Special Weather Statement, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
540 PM MDT Mon Aug 2 2021

...Aviation Section Update...

.SYNOPSIS...

Showers and thunderstorms over Southwestern Montana and portions of
Central Montana are expected to persist into the overnight hours.
Locally heavy rain will continue to be possible with these storms
and could produce flash flooding and debris flows, especially in
recently burn area. After some lingering showers on Tuesday, hot and
dry weather returns for Wednesday and early Thursday. Unsettled
conditions and slightly cooler temperatures can be expected for the
weekend.

&&

.AVIATION...
532 PM MDT Mon Aug 02 2021 (03/00Z TAF period)

Scattered convection across the region should begin to gradually
diminish the first few hours of the 00z TAF period. Have carried
VCSH/VCTS for most aerodromes with KHVR/KLWT having greatest risk
of experiencing convective impacts this evening. Rogue ISO -SHRA
overnight may then occur nearly anywhere. Aside from convective
impacts, VFR to generally prevail through the TAF period. Wind
speeds and directions will vary this evening, generally WSWrly
around 10kts for western aerodromes and ESErly across eastern
aerodromes. Breezy and gusty NWrly winds nearly areawide by
mid/late afternoon Tues.

&&

.PREV DISCUSSION...
/ISSUED 213 PM MDT Mon Aug 2 2021/

Anomalously high levels of monsoon moisture remain in place over
much of the forecast area as a weak shortwave approaches from the
west. Shower and thunderstorm development has already begun over
the southwest and this activity should expand north and eastward
later this afternoon and evening. So far the strongest storms have
occurred in Jefferson county from Boulder to to just southeast of
the Helena valley. These rainfall rates will be common this
afternoon and evening due to the combination of PWAT values being
several standard deviations higher than climatology and relatively
storm motion 10 to 15 mph. It's important to note that the
convective nature of the storms may lead to some areas receiving
very heavy rainfall while others get little to no rain. Anyone
outdoors should be be especially careful as the heavier cells may
cause dangerous mud/debris flows, particularly over any burn scars
or higher and uneven terrain. The current flash flood watch is
handling the situation reasonably well, so no changes will be made
at this time. However, Lewis and Clark County could possibly be
added to the watch area later this afternoon. Showers and storms
will begin to shift eastward and weaken by late this evening, but
expect at least scattered showers and some storms to persist
through Tuesday morning. -RCG

Rain showers may linger during the day on Tuesday, mostly for the
eastern portions of Central Montana. Then a trend toward mostly
dry and warmer conditions is expected through Thursday as an upper
level ridge rebuilds over the Northern Rockies. Unsettled weather
and cooler temperatures return Friday and continue through the
weekend as an upper trough moves from the Pacific Northwest into
the Northern Plains. mpj

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  62  92  57  92 /  80  10   0  10
CTB  60  89  54  87 /  40  10   0  10
HLN  60  93  61  96 /  50  10   0  10
BZN  56  88  53  91 /  80  10   0  10
WYS  46  79  40  82 /  80  10   0  10
DLN  53  85  52  88 /  70   0   0  10
HVR  64  92  59  91 /  40  20  10  10
LWT  62  86  57  88 /  50  50   0  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch until midnight MDT tonight Beaverhead...
Broadwater...Cascade...Gallatin...Jefferson...Madison...Meagher.

&&

http://www.weather.gov/greatfalls

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
612 PM MDT MON AUG 2 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0430 PM     FLASH FLOOD      BOZEMAN                 45.67N 111.04W
08/02/2021                   GALLATIN           MT   PUBLIC

            SEVERAL SOCIAL MEDIA REPORTS OF FLASH
            FLOODING IN DOWNTOWN BOZEMAN. INCLUDING
            SWIFTLY FLOWING WATER FROM SOUTH TO NORTH IN
            THE DOWNTOWN AREA. ADDITIONAL FLOODING
            REPORT FROM SOUTH SIDE OF TOWN NEAR 19TH AND
            GRAF.

&&

HART

Special Weather Statement
National Weather Service Great Falls MT
647 PM MDT Mon Aug 2 2021

MTZ011-013-045-030130-
Chouteau-Liberty-Hill-
647 PM MDT Mon Aug 2 2021

...AN AREA OF STRONG THUNDERSTORMS WILL AFFECT SOUTHEASTERN
LIBERTY...HILL AND NORTHWESTERN CHOUTEAU COUNTIES...

At 646 PM MDT, scattered strong thunderstorms were moving northeast
at 15 mph over portions of Chouteau, Liberty, and Hill Counties.

Periods of heavy rain and winds in excess of 30 mph are possible
with these storms.

