Special Weather Statement, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
535 PM MDT Sat Aug 1 2020

...UPDATED AVIATION SECTION AND EVENING PUBLIC FORECAST PERIOD...

.SYNOPSIS...

Other than a few thunderstorms over the mountains this afternoon
and evening, mostly dry weather is expected through the remainder
of the weekend. It will remain warm, with temperatures in the
upper 80s to mid 90s. A change in the pattern will begin on
Tuesday as a system brings widespread rain on Tuesday, followed by
a return to near average temperatures.

&&

.DISCUSSION...

535 pm Update...Have added mention of scattered thunderstorms over
the Little Belt Mountains of Central Montana and increased the
coverage to mostly scattered storms over Southwest Montana south of
Interstate 90 to better reflect current conditions.  Coulston

Clear, but hazy, skies are currently observed across most of the
CWA this afternoon. However, current radar and satellite imagery
do show that diurnal showers and thunderstorms are beginning to
pop up over the southwestern mountains. These will continue
develop through the remainder of the afternoon and evening, with
additional development expected along the Continental Divide
within the next few hours. For the most part, these showers and
storms should not be overly strong, though some gusty outflow
winds and/or small hail cannot be entirely ruled out. Temperatures
continue to be around 0-4 degrees higher than they were at this
time yesterday, so afternoon highs should be slightly warmer than
yesterday's.

Any convective activity should once again dissipate rather
quickly, and tonight will likely be rather cloudy across the CWA
as debris clouds from the convection slide eastward. This should
keep overnight lows on the mild side, with most locales in the mid
50s- mid 60s, though a few of the western valleys may still
manage to dip into the 40s.

Upper level ridging remains in place through the beginning of the
work week, which should keep Sunday and Monday hot and mostly dry,
save for isolated afternoon thunderstorms. However, the previously
advertised ridge breakdown is still expected on Tuesday as an
upper level low moves to our north. Ensemble guidance is
converging on a less-windy solution than one would normally expect
for a ridge breakdown, so wind speeds have been lowered a bit from
previous forecasts. Showers and thunderstorms should also be
rather widespread, and it is looking like there is a decent chance
of a wetting rain associated with these showers.

Looking further into next week, models seem fairly confident that
temperatures will remain steady or slowly climb as southwesterly
flow sets up aloft. Rain chances will likely be hard to come by
after Tuesday, aside from a few afternoon showers and
thunderstorms.

Ludwig

&&

.AVIATION...
Updated 535 PM MDT Sat Aug 1 2020 (02/00Z TAF Period)

VFR conditions will mostly persist over North Central and Southwest
Montana through at least the next 24 hours, but brief periods of
MVFR conditions are possible with thunderstorms. As of 23Z, isolated
to scattered thunderstorms have developed over the mountains of the
Rocky Mountain Front, the Little Belt Mountains, and over the
mountains of Southwest Montana south of Interstate 90. The unstable
airmass will likely cause a few more storms to fill in over the
Continental Divide west of KHLN and KGTF through 02Z, which should
move east over the KEKS, KWYS, KBZN, KHLN, KGTF, and KCTB terminals
through around 06Z, but they should diminish after then. Otherwise,
mid level cloudiness will linger overnight, then decrease during the
day on Sunday.  Coulston

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...

Hot temperatures with isolated to scattered showers and
thunderstorms continue through at least Monday. A steady easterly
breeze each day could also produce elevated fire weather concerns
to areas with warm temperatures and low RH values. A cold front
passage Monday evening into Tuesday will help produce more
organized thunderstorm activity with a trend toward cooler
temperatures. Although this is a ridge-breakdown scenario,
forecast guidance has consistently been indicating winds will
remain below criteria that would lead to more critical fire
weather concerns. This suggests that fire weather highlights
won't be necessary, but this situation will continue to be
monitored.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  62  92  62  89 /  10   0  10  40
CTB  59  90  57  88 /  40  10  10  30
HLN  60  94  61  91 /  30   0  10  50
BZN  57  93  56  92 /  40   0  10  50
WYS  48  88  43  86 /  30   0  10  30
DLN  55  90  55  88 /  30   0  10  40
HVR  61  92  60  94 /   0   0  10  20
LWT  57  87  56  89 /   0   0  10  30

&&

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

http://www.weather.gov/greatfalls

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Special Weather Statement
National Weather Service Great Falls MT
450 PM MDT Sat Aug 1 2020

MTZ012-012315-
Cascade-
450 PM MDT Sat Aug 1 2020

...AN AREA OF STRONG THUNDERSTORMS WILL AFFECT SOUTHEASTERN CASCADE
COUNTY...

