Alert archive / Montana / Severe Thunderstorm Warnings in 2011

Severe Thunderstorm Warning 55, NWS Glasgow, MT

July 7, 2011Petroleum County, Montana

NWS Glasgow, MT issued this severe thunderstorm warning at Jul 7, 2011, 9:41 AM MDT for Petroleum County, Montana. It was in force for 64 min. No storm report in the archive falls inside the area while it was in force.

The area

The counties it named.

The facts

Issued: Jul 7, 2011, 9:41 AM MDT (15:41 UTC)
Expired: Jul 7, 2011, 10:45 AM MDT
In force: 64 min
Issued by: NWS Glasgow, MT
Area: Storm-based polygon

County Petroleum County, MT

The nearest sounding before it

Great_falls, MT (KTFX), launched 12:00Z, 3.7 hours before the alert went out and 181 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: 874 J/kg
Mixed-layer CIN: -164 J/kg
Mixed-layer LCL: 1766 m above ground
0-6 km bulk shear: 29 kt
0-1 km storm-relative helicity: 4 m²/s²
0-3 km storm-relative helicity: 55 m²/s²
Significant tornado parameter: 0.0
Supercell composite: -0.1

Open this sounding in Storm Lab

What forecasters said that day

The local office's own words before this severe thunderstorm warning went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Glasgow, MT wrote its last area forecast discussion before this severe thunderstorm warning went out at Jul 7, 2:36 AM MDT, 7 hours 5 minutes earlier.

Area forecast discussion, Jul 7, 2:36 AM MDT, 7 hours 5 minutes before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
236 AM MDT THU JUL 7 2011

.SHORT TERM...FOR NORTHEAST MONTANA...TODAY THROUGH SATURDAY...
THE UPPER LEVEL RIDGE AXIS WILL BE CENTERED OVER EASTERN MONTANA
TODAY. THE NEXT EASTERN PACIFIC UPPER TROUGH/STORM SYSTEM BEGINS
ITS PUSH INTO WESTERN CANADA WHICH AMPLIFIES THE RIDGE TODAY. THE
RESULT WILL BE ANOTHER WARM DAY WITH HIGHS 5*F TO 10*F ABOVE
NORMAL AGAIN. MODERATELY UNSTABLE CONDITIONS WILL DEVELOP TO BE
PRIMED FOR ANY INSTABILITIES THAT WOULD INITIATE AFTERNOON AND
EVENING THUNDERSTORMS. AS THE WESTERN TROUGH DIGS INTO BRITISH
COLUMBIA IT SENDS A COLD FRONT ACROSS THE DIVIDE TONIGHT WHILE
BACKING FLOW ALOFT TO THE SOUTHWEST. SOME LOW LEVEL MOISTURE WILL
INFLOW FROM THE SOUTHEAST WHILE MID-LEVEL MOISTURE FLOWS IN FROM
THE WEST. THE GFS AND NAM DIFFER WITH THE TIMING AND STORM
INITIATION...WHICH COULD BE IN LATE AFTERNOON OR EARLY EVENING.
THE LATER THE FRONTAL PASSAGE OCCURS THE LESS LIKELY FOR ANY STORM
GOING SEVERE TODAY OR THIS EVENING. THE SURFACE TROUGH SLIDES OVER
THE AREA AFTER MIDNIGHT WHICH BRINGS THE BEST CHANCE FOR STORMS
WITH HEAVY RAIN. THEN FRIDAY THE STORM CENTER MOVES OUT OVER THE
CANADIAN PRAIRIE AND STACKS UP. AS IT DOES THE SURFACE TROUGH
MOVES THE REST OF THE WAY THROUGH NEMONT...SPREADING SHOWERS
MAINLY OVER EASTERN ZONES WHERE CONDITIONS WILL BE VERY UNSTABLE
BASED ON LIFTED INDEX NUMBERS AND SURFACE BASED CAPE. THE AREA HAS
BEEN HIGHLIGHTED IN THE SPC CONVECTIVE OUTLOOK FOR SLIGHT RISK FOR
SEVERE THUNDERSTORMS. PRECIPITABLE WATER RANGES FROM A HALF TO
OVER AN INCH. THE MOVEMENT OF THE SURFACE TROUGH WILL BRING WINDY
CONDITIONS TO THE AREA AT TIMES. FRIDAY WILL BE COOLER...CLOSER TO
NORMAL.

