Severe Thunderstorm Warning 38, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
549 PM MDT Sun Jul 3 2022

...Aviation Section Updated...

.SYNOPSIS...

A series of weather disturbances will bring several waves of
showers and thunderstorms to the Northern Rockies through early
this week. Severe thunderstorms are possible this afternoon and
evening across parts of central and southwest Montana with
potential for damaging winds and hail. Temperatures trend cooler
today and Monday, especially over western portions of north-
central Montana, before a warming trend commences mid to late
this week.

&&

.DISCUSSION...

There is not much change to the forecast for the next 7 days. The
severe weather threat appears to be materializing as forecast,
with the greatest threat over much of southwest Montana,
especially around the Bozeman area, extending north and northeast
through Meagher and east into Judith Basin and Fergus Counties.
Please see SPC Mesoscale Convective Discussion #1338 for an in-
depth discussion on the developing situation over this region. A
Severe Thunderstorm Watch is in effect for southwest Montana for
this afternoon and extends into central Montana late this
afternoon into early this evening.

Upper level low/trough offshore of the west coast continues to
gradually edge east toward the coast while broad ridging across the
central US attempts to expand to the W and NW keeping an
anticyclonic SW flow in place across MT through the next several
days while several pieces of shortwave energy eject out of the
western trough up and across the Northern Rockies and MT. Several
areas of showers and some embedded weak thunderstorms continue to
lift NE/E across the forecast area this morning and early
afternoon. Precipitation rates have been over 0.25"/hr across
parts of the region, especially northwest of Great Falls towards
the Cut Bank area.

The Great Basin disturbance lifts N/NE across the region this
afternoon, providing the larger scale lift for a good coverage of
showers and thunderstorms, some of which may be severe,
particularly across eastern portions of SW and central MT.
Greatest instability (MUCAPE 1000-2000 J/kg) is likely to develop
east of a line from Dillon to White Sulphur Springs to Lewistown
with some uncertainty in the NW extent. Mid-level wind speed
maximum associated with the wave lifting out of NV will bring
sufficient shear to support organized thunderstorms with the most
likely scenario seeing storms organize into one or several
clusters moving NE/E across Madison, Gallatin, Broadwater,
Meagher, Judith Basin and Fergus counties this afternoon through
early this evening. Primary concern is damaging winds in excess of
60 mph, which could be on a more widespread scale with potential
for linear organization of storms and bowing. Large hail is also a
threat with organized updrafts, especially earlier in the mid
afternoon period. Showers and storms will also spread north across
the rest of north-central MT this afternoon and evening with
lower potential for strong winds/hail from Great Falls to Havre
and NW, but deep moisture and larger scale lift will bring the
potential for localized heavy rain.

Additional disturbances lifting out of the west coast trough and
across the area Monday and Tuesday will bring similar results with
additional rounds of showers and thunderstorms and some risk for
strong to isolated severe storms both days in the afternoon/evening
periods. Instability and wind shear is likely to be weaker than what
is anticipated today, so coverage and intensity of storms Mon/Tues
will likely be less as well.

Looking ahead, ensemble model guidance shows the upper level ridge
currently centered over the S-Central US making some progress to the
west mid-late this week, which will bring some warming to the
region, especially by Friday and Saturday. Residual moisture in place
across the region with subtle disturbances still likely to be
embedded in the SW flow around the NW periphery of the ridge will
keep at least a slight chance for some daily thunderstorm development
through the upcoming week. Hoenisch

&&

.AVIATION...
549 PM MDT Sun Jul 3 2022 (04/00Z TAF period)

The chance of severe thunderstorms will wind down through the early
to mid-evening. However, additional rounds of showers and
thunderstorms will move across the region through the overnight,
with showers and thunderstorms impacting KHLN, KBZN, KEKS to begin
the TAF period, and with VCSH or VCTS at the remaining terminals
with the exception of KCTB, where IFR cigs and fog have developed
and are likely to continue into the late morning Monday. MVFR cigs
will also likely return to KHVR, KGTF, KLWT, and possibly KHLN late
this evening or later in the overnight tonight. Yet another chance
of afternoon and evening showers and thunderstorms develop Monday
for most of the terminals.