Locations impacted include...
Fort Benton, Chester, Inverness, Gildford, Joplin, Carter, Hingham,
Floweree, Rudyard, Loma, Kenilworth, Kremlin and Simpson.

This includes the following highways...
 Highway 2 between mile markers 323 and 374.
 Highway 87 between mile markers 19 and 73.

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with these storms, and may
cause 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.

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 4899 10949 4770 11054 4773 11134 4900 11074
TIME...MOT...LOC 0046Z 215DEG 14KT 4821 11069

SC

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
657 PM MDT MON AUG 2 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0400 PM     HEAVY RAIN       1 SSW BOZEMAN           45.67N 111.05W
08/02/2021  M0.82 INCH       GALLATIN           MT   CO-OP OBSERVER

            BOZEMAN MSU.

&&

SAC

Special Weather Statement
National Weather Service Great Falls MT
739 PM MDT Mon Aug 2 2021

MTZ011-013-044-045-030230-
Chouteau-Liberty-Hill-Toole-
739 PM MDT Mon Aug 2 2021

...AN AREA OF STRONG THUNDERSTORMS WILL AFFECT LIBERTY...EASTERN
TOOLE...WESTERN HILL AND NORTHWESTERN CHOUTEAU COUNTIES...

At 737 PM MDT, scattered strong thunderstorms will continue moving
northeast at 15 mph over portions of Chouteau, Toole, Liberty, and
Hill Counties.

Periods of heavy rain and winds in excess of 30 mph are possible
with this storm.

Locations impacted include...
Chester, Inverness, Lothair, Gildford, Joplin, The Knees, Carter,
Hingham, Rudyard, Tiber Dam, Galata, Whitlash, Devon and Simpson.

This includes the following highways...
 Highway 2 between mile markers 293 and 360.
 Highway 87 between mile markers 23 and 31.

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with these storms, and may
cause 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.

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 4771 11096 4791 11141 4821 11141 4822 11164
      4900 11145 4900 10974
TIME...MOT...LOC 0137Z 212DEG 12KT 4823 11121

SC

Special Weather Statement
National Weather Service Great Falls MT
744 PM MDT Mon Aug 2 2021

MTZ053>055-030230-
Broadwater-Gallatin-Meagher-
744 PM MDT Mon Aug 2 2021

...SCATTERED SHOWERS WITH ISOLATED THUNDERSTORMS WILL AFFECT CENTRAL
BROADWATER...SOUTH CENTRAL MEAGHER AND NORTH CENTRAL GALLATIN
COUNTIES...

At 742 PM MDT, scattered showers with isolated thunderstorms were
located near Toston, or 9 miles southeast of Townsend, moving
northeast at 15 mph.

A period of heavy rain and winds in excess of 30 mph are possible
with these showers and storms.

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

This includes Highway 12 between mile markers 1  and 30, and between
mile markers 77 and 92.

If outdoors, consider seeking shelter inside a building.

Heavy rainfall may cause localized flooding. Do not drive your
vehicle through flooded roadways.

LAT...LON 4604 11128 4618 11162 4657 11141 4636 11087
TIME...MOT...LOC 0142Z 212DEG 12KT 4624 11135

SC

Special Weather Statement
National Weather Service Great Falls MT
747 PM MDT Mon Aug 2 2021

MTZ050-051-054-030230-
Fergus-Judith Basin-Meagher-
747 PM MDT Mon Aug 2 2021

...SCATTERED SHOWERS WITH ISOLATED THUNDERSTORMS WILL AFFECT EAST
CENTRAL MEAGHER...SOUTHEASTERN JUDITH BASIN AND SOUTH CENTRAL FERGUS
COUNTIES...

At 746 PM MDT, scattered showers with isolated thunderstorms were
located 25 miles southwest of Hobson, or 26 miles northwest of
Harlowton, moving northeast at 5 mph.

A period of heavy rain and winds in excess of 30 mph are possible
with these showers and storms.

Locations impacted include...
Ackley Lake State Park, Sapphire Village, Utica, Buffalo, Garneill
and Windham.

This includes the following highways...
 Highway 200 between mile markers 42 and 43.
 Highway 12 between mile markers 73 and 77.

If outdoors, consider seeking shelter inside a building.

Heavy rainfall may cause localized flooding. Do not drive your
vehicle through flooded roadways.

LAT...LON 4669 10959 4670 10982 4675 10996 4674 11003
      4675 11005 4671 11015 4672 11027 4645 11028
      4666 11063 4710 11018 4672 10950
TIME...MOT...LOC 0146Z 217DEG 5KT 4672 11023

SC