FRIDAY NIGHT A SECONDARY FRONTAL BOUNDARY SOUTH OF THE MISSOURI
RIVER WILL INITIATE ADDITIONAL SHOWERS MOSTLY BEFORE MIDNIGHT.
WITH THE LOW CENTER SPINNING IN SASKATCHEWAN THIS BOUNDARY WILL
KEEP THE WARMER AIR TO THE SOUTH FOR SATURDAY KEEPING TEMPERATURES
CLOSE TO NORMAL. SURFACE WINDS AND WINDS ALOFT LINE UP WITH MIXING
TO 700 MB. THIS WILL GENERATE STRONG WESTERLY WINDS SATURDAY. SCT

.LONG TERM...SATURDAY NIGHT THROUGH THURSDAY...
UPPER LOW MOVES FROM SASKATCHEWAN TO MANITOBA SATURDAY NIGHT.
NORTHEAST MONTANA WILL REMAIN MOSTLY DRY AS DRY AIR KEEPS BEING
PULLED ACROSS THE AREA. ON SUNDAY... AN UPPER RIDGE FORMS OVER
THE NORTHERN ROCKIES AND KEEPS THE FORECAST DRY.

MONDAY...THE RIDGE AXIS SHIFTS EAST INTO THE DAKOTAS. THIS WILL
TURN THE FLOW ALOFT OVER EASTERN MONTANA BACK TO THE SOUTHWEST AS
ANOTHER UPPER TROUGH MOVES INTO THE WEST COAST. THIS TROUGH WILL
SEND A FRONTAL BOUNDARY THROUGH EASTERN MONTANA MONDAY AFTERNOON
AND EVENING. CONDITIONS WILL BE UNSTABLE FOR THE COLD FRONT WHICH
SHOULD SET OFF A FEW STRONG THUNDERSTORMS. SOUTHWEST FLOW ALOFT
WILL CONTINUE THROUGH THE REMAINDER OF THE PERIOD WITH THE TROUGH
STAYING OVER THE WEST COAST. WILL KEEP A CHANCE OF THUNDERSTORMS
THROUGH THE REST OF THE PERIOD. FORRESTER

&&

.AVIATION...
VFR CONDITIONS WITH MOSTLY CLEAR SKIES THIS MORNING AND SOME
DAYTIME CUMULUS DEVELOPING THIS AFTERNOON. SCATTERED
THUNDERSTORMS WILL LIKELY DEVELOP ACROSS NORTH CENTRAL MT BY LATE
AFTN AND MAY BE MOVING INTO THE VCNTY OF KGGW AND KOLF AFTER 00Z.
DUE TO UNCERTAINTY IN EXACT TIMING AND LOCATION...WILL ONLY CARRY
A CB MENTION FOR NOW. WINDS WILL BE STRONGEST AT KGGW AND KOLF AFT
18Z THANKS TO TIGHTER PRESSURE GRADIENT THAN FARTHER EAST.

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

WEATHER.GOV/GLASGOW

Hazardous weather outlook, Jul 7, 3:14 AM MDT, 6 hours 27 minutes before

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In the hours before

Special weather statement, Jul 7, 9:20 AM MDT, 21 minutes before

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GLASGOW MT
920 AM MDT THU JUL 7 2011

MTZ021-071545-
PETROLEUM-
920 AM MDT THU JUL 7 2011

THE NATIONAL WEATHER SERVICE IN GLASGOW HAS ISSUED A

SIGNIFICANT WEATHER ADVISORY FOR...
  WESTERN PETROLEUM COUNTY IN NORTHEAST MONTANA...

UNTIL 945 AM MDT.

AT 913 AM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM 14 MILES SOUTHEAST OF ROY...MOVING NORTHEAST AT
30 MPH.

HAIL UP TO THE SIZE OF NICKELS AND WIND GUSTS UP TO 40 MPH ARE
EXPECTED WITH THIS STORM...ALONG WITH FREQUENT DANGEROUS LIGHTNING.

LOCATIONS IN THE ADVISORY INCLUDE...
  RURAL AREAS OF WESTERN PETROLEUM COUNTY...
  RURAL AREAS OF CENTRAL PETROLEUM COUNTY...

THIS STORM MAY INTENSIFY...SO BE CERTAIN TO MONITOR LOCAL RADIO AND
TV STATIONS...AS WELL AS NOAA WEATHER RADIO...FOR ADDITIONAL
INFORMATION AND POSSIBLE WARNINGS FROM THE NATIONAL WEATHER SERVICE.

LAT...LON 4719 10872 4727 10873 4728 10860 4731 10859
      4731 10835 4735 10831 4713 10820 4692 10861
      4709 10862 4709 10871 4710 10875 4718 10875
TIME...MOT...LOC 1519Z 236DEG 25KT 4727 10864

GILCHRIST
WEATHER.GOV/GLASGOW

The office that day

Everything else NWS Glasgow, MT issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 7, 9:20 AM MDT	Special Weather Statement	GGW	Petroleum	25 min
Jul 7, 10:27 AM MDT	Severe Thunderstorm Warning	GGW	Garfield, Petroleum	40 min

Nearby

Severe Thunderstorm Warnings in Montana, 2011 Every severe thunderstorm warning in 2011

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.