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  53  73  51  77 /  70  60  60  40
CTB  51  67  48  73 /  80  60  50  30
HLN  56  77  56  80 /  70  70  40  40
BZN  52  81  51  82 /  50  50  30  50
WYS  44  73  40  77 /  30  10  10  20
DLN  49  77  49  77 /  40  30  10  40
HVR  57  73  54  77 /  90  50  50  40
LWT  52  73  51  74 /  80  70  70  60

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Severe Thunderstorm Watch in effect until 8 PM MDT this evening
Beaverhead...Madison...Gallatin...Jefferson...Meagher...Judith
Basin...Fergus.

&&

http://www.weather.gov/greatfalls

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Special Weather Statement
National Weather Service Great Falls MT
526 PM MDT Sun Jul 3 2022

MTZ015-040015-
Madison MT-
526 PM MDT Sun Jul 3 2022

...Strong thunderstorms will impact portions of Madison County
through 615 PM MDT...

At 525 PM MDT, Doppler radar was tracking an area of strong
thunderstorms along and northeast of a line extending from 20 miles
southeast of Dillon to 26 miles north of Monida. Movement was
northeast at 40 mph.

HAZARD...Winds in excess of 30 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Virginia City, Ennis, Alder, Pony, Norris, Mcallister, Jeffers,
Laurin and Cameron.

This includes Highway 287 between mile markers 27 and 66.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

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

A Severe Thunderstorm Watch remains in effect until 800 PM MDT for
south central and southwestern Montana.

&&

LAT...LON 4487 11217 4499 11219 4500 11233 4509 11234
      4509 11245 4514 11246 4570 11191 4539 11135
      4536 11135 4535 11138 4515 11138 4484 11210
TIME...MOT...LOC 2325Z 234DEG 37KT 4500 11234 4491 11211

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...30 MPH

ML

Special Weather Statement
National Weather Service Great Falls MT
600 PM MDT Sun Jul 3 2022

MTZ014-048-040100-
Southern Rocky Mountain Front MT-
Central and Southern Lewis and Clark MT-
600 PM MDT Sun Jul 3 2022

...Strong thunderstorms will impact portions of southern Lewis and
Clark, northern Broadwater Counties through 700 PM MDT...

At 558 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from 14 miles south of Lincoln to 14 miles north of
Basin. Movement was northeast at 20 mph.

HAZARD...Winds in excess of 30 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Helena, Lincoln, East Helena, Wolf Creek, Marysville, York, Rimini,
Spring Meadow Lake State Park, Canyon Creek, Black Sandy State Park,
Austin and Bean Lake.

This includes the following highways...
 Interstate 15 between mile markers 191 and 232.
 Highway 12 between mile markers 28 and 54.

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.

If on or near Upper and Lower Holter or Hauser Lakes, 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.

A Severe Thunderstorm Watch remains in effect until 800 PM MDT for
southwestern Montana.

&&

LAT...LON 4718 11280 4736 11235 4676 11161 4674 11164
      4657 11165 4657 11202 4652 11207 4650 11220
      4646 11217 4642 11226 4642 11232 4665 11231
      4666 11241 4670 11242 4670 11253 4683 11253
      4684 11280
TIME...MOT...LOC 2358Z 243DEG 18KT 4675 11275 4647 11236

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...30 MPH

RCG

Special Weather Statement
National Weather Service Great Falls MT
604 PM MDT Sun Jul 3 2022

MTZ014-048-040100-
Southern Rocky Mountain Front MT-
Central and Southern Lewis and Clark MT-
604 PM MDT Sun Jul 3 2022

...Strong thunderstorms will impact portions of southern Lewis and
Clark County through 700 PM MDT...

At 558 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from 14 miles south of Lincoln to 14 miles north of
Basin. Movement was northeast at 20 mph.

HAZARD...Winds in excess of 30 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Helena, Lincoln, East Helena, Wolf Creek, Marysville, York, Rimini,
Spring Meadow Lake State Park, Canyon Creek, Black Sandy State Park,
Austin and Bean Lake.

This includes the following highways...
 Interstate 15 between mile markers 191 and 232.
 Highway 12 between mile markers 28 and 54.

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.

If on or near Upper and Lower Holter or Hauser Lakes, 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.

A Severe Thunderstorm Watch remains in effect until 800 PM MDT for
southwestern Montana.

&&

LAT...LON 4718 11280 4736 11235 4676 11161 4674 11164
      4657 11165 4657 11202 4652 11207 4650 11220
      4646 11217 4642 11226 4642 11232 4665 11231
      4666 11241 4670 11242 4670 11253 4683 11253
      4684 11280
TIME...MOT...LOC 2358Z 243DEG 18KT 4675 11275 4647 11236

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...30 MPH

RCG