeasterly flow aloft over the
Northern Rockies for daily rounds of showers and thunderstorms. A
shortwave will provide bulk shear over 30 kts today while ML CAPE
stays mostly in the 200 to 600 J/kg range, highest along the Rocky
Mountain Front. The primary threat for this afternoon and evening
will be localized gusty winds with inverted V forecast soundings,
but some instances of near or severe hail can't be ruled out with
H500 temperatures as low as -15C.

The flow aloft becomes weakly diffluent on Wednesday and Thursday
and shear levels drop to negligible levels due to a general lack
of shortwave energy; however, ML CAPE ramps up to over 1000 J/kg
and PWATS begin to approach and even exceed the one inch mark,
highest over central and north-central MT. The lack of forcing
will result in lower storm coverage away from terrain, but
localized downpours will become a concern in addition to a
continued wind and hail threat.

The closed low and associated elongated trough over the Pacific
NW will undergo some shearing and transformation before it swings
northward into the Northern Rockies heading towards the weekend.
This looks to bring a round of stronger to severe thunderstorms
sometime between late Thursday through early Saturday; followed by
a period of cooling temperatures and more widespread areas of
rain and embedded thunderstorms later Saturday into Sunday. A
southwesterly flow aloft then develops in the wake of the
departing system and brings warming temperatures and more rounds
of showers and thunderstorms next week. - RCG

 - Forecast Confidence & Scenarios:

Daily rounds of showers and thunderstorms though Friday followed
by more widespread precipitation this weekend...

Showers are already lifting northward into western and
southwestern MT early this afternoon. Cloud cover is hampering
CAPE and DCAPE over the southwest, but this should change as this
activity moves over the warm and dry surface farther north.
Forecast soundings indicate that strong wind gusts will be the
primary hazard to deal with and this is corroborated by the latest
suite of hires guidance. Convective wind gusts will generally
range somewhere between 35 and 60 mph, strongest along the Rocky
Mountain Front and over central/north-central MT, especially along
and southwest of a Sweetgrass Hills to Lewistown line. Storm
motion will be south/southeast to north/northwest, a little
different than the typical southwest to northeast motion we
typically see. This added easterly component may also increase the
risk for an isolated land spout, although the chances for such an
event are less than 2% within 25 miles of any point. The
strongest and most widespread shower and thunderstorm activity
will generally occur between 3 and 9 pm tonight, with a more
isolated brand of showers continuing into the overnight hours.

The wind shear necessary for the maintenance of stronger showers
and thunderstorms drops off on Wednesday and Thursday with lack of
shortwave energy and the forcing from the main low still far to
our southwest. Some of this void will be fulfilled by ML CAPE
levels increasing to over 1000 J/kg and PWATs nearing the one inch
mark, but storm coverage should generally be slightly less than
today for areas away from higher terrain. The slower storm motion
and higher moisture levels will increase the concern for localized
flooding for higher prone areas such as burn scars, especially
for mountain areas and lower elevations west of I15. There will
also be continued instances of thunderstorm winds and hail.

Most ensembles keep the main closed low pressure system over the
Great Basin area through the workweek before swinging back
northward towards the Northern Rockies this weekend. If this pans
out as forecast, there will be a period of stronger thunderstorms
sometime between late Thursday and early Saturday followed by more
widespread rains and embedded thunderstorms for the second half
of the weekend. Although, there are some uncertainties to iron
out, the heaviest precipitation is projected to occur along the
Continental Divide and over central and southwest areas extending
from the highway 12 corridor northward to the central island
ranges. The latest NBM probabilistic guidance currently gives a 50
to 70% chance for rainfall amounts exceeding one inch for the 48
hour period ending 6 am Monday morning. - RCG

&&

.AVIATION...
26/18Z TAF Period

Predominately VFR conditions are expected through the 2700/2800
TAF period; however, temporary MVFR/low-VFR conditions are
possible beneath shower and thunderstorm activity. Biggest impact
to terminal operations will be gusty and erratic winds up to
45kts beneath and near thunderstorm activity across the KWYS,
KEKS, KBZN, and KHLN through 03z this evening and 02-07z Wednesday
at KGTF, KCTB and KLWT. Mountains will be obscured at times over
the next 24 hours. - Moldan

