Severe Thunderstorm Warning 133, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
655 PM MDT Wed Aug 21 2019

.UPDATE...
Mainly focused on making updates to reflect the thunderstorms
pushing through central MT this evening, increasing chances as
these systems advance eastward tonight. Otherwise, the forecast
remains on track with cooling temperatures tomorrow and another
round of showers and isolated thunderstorms. -TP

&&

.SYNOPSIS...
A cold front will cross the state tonight through early Friday,
bringing cooler and breezy weather, along with a chance for
showers and a few thunderstorms to many locations. Breezy and
mostly dry conditions are then expected as the weekend approaches,
with cooler than normal temperatures. -CC

&&

.AVIATION...
Updated 530 PM MDT Wed Aug 21 2019 (22/00Z TAFs)

Mostly VFR conditions are expected for a majority of the TAF period,
with the exception of under any developing thunderstorms this
evening near KHLN. Breezy southeasterly winds have started to pick
up near most terminals as the Pacific trough tracks through the
area. A cold front associated with a Pacific trough is expected to
pass through the region from west to east roughly between 07z and
15z on Thursday. Expect surface winds to shift to a more westerly to
northwesterly direction in the wake of the front. There will also be
an increase in shower activity near and behind this front, which may
introduce a period of MVFR conditions at any terminal. -TP

&&

.FIRE WEATHER...
The last of the seasonably warm days for some time today gives way
to a cooler and breezier weather pattern over the coming days.
A weak disturbance may bring isolated dry t-storms to SW MT this PM.
Warmer and drier conditions return Wed, along with gusty S-SE'ly
breezes. A cold front Wed night into Thu brings some showers and a
few thunderstorms, and a shift to gusty W-NW'ly winds. A wetting
rain appears unlikely for most areas at this time. -CC

&&

.PREV DISCUSSION...
/ISSUED 530 PM MDT Wed Aug 21 2019/
Rest of this Afternoon thru Thursday...High pressure exits to the
east tonight bringing one more mild overnight period with increasing
clouds ahead of an approaching low pressure system with cold front.
Some increase in instability and moisture ahead of the
aforementioned trough will lead to an increasing chance for a few
showers and thunderstorms later this afternoon, primarily along and
northwest of a Helena-to-Lewistown line. Coverage will initially be
isolated but this will change by late tonight into Thursday morning
as the attendant cold front approaches and eventually passes through
the region. As mentioned above, shower and thunder activity will
mostly be confined to the plains through Wednesday night, but will
likely expand to include area in the southwest and central by
Thursday morning and should persist in to the evening hours.
Rainfall totals are not expected to be very heavy, with most
locations receiving a tenth of an inch or less. Note that there
could be localized areas that receive more. Most of this activity
should diminish by the afternoon hours but conditions will likely
not completely dry out until Thursday evening. Breezy west to
northwesterly winds will be present for much of the CWA following
the frontal passage and high temperatures are expected to take about
a 10 degree tumble from today, with 70s and low 80s expected on
Thursday afternoon.

Friday through next Tuesday...Transient ridging briefly builds
builds in for Friday, before an unsettled westerly flow moves in for
the remainder of the forecast period. Disturbances are expected to
pass through this flow, which will keep temperatures below normal
and will provide daily bouts of breezy to windy westerly winds.
Currently, it appears conditions will remain mostly dry until Monday
and Tuesday when a passing trough shift the general flow to a
slightly more unstable northwesterly direction. -CC

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  59  78  52  78 /  60  40  20   0
CTB  57  74  47  77 /  20  60  30   0
HLN  57  78  50  81 /  30  60  30   0
BZN  52  80  47  82 /   0  50  30   0
WEY  43  76  39  77 /   0  40  30   0
DLN  54  76  45  79 /   0  60  20   0
HVR  59  84  50  79 /   0  30  20   0
LWT  56  78  49  74 /  30  50  30  10

&&

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

http://www.weather.gov/greatfalls

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Special Weather Statement
National Weather Service Great Falls MT
653 PM MDT Wed Aug 21 2019

MTZ012-014-048-049-220100-
Cascade-Southern Rocky Mountain Front-Eastern Teton-Central and
Southern Lewis and Clark-
653 PM MDT Wed Aug 21 2019

...OUTFLOW WINDS AFFECT NORTHEASTERN LEWIS AND CLARK... SOUTHEASTERN
TETON AND NORTHWESTERN CASCADE COUNTIES...

At 650 PM MDT, radar indicated outflow winds from distant
thunderstorm along a line extending from 7 miles west of Power to 6
miles north of Fort Shaw to near Fort Shaw to 10 miles northwest of
Cascade. Movement was east at 25 mph.

Winds in excess of 40 mph are possible with this outflow boundary.

Locations impacted include...
Cascade, Fort  Shaw, Fort Shaw, Power, Ulm, Vaughn, First Peoples
Buffalo Jump State Park and Sun River.

This includes the following highways...
 Interstate 15 between mile markers 253 and 273, and between mile
markers 287 and 309.
 Highway 200 between mile markers 132 and 139.
 Highway 89 between mile markers 9 and 17, and between mile markers 1
and 8.

LAT...LON 4781 11159 4757 11145 4747 11142 4741 11147
      4723 11170 4732 11206 4744 11190 4750 11184
      4760 11188 4778 11198
TIME...MOT...LOC 0050Z 277DEG 22KT 4771 11184 4760 11178 4750 11174
4744 11180 4737 11189

Moldan

Special Weather Statement
National Weather Service Great Falls MT
657 PM MDT Wed Aug 21 2019

MTZ012-220130-
Cascade MT-
657 PM MDT Wed Aug 21 2019

...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL CASCADE COUNTY UNTIL 730
PM MDT...

At 657 PM MDT, Doppler radar was tracking a strong thunderstorm near
Cascade, moving northeast at 5 mph.

Nickel size hail and wind gusts up to 50 mph will be possible with
this storm.

This storm will remain over mainly rural areas of central Cascade
County.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with this storm, and may lead
to 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.

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 4721 11161 4725 11167 4743 11158 4723 11132
TIME...MOT...LOC 0057Z 238DEG 6KT 4728 11159

Moldan

Special Weather Statement
National Weather Service Great Falls MT
701 PM MDT Wed Aug 21 2019

MTZ012-049-220130-
Cascade MT-Eastern Teton MT-
701 PM MDT Wed Aug 21 2019

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN TETON AND
NORTHWESTERN CASCADE COUNTIES UNTIL 730 PM MDT...

At 701 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from 11 miles west of Power to near Fairfield.
Movement was northeast at 20 mph.

Half inch hail and wind gusts up to 50 mph will be possible with
these storms.

Locations impacted include...
Fairfield, Power and Sun River.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

Frequent 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.

These storms 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 4784 11171 4753 11162 4752 11195 4769 11201
TIME...MOT...LOC 0101Z 242DEG 19KT 4769 11192 4756 11190

Moldan