Special Weather Statement, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
218 PM MDT Tue Jul 20 2021

.SYNOPSIS...

A day to day chance for mostly afternoon and evening showers and
thunderstorms can be expected through Thursday. Gusty westerly
winds may develop over the plains on Thursday and Friday, which
will bring fire weather concerns. Temperatures will generally
remain well above normal for the remainder of the forecast period.

&&

.DISCUSSION...

Remainder of this afternoon through Wednesday...Primary concern
over the period will be scattered, mostly afternoon and evening,
showers and thunderstorms. These storms will produce lightning,
gusty winds, and brief heavy rains. Some localized flooding will
be possible especially this afternoon and evening as PWATs climb
near to above 1", which is 2 to 3 standard deviations above
normal. This will be especially true if a storm moves over a fire
burn scar area. Monsoonal moisture continues to stream
northeastward and over the region this afternoon and has lead to
the development of scattered showers and thunderstorms over the
southwest and will likely expand northeastward into Central MT
later this afternoon, mostly impacting areas roughly along and
southeast of a Helena to Lewistown line. Thunderstorm activity is
still possible northwest of this line , but confidence of storm
development lower for this area. As mentioned earlier, PWATs are
running anomalously high, which increases the potential for heavy
rainfall, especially where the training of showers and
thunderstorms occurs, and/or if storm develop over burn scars.
Shower and thunderstorm activity is expected to decrease in
coverage tonight, though some showers and perhaps a few storms
can't be completely ruled out. Another shortwave moves through the
region on Wednesday and will likely bring another round of
showers and storms moving from southwest to northeast. The same
thunderstorm concerns can be expected for Wednesday despite
slightly less moisture than today. -RCG

Wednesday night through next Tuesday...Primary concern over the
period will be the breakdown of the H500 ridge by the trough
currently moving towards the Pacific Northwest/BC (this morning)
during the Wednesday night through Thursday night timeframe. This
ridge breakdown will result in increasing westerly surface winds,
especially over Central and North Central Montana during the day
on Thursday, as a Pacific front moves across the Northern Rockies.
High temperatures throughout the period will remain on the warm
side, with most locations rising into the 80s and 90s. The
expected combination of winds, very warm temperatures, and low
relative humidity has lead to the issuance of a Fire Weather Watch
for zones 112, 113, 114, and 116 for Thursday afternoon and early
evening. Any new discrete lightning fire starts from today or
Wednesday could quickly grow in these condtions. Precipitation
chances are not expected to be as widespread as compared to the
first half of the work week, but isolated to scattered showers and
thunderstorms are possible on Thursday southeast of a Lincoln, to
Great Falls, to Chinook line. - Moldan/RCG

&&

.AVIATION...
1148 AM MDT Tue Jul 20 2021 (20/18Z TAF period)

Scattered showers and thunderstorms are beginning to initiate over
SW MT early this afternoon and will track NE through the evening
before diminishing. Most of the activity will occur along and south
of a KHLN to KLWT line, but a few storms will be possible further
north as well. Gusty outflow winds could impact areas near these
storms along with brief MVFR conditions and mountain obscuration in
precipitation immediately under cells. Surface winds will generally
remain light outside of any thunderstorm activity. -Hoenisch/RCG

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

&&

.FIRE WEATHER...

While scattered to numerous showers and thunderstorms are
expected today, with most if not all being on the wet side, recent
heat/dryness will likely leave fuels receptive to new lightning
ignitions despite the higher humidity and wetting rain potential.
The ridge which has dominated the pattern as of late is then
expected to be broken down Wednesday night and through the day on
Thursday. Strong and gusty winds, especially during the afternoon
and evening hours on Thursday, are expected across the region due
to this ridge breakdown. This will likely bring elevated fire
weather conditions during the day on Thursday, especially
considering the potential for emerging holdover fires from
lightning earlier in the week. As a result, a Fire Weather Watch
has been issued for Thursday afternoon and evening for fire zones
112, 113, 114, and 116.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  61  92  57  92 /  30  30  30  20
CTB  56  88  53  84 /  20  40  20  10
HLN  61  92  61  93 /  50  60  30  20
BZN  56  92  56  92 /  50  30  30  30
WYS  45  82  46  83 /  50  30  20  40
DLN  54  88  54  89 /  50  30  30  30
HVR  63  95  60  94 /  10  40  40  10
LWT  61  89  59  91 /  20  40  40  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Thursday afternoon through Thursday
evening Eastern Glacier/Toole/Central/Eastern Pondera/Liberty...
Hill and Blaine Counties...Lewis and Clark National Forest Rocky
Mountain District-Rocky Mountain Front...Lincoln Ranger District
of the Helena National Forest.

Fire Weather Watch from Thursday afternoon through Thursday
evening Deerlodge/Western Beaverhead National Forest.

Red Flag Warning until midnight MDT tonight Gallatin National
Forest.

&&

http://www.weather.gov/greatfalls

Special Weather Statement
National Weather Service Great Falls MT
112 PM MDT Tue Jul 20 2021

MTZ008-015-052-202130-
Beaverhead-Madison-Jefferson-
Including the cities of Big Hole Pass, Wisdom, Dillon,
Chief Joseph Pass, Monida Pass, Wise River, Ennis, Norris Hill,
Raynolds Pass, Twin Bridges, Virginia City, Montana City,
Boulder, Boulder Hill, Elk Park Pass, Homestake Pass,
and Whitehall
112 PM MDT Tue Jul 20 2021

...Scattered Thunderstorms Developing This Afternoon...

Scattered thunderstorms are developing and becoming more
widespread this afternoon across portions of Beaverhead, Madison
and Jefferson counties. Thunderstorms are drifting from the
southwest toward the northeast at around 10 mph. Expect locally
heavy rainfall, with up to one-half inch possible. Have a plan to
seek shelter indoors from lightning if a thunderstorm moves toward
your location.

Special Weather Statement
National Weather Service Great Falls MT
238 PM MDT Tue Jul 20 2021

MTZ052-053-202100-
Broadwater-Jefferson-
238 PM MDT Tue Jul 20 2021

...AN AREA OF STRONG THUNDERSTORMS WILL AFFECT CENTRAL BROADWATER...
EAST CENTRAL JEFFERSON COUNTIES...

At 236 PM MDT, strong thunderstorms were clustered 8 miles west of
Toston, or 11 miles southwest of Townsend, moving east northeast at
10 mph.

Winds in excess of 30 mph are possible with this storm.

Locations impacted include...
Townsend, Toston, Silos and Radersburg.

This includes Highway 12 between mile markers 1  and 14, and between
mile markers 71 and 100.

Torrential rainfall is also occurring with these storms, and may
cause localized flooding. Do not drive your vehicle through flooded
roadways.

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.

If you are on or near Canyon Ferry Lake, get out of the water and
move indoors or inside a vehicle. Remember, lightning can strike out
to 10 miles from the parent thunderstorm. If you can hear thunder,
you are close enough to be struck by lightning. Move to safe shelter
now! Do not be caught on the water in a thunderstorm.

LAT...LON 4625 11192 4652 11138 4620 11112 4619 11117
      4619 11134 4613 11134 4610 11138 4611 11140
      4609 11140 4598 11172
TIME...MOT...LOC 2036Z 247DEG 24KT 4617 11162

RCG