Alert archive / Montana / Severe Thunderstorm Watches in 2012

Severe Thunderstorm Watch 431

June 26, 201210 counties in Montana

The Storm Prediction Center issued this severe thunderstorm watch at Jun 26, 2012, 11:20 AM MDT for 10 counties in Montana. It was in force for 6 hr.

The area

The outline as issued.

The facts

Issued: Jun 26, 2012, 11:20 AM MDT (17:20 UTC)
Expired: Jun 26, 2012, 5:00 PM MDT
In force: 6 hr
Issued by: the Storm Prediction Center
Largest hail expected: 2 in
Strongest gust expected: 60 kt

Counties Blaine County, MT, Cascade County, MT, Chouteau County, MT, Glacier County, MT, Hill County, MT, Lewis and Clark County, MT, Liberty County, MT, Pondera County, MT, Teton County, MT, Toole County, MT

The radar

The Great Falls radar (KTFX), 84 km from the middle of the area, began a volume at 17:24 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

What SPC expected

The probabilities SPC published with the watch, for the watch area over its life.

Two or more tornadoes: 20%
One or more EF2 to EF5 tornadoes: 5%
Ten or more severe wind reports: 40%
One or more gusts of 65 knots or more: 10%
Ten or more severe hail reports: 30%
One or more hailstones of 2 inches or more: 10%
Six or more combined severe hail and wind reports: 60%

Warnings issued inside it

4 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.

Issued	Product	Office	Counties	Lasted
Jun 26, 12:08 PM MDT	Severe Thunderstorm Warning	TFX	Glacier, Pondera, Teton, Toole	67 min
Jun 26, 12:42 PM MDT	Severe Thunderstorm Warning	TFX	Cascade, Chouteau, Teton	63 min
Jun 26, 1:41 PM MDT	Severe Thunderstorm Warning	TFX	Chouteau, Hill	38 min
Jun 26, 2:32 PM MDT	Severe Thunderstorm Warning	TFX	Blaine, Hill	73 min

Discussions around it

SPC mesoscale discussions over the same counties from four hours before the watch to its end.

The nearest sounding before it

Great_falls, MT (KTFX), launched 12:00Z, 5.3 hours before the alert went out and 102 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 1099 J/kg
Mixed-layer CIN: -173 J/kg
Mixed-layer LCL: 763 m above ground
0-6 km bulk shear: 53 kt
0-1 km storm-relative helicity: 223 m²/s²
0-3 km storm-relative helicity: 481 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 20.6

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

615 
WWUS20 KWNS 261720
SEL1  
SPC WW 261720
MTZ000-262300-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 431
NWS STORM PREDICTION CENTER NORMAN OK
1120 AM MDT TUE JUN 26 2012

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF 

       NORTHWEST AND NORTH CENTRAL MONTANA

EFFECTIVE THIS TUESDAY MORNING AND AFTERNOON FROM 1120 AM UNTIL
500 PM MDT.

HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 65
STATUTE MILES EITHER SIDE OF A LINE FROM 70 MILES SOUTH SOUTHWEST
OF CUT BANK MONTANA TO 40 MILES EAST OF HAVRE MONTANA.  FOR A
COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE
UPDATE (WOUS64 KWNS WOU1).

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.

DISCUSSION...STRONG STORMS HAVE DEVELOPED IN A BAND ALONG THE
LEADING EDGE OF INTENSE LARGE SCALE ASCENT ASSOCIATED WITH AN UPPER
SHORT WAVE TROUGH MOVING NEWD ACROSS THE NRN INTERMOUNTAIN REGION. 
STEEP LAPSE RATES AND INCREASING MOISTURE WITH EWD EXTENT WILL
SUPPORT STRONG/SEVERE STORMS WITH POTENTIAL TO PRODUCE LARGE HAIL
AND DAMAGING WINDS.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 450. MEAN STORM
MOTION VECTOR 22035.


...WEISS

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jun 25, 7:12 PM MDT	Mesoscale Discussion	SPC	Blaine, Chouteau, Dawson, Fergus, Garfield, Hill and 11 more	93 min
Jun 25, 10:27 PM MDT	Mesoscale Discussion	SPC	Blaine, Chouteau, Fergus, Garfield, Hill, Liberty and 3 more	93 min
Jun 26, 12:23 AM MDT	Mesoscale Discussion	SPC	Blaine, Chouteau, Hill	67 min
Jun 26, 6:16 AM MDT	Mesoscale Discussion	SPC	Glacier, Hill, Liberty, Pondera, Teton, Toole	89 min
Jun 26, 11:08 AM MDT	Mesoscale Discussion	SPC	Blaine, Cascade, Chouteau, Glacier, Hill, Liberty and 3 more	37 min
Jun 26, 2:06 PM MDT	Mesoscale Discussion	SPC	Daniels, Dawson, Fallon, McCone, Phillips, Prairie and 5 more	54 min
Jun 26, 2:21 PM MDT	Mesoscale Discussion	SPC	Blaine, Cascade, Chouteau, Hill, Lewis and Clark, Liberty and 3 more	54 min

Nearby

Severe Thunderstorm Watches in Montana, 2012 Every severe thunderstorm watch in 2012

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.