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  55  85  56  91 /  70  30  30  20
CTB  54  82  52  88 /  70  50  50  30
HLN  51  84  52  90 /  70  40  30  20
BZN  45  83  46  90 /  50  40  20  20
WYS  37  79  39  83 /  50  40  10  20
DLN  43  79  46  87 /  50  30  20  20
HVR  61  95  55  97 /  40  30  30  20
LWT  53  85  52  89 /  50  20  30  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 9 PM MDT Wednesday for Hill County-Northern
Blaine County.

&&

http://www.weather.gov/greatfalls

Special Weather Statement
National Weather Service Great Falls MT
450 PM MDT Tue May 26 2026

MTZ315-316-262330-
Upper Blackfoot and MacDonald Pass MT-Gates of the Mountains MT-
450 PM MDT Tue May 26 2026

...A STRONG THUNDERSTORM WILL IMPACT SOUTHWESTERN LEWIS AND CLARK
COUNTY THROUGH 530 PM MDT...

At 450 PM MDT, Doppler radar was tracking a strong thunderstorm 17
miles southeast of Lincoln, or 24 miles northwest of Helena, moving
northwest at 15 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...
Lincoln.

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.

&&

LAT...LON 4698 11266 4676 11230 4666 11240 4666 11242
      4670 11242 4670 11254 4684 11254 4684 11280
      4699 11280
TIME...MOT...LOC 2250Z 131DEG 20KT 4675 11247

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

RCG

Special Weather Statement
National Weather Service Great Falls MT
508 PM MDT Tue May 26 2026

MTZ320-323-324-326-270000-
Missouri Headwaters MT-Big Belt, Bridger and Castle Mountains MT-
Canyon Ferry Area MT-Gallatin Valley MT-
508 PM MDT Tue May 26 2026

...STRONG THUNDERSTORMS WILL IMPACT SOUTHWESTERN BROADWATER...
NORTHEASTERN MADISON...SOUTHEASTERN JEFFERSON AND NORTHERN GALLATIN
COUNTIES THROUGH 600 PM MDT...

At 507 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from 6 miles southwest of Manhattan to near
Belgrade. Movement was northwest at 30 mph.

HAZARD...Wind gusts of 45 to 55 mph and half inch 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...
Bozeman, Belgrade, Three Forks, Manhattan, Logan, Amsterdam, Trident,
Church Hill, Willow Creek, Menard, Madison Buffalo Jump State Park,
and Missouri Headwaters State Park.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

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

&&

LAT...LON 4603 11188 4604 11096 4580 11079 4572 11079
      4568 11158
TIME...MOT...LOC 2307Z 120DEG 26KT 4578 11142 4574 11116

MAX HAIL SIZE...0.50 IN
MAX WIND GUST...55 MPH

Wilson

Special Weather Statement
National Weather Service Great Falls MT
520 PM MDT Tue May 26 2026

MTZ313-317-270015-
Judith Basin County and Judith Gap MT-
Little Belt and Highwood Mountains MT-
520 PM MDT Tue May 26 2026

...A STRONG THUNDERSTORM WILL IMPACT SOUTHEASTERN JUDITH BASIN AND
SOUTHWESTERN FERGUS COUNTIES THROUGH 615 PM MDT...

At 520 PM MDT, Doppler radar was tracking a strong thunderstorm 17
miles south of Hobson, or 21 miles north of Harlowton, moving
northwest at 25 mph.

HAZARD...Wind gusts up to 50 mph and penny 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...
Utica and Sapphire Village.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4675 10976 4670 10982 4671 10987 4675 10996
      4674 11003 4675 11005 4674 11006 4690 11041
      4706 11017
TIME...MOT...LOC 2320Z 128DEG 21KT 4675 10988

MAX HAIL SIZE...0.75 IN
MAX WIND GUST...50 MPH

Glinskas