Special Weather Statement, 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
545 PM MDT Thu Aug 6 2020

MTZ012-053-054-070015-
Broadwater-Cascade-Meagher-
545 PM MDT Thu Aug 6 2020

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT NORTHERN BROADWATER...
NORTHWESTERN MEAGHER...NORTHWESTERN JUDITH BASIN AND SOUTHEASTERN
CASCADE COUNTIES...

At 544 PM MDT, radar indicated strong thunderstorms were located
along a line extending from 20 miles southwest of Belt to 30 miles
southeast of Cascade to 27 miles northwest of White Sulphur Springs.
Movement was northeast at 40 mph.

Winds up to 40 mph are possible with these storms.

Locations impacted include...
Neihart, Sluice Boxes State Park and Monarch.

This includes the following highways...
 Highway 200 between mile markers 1 and 7.
 Highway 89 between mile markers 33 and 70.

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 4675 11150 4719 11131 4739 11076 4732 11077
      4730 11079 4725 11079 4723 11077 4710 11077
      4709 11069 4699 11063 4689 11064
TIME...MOT...LOC 2344Z 221DEG 35KT 4718 11124 4697 11122 4681 11135

RCG

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

MTZ014-052-053-070015-
Broadwater-Jefferson-Central and Southern Lewis and Clark-
549 PM MDT Thu Aug 6 2020

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT SOUTHERN LEWIS AND
CLARK...NORTHWESTERN BROADWATER...AND NORTHEASTERN JEFFERSON
COUNTIES...

At 548 PM MDT, radar indicated strong thunderstorms were located
along a line extending from 6 miles southwest of Lincoln to 11 miles
south of Wolf Creek to 11 miles northeast of Boulder to 12 miles
north of Whitehall. Movement was northeast at 40 mph.

Winds up to 50 mph are possible with these storms.

Locations impacted include...
Helena, Townsend, Boulder, Lincoln, East Helena, Montana City, Wolf
Creek, Wickes, York, Alhambra, Corbin, Spring Meadow Lake State Park,
Austin, Elkhorn State Park, Marysville, Winston, Radersburg, Craig,
Silos and Clancy.

This includes the following highways...
 Interstate 15 between mile markers 163 and 237.
 Highway 200 between mile markers 68 and 97.

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 4718 11242 4710 11179 4692 11179 4689 11161
      4684 11164 4680 11159 4681 11152 4663 11141
      4620 11153 4595 11207 4616 11218 4632 11216
      4646 11209 4671 11233 4677 11253 4684 11254
      4684 11280 4691 11280
TIME...MOT...LOC 2348Z 229DEG 36KT 4687 11274 4683 11207 4635 11195
4605 11202

RCG

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