Severe Thunderstorm Warning 48, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
550 PM MDT Tue Aug 22 2023

UPDATED AVIATION SECTION

.SYNOPSIS...

Showers and thunderstorms will be possible each afternoon and
evening through Wednesday as moist, southwest flow aloft persist
over the Northern Rockies. The best coverage of these showers and
storms is expected this afternoon and evening, with more isolated
to scattered precipitation on Wednesday.

&&

.DISCUSSION...

Rest of today through Wednesday...Strong upper level ridge over the
center of the CONUS, with its high centered over the Middle to Lower
Mississippi Valley through Wednesday, will help to maintain moist,
southwest flow over the Northern Rockies as a shortwave trough and
attendant low moves northeast from the Pacific Northwest to over
Central/Southern Alberta (Wednesday night). This moist, southwest
flow aloft combined with fast moving shortwaves embedded within the
overall flow will help to support chances for showers and
thunderstorms this afternoon/tonight and then again Wednesday
afternoon/evening across Southwest through North Central Montana.
The strongest of these embedded shortwaves is expected to lift
northeast over the Northern Rockies from the late evening through
early morning hours on Wednesday, supporting the best coverage of
showers and thunderstorms across the CWA. The coverage of showers
and thunderstorms then Wednesday afternoon/evening is expected to be
more isolated to scattered in nature given the weaker forcing
with the final shortwave. Despite the weaker shortwave arriving
Wednesday afternoon/evening, increasing cross barrier flow ahead
of this shortwave will lead to stronger surface winds
materializing across the CWA. Latest NBM probabilistic data
suggests a 70% chance or greater of wind gusts reaching/exceeding
34kts across the East Glacier Park Region, Northern High Plains
adjacent to the RMF, and Eastern Glacier/ Western Toole/Central
Pondera Counties during the day on Wednesday, with a 80% chance or
greater of reaching/exceeding 22kts across all of Southwest
through North Central Montana. Despite these gusty winds during
the day on Wednesday, recent precipitation and sub-critical
relative humidity values will help to mitigate any fire weather
concerns. - Moldan

Thursday through Tuesday...The upper level ridge over the Plains
will slowly retrograde westward and then rebuild over the
Northern Rockies by early next week. Generally warm temperatures
are expected Thursday and Friday, with temperatures then becoming
hot over the weekend and into early next week. Afternoon highs are
forecast to be in the mid 90s by early next week. There will be
isolated storms during this period, but confidence in any storm
activity is generally low, as the upper level ridge builds in and
tries to dry things out once again. Brusda

&&

.AVIATION...
550 PM MDT Tue Aug 22 2023 (23/00Z TAF Period)

VFR conditions are mostly expected across North Central, Central,
and Southwest Montana through at least 24/00Z. However, brief
periods of MVFR/IFR conditions are possible with thunderstorms
through around 06Z.

An unstable southwesterly flow aloft tapping into Pacific moisture
will continue scattered showers and thunderstorms across much of the
area through around 06Z. Some storms could cause gusts in excess of
50 kt with some heavy rainfall and hail. Otherwise, VFR ceilings
will mostly continue after 06Z, with a possibility of a few rain
showers through around 12Z. Westerly winds will increase and become
gusty after 16Z, with the main threat for additional showers and
thunderstorms remaining over Central Montana. -Coulston

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  56  83  48  81 /  60  20  10   0
CTB  53  78  44  75 /  40  10   0   0
HLN  59  83  52  83 /  30  30   0   0
BZN  53  82  48  82 /  20  10  10   0
WYS  45  72  38  75 /  40  20  10   0
DLN  50  78  45  79 /  30  10  10   0
HVR  58  85  50  83 /  60  20  20   0
LWT  55  81  49  78 /  20  20  20   0

&&

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

http://www.weather.gov/greatfalls

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Special Weather Statement
National Weather Service Great Falls MT
627 PM MDT Tue Aug 22 2023

MTZ312-230100-
Cascade County below 5000ft MT-
627 PM MDT Tue Aug 22 2023

...A strong thunderstorm will impact portions of north central
Cascade County through 700 PM MDT...

At 626 PM MDT, Doppler radar was tracking a strong thunderstorm near
Great Falls, moving north at 30 mph.

HAZARD...Winds in excess of 40 mph and pea size hail.

SOURCE...Radar indicated.

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

Locations impacted include...
Great Falls, Black Eagle, Ulm, Malmstrom Afb, Sand Coulee, Tracy,
Vaughn and First Peoples Buffalo Jump State Park.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4735 11122 4734 11161 4760 11164 4764 11119
      4757 11104 4739 11116
TIME...MOT...LOC 0026Z 192DEG 25KT 4743 11126

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

JAF