Special Weather Statement, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
828 PM MDT Mon Aug 30 2021

.SYNOPSIS...

An increasing southwest breeze will bring haze and wildfire smoke
back into Southwest Montana. An isolated overnight light rain
shower is possible near or east of the Havre area. Otherwise,
mild, dry, and breezy conditions continue through Tuesday.
Temperatures turn cooler on Wednesday following a dry cold front.
This front will also help clear the haze and smoke from the
region.

&&

.UPDATE...

Scattered showers and thunderstorms continue to move northeastward
through southwestern and north central Montana this evening.
Convective activity has been more widespread and intense than
earlier forecasts projected. Main threat from this activity has
been strong and erratic outflow winds with locally heavy rainfall.
Best example of this was a wind gust of 78 mph at the Bozeman
Airport shortly after 5 PM. Also, while heavy rainfall has been
observed from some of this activity, the storms forward motion of
45 mph has limited rainfall amounts to only a few hundreths of an
inch. Forecast was updated earlier this evening to increase PoPs
from less than 10 percent up towards 20 to 40 percent. Have also
added wording for gusty winds and locally heavy rainfall to all
forecast products. Early evening model updates suggest that the
convective showers will continue through the evening and into the
overnight hours with coverage shifting into northeastern portions
of the forecast area. Will continue to monitor this activity and
additional updates will be issued as needed. mpj

&&

.AVIATION...
545 PM MDT Mon Aug 30 2021 (31/00Z TAF period)

Southwesterly flow aloft over Montana will continue to bring
few/scattered mid- and high-level clouds with isolated, mainly
mountain, showers and a few thunderstorms tonight through Tuesday
evening. Although radar echoes showing these showers look fairly
weak, please note that one shower created a 68 knot (78 mph) wind
gust at the KBZN terminal this afternoon. Areas of smoke and haze
will reduce visibility at times but widespread VFR conditions
should prevail. mpj

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

&&

.PREV DISCUSSION...
/ISSUED 545 PM MDT Mon Aug 30 2021/

Satellite imagery shows increasing wildfire smoke returning to
Southwest Montana on the dry southwesterly flow aloft. Scattered
cumulus are developing over mountain ridgetops. These most likely
do not have enough moisture to develop into showers, but some of
the latest CAM guidance carries a slight chance for light showers
into north-central Montana overnight. Although excessively dry,
there is a subtle upper level shortwave that may be able to
support some of this activity.

On Tuesday the southwesterly flow aloft strengthens with a
deepening synoptic scale trough over the Pacific Northwest.
Elevated to near-critical fire weather conditions develop Tuesday
afternoon, especially over ridgetop areas exposed to the
increasing mid-level winds and where humidity will remain low.
Most areas on Tuesday afternoon should see minimum relative
humidity drop well into the teens. A dry cold front works through
the region on Tuesday, turning winds to west or northwest and
increasing for a short time due to pressure rises behind the
front. PN

Wednesday through next Monday...The low pressure trough axis
is forecast to generally remain over Alberta through the Pacific
Northwest to off the California coast at least through the day on
Thursday. This will keep the forecast area under the southwesterly
flow aloft, which will keep a chance for showers and
thunderstorms at times mainly over the area along and east of a
Havre to Dillon line, but it will also keep temperatures below
normal. Forecast models then diverge on solutions for Friday
through the Labor Day holiday weekend, so will stay with the
consensus solution of the National Blend of Models (NBM). This
keeps a chance of showers and thunderstorms mainly over southwest
Montana on Friday, likely due to a more westerly flow aloft
returning to the area as weak high pressure ridging moves into the
area. This ridging should help keep the area dry through Sunday,
as temperatures warm back up to near normal with periods of breezy
westerly winds. However, a weak low pressure trough will then
cool temperatures a bit as it brings a chance for showers for
Labor Day (Monday).
-Coulston

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  49  82  42  74 /  20   0  10   0
CTB  48  72  39  68 /  10   0   0   0
HLN  52  83  46  76 /  10   0   0   0
BZN  47  86  42  76 /   0   0   0   0
WYS  33  76  35  72 /   0   0   0  10
DLN  45  82  39  76 /   0   0   0   0
HVR  53  83  46  74 /  20   0  20   0
LWT  51  83  46  72 /  20  10  20   0

&&

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

http://www.weather.gov/greatfalls

Special Weather Statement
National Weather Service Great Falls MT
926 PM MDT Mon Aug 30 2021

MTZ012-013-046-048-049-310400-
Chouteau MT-Cascade MT-Southern Rocky Mountain Front MT-
Eastern Teton MT-Eastern Pondera MT-
926 PM MDT Mon Aug 30 2021

...Strong thunderstorms will impact portions of southeastern
Pondera, southeastern Teton, southwestern Chouteau and northern
Cascade Counties through 1000 PM MDT...

At 925 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from 6 miles south of Brady to 8 miles west of Great
Falls. Movement was northeast at 15 mph.

HAZARD...Winds in excess of 30 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Great Falls, Dutton, Brady, Black Eagle, Power, Collins, Portage,
Ulm, Malmstrom Afb, Vaughn, First Peoples Buffalo Jump State Park and
Sun River.

This includes the following highways...
 Interstate 15 between mile markers 267 and 330.
 Highway 200 between mile markers 135 and 139.
 Highway 87 between mile markers 4 and 18.
 Highway 89 between mile markers 9 and 17, and between mile markers
86 and 8.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4750 11095 4736 11168 4791 11212 4822 11158
      4822 11146
TIME...MOT...LOC 0325Z 238DEG 12KT 4795 11186 4751 11148

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...30 MPH

SC

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