Severe Thunderstorm Warning 62, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
342 PM MDT Sun Jun 15 2025

.KEY MESSAGES...

 - Scattered showers and thunderstorms, mainly in the afternoon
   and evening, through Tuesday.

 - A few thunderstorms look to be on the strong side through the afternoon
   and evening today, capable of large hail and strong wind
   gusts.

 - After a brief break from precipitation chances Wednesday,
   additional rounds of precipitation return Thursday into the
   weekend, with this weekend on the cooler side.

&&

.DISCUSSION...

 - Meteorological Overview:

The remainder of this afternoon and evening:

Shortwave troughing within a southwesterly flow aloft is interacting
with ample surface moisture this afternoon to produce scattered
showers and thunderstorms. Per the TFX 18Z sounding, ample
instability is already in place (Sfc based cape in excess of 1,500
j/kg), with effective shear in excess of 40kts. The relatively
straight nature of the hodograph suggests hail is the greatest
threat from organized thunderstorms (supercells), at least
initially, with observed significant hail parameter in excess of 1
suggesting significant hail 2+" in diameter is not out of the
question.

The area most favored for the development of these stronger
thunderstorms looks to be across eastern portions of Central Montana
(Judith Basin and Fergus counties) and vicinity. Strong wind gusts
will also be a concern, though hail is the main threat. Given the
slower nature of thunderstorms today, and the tendency for some
storms to at least briefly anchor to terrain, heavy rainfall will
also be a concern with modest PWATs in place.

This activity moves eastward this evening, largely exiting by 9 PM
or so. There does look to be some lingering support and instability
for elevated showers and perhaps a thunderstorm or two tonight,
mostly between I-90 and US-12.

Monday and Tuesday:

Another wave within southwesterly flow aloft moves across the region
Monday afternoon and evening. Although there looks to be at least
low-end instability over the vast majority of the region, the area
with the greatest shear and instability combination looks to be
across Southwest Montana, east of I-15. This area is highlighted by
a marginal risk from the Storm Prediction Center for severe
thunderstorms. Both gusty winds and hail will be the concern with
the thunderstorms that form.

Instability remains heading into Tuesday, though shear diminishes
as weak shortwave ridging develops within a more zonal flow aloft.
Showers and thunderstorms still develop, though look to be less
organized in nature given the weaker shear.

Wednesday and beyond:

A brief period of low-amplitude ridging develops Wednesday, yielding
a brief period of dry weather. Daytime mixing Wednesday should yield
marginally breezy conditions over the plains.

Large scale troughing moves in over the Pacific Northwest Thursday
and into the weekend. Initially this brings about another
opportunity for showers and thunderstorms Thursday and Friday
afternoon and evening. As the system progresses inland and the
core moves over the Northern Rockies, temperatures trend cooler,
with opportunities for precipitation increasing. Uncertainty is
large at this point, but temperatures look at least briefly cool
enough to support light high mountain snow. -AM

 - Forecast Confidence & Scenarios:

Cooler and unsettled weather next weeekend...

Ensembles strongly favor a deep trough moving into the Pacific
Northwest and bringing a return to southwesterly flow aloft to
Northern Rockies by Friday for increased shower and thunderstorm
activity. This will be followed by the trough progressing eastward
in some fashion and bringing cooler and unsettled weather next
weekend. There are some disagreements with the evolution of the
system as it moves through, but there's a general expectation for
near to below average temperatures, breezy conditions, and daily
rounds of precipitation. - RCG

&&

.AVIATION...
15/18Z TAF Period

VFR conditions will prevail across all terminals during this TAF
period outside of during any thunderstorms. The primary aviation
concern for this TAF Period is strong to severe thunderstorms at
all terminals except for the KCTB and KWYS terminals between
15/20Z and 16/04Z. The greatest risk for a severe thunderstorm
capable of producing large (1 inch in diameter) to very large hail
(2+ inches in diameter) and wind gusts in excess of 58 mph is at
the KLWT terminal between 15/22Z and 16/04Z. All thunderstorms
will produce heavy downpours, frequent lightning, small hail, and
gusty, erratic winds. There will be brief periods of mountain
obscuration during any thunderstorm. -IG

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  51  76  51  80 /  20  30  30  20
CTB  44  76  47  78 /   0  20  20  20
HLN  55  75  52  81 /  20  60  40  20
BZN  49  79  47  76 /  40  60  50  40
WYS  38  74  37  69 /  10  30  30  40
DLN  46  78  45  73 /  20  50  40  20
HVR  50  81  51  83 /  40  20  20  30
LWT  49  71  47  72 /  80  50  50  50

&&

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

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