At 448 PM MDT, strong thunderstorms were clustered over the Little
Belt Mountains, about 24 miles southwest of Geyser, or 31 miles west
of Stanford, moving northwest at 10 mph.

Heavy rain, winds in excess of 30 mph, and pea size hail are
possible with this storm.

Locations impacted include...
Neihart and Monarch.

This includes Highway 89 between mile markers 35 and 57.

If outdoors, consider seeking shelter inside a building.

Heavy rainfall with this storm may cause rapid runoff on steep
slopes with localized flooding. Do not drive your vehicle through
flooded roadways.

Frequent 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 4689 11075 4690 11082 4698 11092 4700 11099
      4705 11109 4708 11108 4709 11112 4721 11079
      4718 11076 4710 11077 4709 11069 4704 11064
      4693 11064
TIME...MOT...LOC 2248Z 151DEG 7KT 4702 11086

SC

Special Weather Statement
National Weather Service Great Falls MT
454 PM MDT Sat Aug 1 2020

MTZ008-015-012330-
Madison-Beaverhead-
454 PM MDT Sat Aug 1 2020

...AN AREA OF STRONG THUNDERSTORMS WILL AFFECT SOUTHEASTERN MADISON
AND SOUTHEASTERN BEAVERHEAD COUNTIES...

At 453 PM MDT, strong thunderstorms were clustered 15 miles north of
Kilgore Idaho, or 18 miles north of Idmon Idaho, moving east at 10
mph.

Heavy rain, winds in excess of 30 mph, and pea size hail are
possible with this storm.

Locations impacted include...
Lakeview.

If outdoors, consider seeking shelter inside a building.

Heavy rainfall with this storm may cause rapid runoff on steep
slopes with localized flooding. Do not drive your vehicle through
flooded roadways.

Frequent 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 4456 11187 4454 11199 4472 11197 4475 11163
      4456 11164 4456 11171 4454 11172 4454 11175
      4452 11176 4452 11181 4451 11182
TIME...MOT...LOC 2253Z 273DEG 9KT 4463 11188

SC

Special Weather Statement
National Weather Service Great Falls MT
457 PM MDT Sat Aug 1 2020

MTZ055-012330-
Gallatin-
457 PM MDT Sat Aug 1 2020

...A STRONG THUNDERSTORM WILL AFFECT SOUTH CENTRAL GALLATIN COUNTY...

At 456 PM MDT, a strong thunderstorm was located near Henrys Lake
Idaho, moving northeast at 10 mph.

Heavy rain, winds in excess of 30 mph, and pea size hail are
possible with this storm.

Locations impacted include...
West Yellowstone and Yellowstone Village.

This includes the following highways...
 Highway 191 between mile markers 1 and 2.
 Highway 287 near mile marker 18.

If outdoors, consider seeking shelter inside a building.

Heavy rainfall with this storm may cause rapid runoff on steep
slopes with localized flooding. Do not drive your vehicle through
flooded roadways.

Frequent 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 4457 11118 4458 11123 4462 11124 4462 11122
      4465 11127 4468 11127 4473 11132 4481 11119
      4469 11109 4456 11110 4454 11116
TIME...MOT...LOC 2256Z 240DEG 9KT 4462 11131

SC

Special Weather Statement
National Weather Service Great Falls MT
618 PM MDT Sat Aug 1 2020

MTZ009-048-020045-
Southern Rocky Mountain Front-Northern Rocky Mountain Front-
618 PM MDT Sat Aug 1 2020

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT NORTHWESTERN LEWIS AND
CLARK...WEST CENTRAL PONDERA...SOUTH CENTRAL GLACIER AND WESTERN
TETON COUNTIES...

At 616 PM MDT, radar indicated strong thunderstorms were located
along a line extending from 10 miles south of East Glacier Park
Village to 19 miles west of Augusta. Movement was north at 5 mph.

Heavy rain, winds in excess of 30 mph, and half inch hail are
possible with these storms.

Locations impacted include...
East Glacier Park and East Glacier Park Village.

This includes Highway 2 between mile markers 202 and 213.

If outdoors, consider seeking shelter inside a building.

Heavy rainfall with these storms may cause rapid runoff on steep
slopes with localized flooding. Do not drive your vehicle through
flooded roadways.

To report severe weather, contact your nearest law enforcement
agency. They can relay your report to the National Weather Service
office in Great Falls.

LAT...LON 4850 11319 4816 11273 4750 11259 4733 11279
      4789 11310 4795 11299 4795 11292 4798 11288
      4801 11289 4804 11295 4813 11301 4812 11305
      4815 11306 4817 11323 4824 11323 4830 11334
TIME...MOT...LOC 0016Z 191DEG 6KT 4829 11329 4747 11281

SC