Severe Thunderstorm Warning 53, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
306 PM MDT Thu Aug 6 2020

.SYNOPSIS...

Scattered showers and thunderstorms in an unstable southwest flow
aloft will spread northeast across the region through this evening.
Gusty winds and brief rainfall will accompany most storms, but a
few stronger storms could produce damaging winds and small hail.
A Pacific cold front will then move through the area overnight,
bringing cooler, but still dry air to the area on Friday, along
with gusty westerly winds. Dry and breezy conditions with slightly cooler
than normal temperatures will persist through the weekend with
temperatures warming again next week.

&&

.DISCUSSION...

Tonight through Saturday...

Thunderstorm development currently underway across SW and central
MT will lift northeast across central and eastern portions of
north-central MT through this evening. Warm/dry conditions in the
lower levels will set up a favorable environment for strong
outflow winds with these storms along with some potential for hail
in the strongest cells. Additional thunderstorm development
likely later this afternoon and evening over western MT ahead of
the main upper level trough moving inland across WA, and this
activity could bring another round showers and thunderstorms later
this evening. Surface cold front ahead of the trough will move
east across the continental divide this evening and sweep east
most of the forecast area overnight. Westerly winds and drier air
behind the front will bring clearing and an end to precipitation
from west to east late tonight with windy conditions developing
initially along the Rocky Mtn front tonight then spreading east
across most of the forecast area by Friday morning. Strongest
winds aloft move across the region Friday morning but westerly
flow aloft remains quite strong (for early August) through Friday
evening. Areas along the northern Rocky Mtn front and the east
side of Glacier National Park could see a period of wind gusts
over 50 mph early Fri morning as the strongest winds aloft pass in
conjunction with a strong pressure gradient across the Rockies.
Gusts in to 25 to 35 mph range are likely further east across much
of north-central MT beginning Friday morning and continuing
through Friday evening before diminishing. Winds will not be as
strong across SW MT, but afternoon gusts of 20-30 mph are likely.
Temperatures will be 10-20 degrees cooler for most areas on Friday
with afternoon temperatures ranging from the lower 70s near the
Canadian border to the mid 80s across the SW MT valleys. Winds
decrease Friday night but breezy conditions will likely redevelop
on Saturday. Hoenisch

Sunday through next Thursday...

Weak upper level ridging will return to Montana early next week,
which should keep the area dry as temperatures slowly warm back up
to normal by Tuesday. Another low pressure trough will then bring
a good chance for showers and thunderstorms to the area once
again Wednesday and Thursday (and possibly longer), along with
cooler than normal temperatures. Coulston

&&

.AVIATION...
Updated 1134 AM MDT Wed Aug 6 2020 (06/18Z TAF Period)

Showers and areas of broken mid level clouds will continue to lift
north across the region through early this afternoon with
thunderstorm development beginning across SW MT. Thunderstorm
coverage will increase this afternoon and continue through this
evening with greatest concentration shifting from central MT this
afternoon to eastern portions of North-central MT this evening.
Thunderstorms this afternoon and evening could produce strong
outflow winds with gusts in excess of 40kts while potential for
heavy rain and possible hail will be more isolated and limited to
areas directly beneath the thunderstorm cells. Showers and a few
isolated thunderstorms along with broken mid level cloud-cover could
linger beyond this evening with a cold front shifting winds to west
late tonight followed by clearing. Hoenisch

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

NOTE: Amendments not scheduled for Ennis (KEKS) due to ongoing
runway closure.

&&

.FIRE WEATHER...

Thunderstorm this afternoon and evening will increase the potential
for lightning strikes on drying fuels. Wetting precipitation is
possible from some storms, but the chance for new fire starts will
increase. The cold front responsible for the storms today will
move east of the area overnight, bringing cooler temperatures for
Friday, but afternoon relative humidity will fall into the 15 to
25 percent range for much of the area with westerly winds gusting
to 30 mph at times, especially across north-central MT. Breezy
winds with relatively dry conditions will continue into the day on
Saturday, though winds speeds will not be as strong and mainly
limited to the afternoon period.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  55  78  48  81 /  40   0   0   0
CTB  52  74  48  76 /  20   0   0   0
HLN  53  80  48  84 /  40   0   0   0
BZN  51  84  46  86 /  30   0   0   0
WYS  44  80  40  79 /  20  10   0   0
DLN  49  80  44  81 /  30   0   0   0
HVR  58  79  51  84 /  40   0   0   0
LWT  54  79  48  82 /  50   0   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon to 9 PM MDT Friday Central and
Eastern Lewis and Clark National Forest Areas...Chouteau and
Fergus Counties...Eastern Glacier/Toole/Central/Eastern
Pondera/Liberty...Helena and Townsend Ranger Districts of the
Helena National Forest...Hill and Blaine Counties...Lewis and
Clark National Forest Rocky Mountain District-Rocky Mountain
Front...Lincoln Ranger District of the Helena National Forest.

