Severe Thunderstorm Warning 9, NWS Missoula, MT

994 
WWUS55 KMSO 292220
SVSMSO

Severe Weather Statement
National Weather Service Missoula MT
420 PM MDT Tue Aug 29 2023

MTC061-089-292230-
/O.CON.KMSO.SV.W.0009.000000T0000Z-230829T2230Z/
Mineral MT-Sanders MT-
420 PM MDT Tue Aug 29 2023

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 430 PM MDT
FOR NORTH CENTRAL MINERAL AND CENTRAL SANDERS COUNTIES...

At 419 PM MDT, a severe thunderstorm was located near St. Regis, or
17 miles northwest of Superior, moving north at 30 mph.

HAZARD...60 mph wind gusts and penny size hail.

SOURCE...Radar indicated.

IMPACT...Expect damage to roofs, siding, and trees.

Locations impacted include...
De Borgia and St. Regis. 

PRECAUTIONARY/PREPAREDNESS ACTIONS...

For your protection move to an interior room on the lowest floor of a
building.

&&

LAT...LON 4748 11535 4742 11496 4724 11506 4723 11512
      4725 11524 4733 11537
TIME...MOT...LOC 2219Z 193DEG 27KT 4735 11519 

HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...0.75 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...60 MPH

$$

534 
WWUS55 KMSO 292227
SVSMSO

Severe Weather Statement
National Weather Service Missoula MT
427 PM MDT Tue Aug 29 2023

MTC061-089-292236-
/O.EXP.KMSO.SV.W.0009.000000T0000Z-230829T2230Z/
Mineral MT-Sanders MT-
427 PM MDT Tue Aug 29 2023

...THE SEVERE THUNDERSTORM WARNING FOR NORTH CENTRAL MINERAL AND
CENTRAL SANDERS COUNTIES WILL EXPIRE AT 430 PM MDT...
        
The storm which prompted the warning has moved out of the area.
Therefore, the warning will be allowed to expire.  However, gusty
winds are still possible with this thunderstorm.

LAT...LON 4748 11535 4742 11496 4724 11506 4723 11512
      4725 11524 4733 11537
TIME...MOT...LOC 2226Z 193DEG 27KT 4740 11517 

$$

Area Forecast Discussion
National Weather Service Missoula MT
256 AM MDT Tue Aug 29 2023

...STRONG THUNDERSTORMS WITH LOCALIZED DAMAGING WINDS TUESDAY
AFTERNOON AND EVENING...
...WIDESPREAD RAIN ACROSS NORTHWEST MONTANA THROUGH WEDNESDAY...

.DISCUSSION...
A pacific storm system remains on track to impact the area later
today through Wednesday. This multifaceted system will bring
strong thunderstorms, with outflow winds, followed by widespread
rainfall and cooler temperatures.

*Thunderstorm Threats: As the pacific trough moves into eastern
 Oregon and Washington this afternoon, atmospheric moisture and
 instability will increase. Ensemble guidance continues to show
 the deepest instability across Idaho and Clearwater Counties,
 where the HREF has 750-1000 J/kg of MUCAPE. Thunderstorms will
 develop between 100-200pm PDT and will quickly increase in
 coverage thereafter. Wind shear will increase into the 40-50kt
 range as an upper level jet streak moves overhead as the trough
 moves across northeast Oregon. High resolution models suggest
 discrete cells will develop initially ahead of the cold front,
 before transitioning into linear modes as they move into western
 Montana. The environment will support isolated (5% probability)
 severe hail and wind across Idaho and Clearwater Counties. As
 thunderstorms move into western Montana, damaging outflow winds
 become the primary concern. Forecast soundings show a classic
 inverted-V profile, with significant DCAPE values in excess of
 1000 J/kg, which increases confidence for strong outflow winds.
 Thunderstorms will track across Mineral, Sanders, Missoula, and
 Ravalli Counties between 300-600pm MDT, reaching northwest
 Montana and areas along the divide between 500-1000pm MDT. The
 US-93 corridor generally has the highest threat for outflow
 winds, as the HREF has a 90% probability for winds in excess of
 35 mph. Individual model runs continue to show localized areas of
 50-70 mph wind gusts, associated with the strongest cells. Now
 is the time to prepare for potential impacts. Consider moving
 vehicles away from trees and be ready for areas of power outages.