&&

http://www.weather.gov/greatfalls

Special Weather Statement
National Weather Service Great Falls MT
156 PM MDT Thu Aug 6 2020

MTZ051-062030-
Fergus-
156 PM MDT Thu Aug 6 2020

...A STRONG THUNDERSTORM WILL AFFECT NORTHWESTERN FERGUS COUNTY...

At 156 PM MDT, a strong thunderstorm was located 11 miles east of
Denton, or 19 miles northwest of Lewistown, moving northeast at 15
mph.

Winds in excess of 40 mph and pea size hail are possible with this
storm.

Locations impacted include...
Danvers.

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.

LAT...LON 4716 10967 4726 10985 4758 10974 4735 10930
TIME...MOT...LOC 1956Z 217DEG 15KT 4726 10972

RCG

Special Weather Statement
National Weather Service Great Falls MT
214 PM MDT Thu Aug 6 2020

MTZ015-062045-
Madison-
214 PM MDT Thu Aug 6 2020

...A STRONG THUNDERSTORM WILL AFFECT EAST CENTRAL MADISON COUNTY...

At 213 PM MDT, a strong thunderstorm was located over Ennis, or 11
miles east of Virginia City, moving northeast at 15 mph.

Winds in excess of 40 mph are possible with this storm.

Locations impacted include...
Ennis, Jeffers and Mcallister.

This includes Highway 287 between mile markers 45 and 61.

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.

LAT...LON 4528 11173 4537 11184 4559 11162 4538 11136
TIME...MOT...LOC 2013Z 230DEG 14KT 4536 11172

RCG

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Special Weather Statement
National Weather Service Great Falls MT
259 PM MDT Thu Aug 6 2020

MTZ008-015-062130-
Madison-Beaverhead-
259 PM MDT Thu Aug 6 2020

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT MADISON...SOUTHEASTERN
BEAVERHEAD...

At 257 PM MDT, radar indicated strong thunderstorms were located
along a line extending from near Harrison to 19 miles southeast of
Dillon to 18 miles southwest of Lima. Movement was east at 10 mph.

Winds up to 40 mph are possible with these storms.

Locations impacted include...
Virginia City, Ennis, Lima, Alder, Pony, Monida, Harrison, Norris,
Dell, Bannack Pass, Mcallister, Lakeview, Laurin, Cameron, Snowline,
Jeffers, Raynolds Pass and Red Rock Pass.

This includes the following highways...
 Interstate 15 between mile markers 1  and 28 .
 Highway 287 between mile markers 1  and 6.

Cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

LAT...LON 4449 11303 4579 11179 4564 11153 4564 11136
      4475 11138 4470 11149 4466 11147 4459 11153
      4456 11149 4456 11171 4451 11182 4456 11187
      4452 11211 4457 11229 4453 11236 4445 11239
      4450 11274 4444 11283 4438 11282 4436 11285
TIME...MOT...LOC 2057Z 262DEG 8KT 4567 11168 4505 11232 4450 11291

RCG

Special Weather Statement
National Weather Service Great Falls MT
306 PM MDT Thu Aug 6 2020

MTZ051-062130-
Fergus-
306 PM MDT Thu Aug 6 2020

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT NORTHEASTERN FERGUS
COUNTY...

At 304 PM MDT, radar indicated strong thunderstorms were located
along a line extending from near Winifred to 6 miles northwest of Roy
to near Grass Range. Movement was northeast at 25 mph.

Winds up to 40 mph and pea size hail are possible with these storms.

Locations impacted include...
Winifred, Roy, Fergus and Valentine.

This includes Highway 191 between mile markers 28 and 42, and between
mile markers 47 and 87.

Cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

Persons in campgrounds should consider seeking sturdy shelter until
these storms pass.

LAT...LON 4731 10859 4727 10860 4727 10871 4710 10874
      4708 10860 4705 10888 4736 10916 4764 10954
      4780 10927 4778 10913 4781 10898 4775 10892
      4773 10894 4772 10883 4765 10877 4759 10858
      4731 10838
TIME...MOT...LOC 2104Z 239DEG 24KT 4762 10940 4742 10903 4707 10878

RCG

Special Weather Statement
National Weather Service Great Falls MT
314 PM MDT Thu Aug 6 2020

MTZ013-047-051-062145-
Chouteau-Fergus-Blaine-
314 PM MDT Thu Aug 6 2020

...A STRONG THUNDERSTORM WILL AFFECT NORTHWESTERN FERGUS COUNTY...

At 312 PM MDT, a strong thunderstorm was located 15 miles west of
Winifred, or 35 miles north of Lewistown, moving northeast at 25 mph.

Winds in excess of 30 mph and pea size hail are possible with this
storm.

Locations impacted include...
Judith Landing.

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 4744 10972 4757 10987 4787 10961 4756 10944
TIME...MOT...LOC 2112Z 226DEG 20KT 4754 10972

RCG