*Rain: The trough will deepen and close off as it tracks over the
 Glacier Park region Tuesday night into Wednesday. High
 atmospheric moisture and synoptic forcing will lead to prolonged
 period of rain, with the highest rainfall amounts across Flathead
 and Lincoln Counties. Ensemble model means have trended wetter
 across northwest Montana and have come into better alignment with
 the placement of the upper level low. The heaviest rainfall
 totals (1.50-3.00”) will focus across the Whitefish and Swan
 Ranges and in Glacier Park. A favorable set up exists for
 enhanced rainfall rates, as shallow instability (25-50 J/kg) is
 released through orographic lift. Our updated forecast matches
 closely with HREF and UW WRF ensemble means; however, it is worth
 mentioning that the high end scenario (90th percentile), would
 point towards rain totals closer to 3.50-5.00 inches across these
 mountain ranges.

Temperatures will cool 20-30 degrees behind the front Wednesday.
A tightening pressure gradient will also lead to an increase in
westerly winds. The highest winds will focus across west-central
and southwest Montana, where frequent gusts of 20-35 mph are
expected.

A closed low will dig southward across Oregon and northern
California Thursday into the weekend. A southerly flow pattern
will take shape across the Northern Rockies, keeping shower and
thunderstorm chances in the forecast. /Lukinbeal

&&

.AVIATION...A significant change is expected this afternoon and
evening as a pacific trough and cold front moves through the
Northern Rockies. Strong to potentially severe thunderstorms will
develop along and ahead of the cold front across Idaho and
Clearwater Counties between 29/1900-2100Z and will track north and
east into western Montana thereafter. Atmospheric instability and
wind shear will support the risk for large hail and outflow winds
across Idaho, with outflow winds being the primary concern in
Montana. All terminals will be at risk for outflow wind gusts
between 30-50 kts from any storms in the vicinity. There is a 90
percent probability for outflow winds in excess of 30kts in the
vicinity of KMSO, KHRF, KSMN between 29/2100Z - 30/0300Z and near
KBTM between 30/0200-0600Z. /Lukinbeal

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Wind Advisory from 3 PM this afternoon to 8 PM MDT this evening
     for Flathead/Mission Valleys.

ID...None.
&&

Special Weather Statement
National Weather Service Missoula MT
202 PM PDT Tue Aug 29 2023

IDZ006-292145-
Southern Clearwater Mountains ID-
202 PM PDT Tue Aug 29 2023

...A strong thunderstorm will impact portions of southeastern Idaho
County through 245 PM PDT...

At 201 PM PDT, Doppler radar was tracking a strong thunderstorm 44
miles northeast of McCall, moving 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...
Dixie, Red River Hot Spring, Warren, Orogrande, Elk City, and Mackay
Bar.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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.

A Severe Thunderstorm Watch remains in effect until 800 PM PDT for
central Idaho.

&&

LAT...LON 4595 11556 4588 11471 4520 11521 4520 11571
TIME...MOT...LOC 2101Z 203DEG 37KT 4525 11533

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

Special Weather Statement
National Weather Service Missoula MT
315 PM MDT Tue Aug 29 2023

MTZ006-007-292200-
Bitterroot/Sapphire Mountains MT-Butte/Blackfoot Region MT-
315 PM MDT Tue Aug 29 2023

...Strong thunderstorms will impact portions of Deer Lodge,
southeastern Granite, east central Ravalli, northwestern Silver Bow
and south central Powell Counties through 400 PM MDT...

At 314 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from near Anaconda to 22 miles north of Wisdom.
Movement was north at 35 mph.

HAZARD...Winds in excess of 40 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...
Deer Lodge, Anaconda, Philipsburg, West Valley, Warm Springs, Galen,
Porters Corner, Lost Creek, Opportunity, Racetrack, and Georgetown.

This includes Interstate 90 between mile markers 177 and 207.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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.

A Severe Thunderstorm Watch remains in effect until 900 PM MDT for
west central Montana.

&&

LAT...LON 4609 11278 4589 11347 4593 11349 4594 11351
      4591 11354 4588 11353 4587 11358 4585 11360
      4584 11362 4628 11349 4655 11258
TIME...MOT...LOC 2114Z 198DEG 32KT 4612 11286 4593 11351

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH