A very unstable atmosphere and strong shear interacted with an upper-level disturbance to produce morning, afternoon, and evening periods of severe thunderstorms.
Every event with a place to put it. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS GGW wrote it up.
A very unstable atmosphere and strong shear interacted with an upper-level disturbance to produce morning, afternoon, and evening periods of severe thunderstorms.
The local office's own words before the first event, 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 the first event at Aug 30, 8:07 PM MST, 6 hours 8 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GLASGOW MT 907 PM MDT TUE AUG 30 2011 .SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH THURSDAY... UPDATE...STORMS HAVE BEEN FIRING ALONG FRONTAL BOUNDARY ACROSS CENTRAL MONTANA AND SW SASKATCHEWAN THIS EVENING. WITH SOUTHWEST FLOW ALOFT OVER MONTANA AT THIS TIME THE FRONT WILL BE SLOW TO MOVE EAST OVERNIGHT. THE SE ZONES SHOULD STAY DRY OVERNIGHT. A FEW OF THESE STORMS MAY FIND THEIR WAY INTO THE NORTHERN AND WESTERN ZONES OF THE FORECAST AREA OVERNIGHT. WILL MAINTAIN A SLIGHT CHANCE FOR NOW. REDUCED CLOUD COVER IN THE SE TO MOSTLY CLEAR IN THE UPDATE. FORRESTER PREVIOUS SHORT TERM... A LONG WAVE UPPER LEVEL TROUGH MOVING INTO THE WEST WILL NUDGE A COLD FRONT INTO NORTH CENTRAL AND EASTERN MONTANA TONIGHT...SO WILL MAINTAIN CHANCE POPS FOR RAIN SHOWERS AND THUNDERSTORMS OVERNIGHT. BY WEDNESDAY MORNING THE COLD FRONT WILL BEGIN ITS PUSH ACROSS NORTHEAST MONTANA. BEFORE THE FRONT GETS HERE...A LEE SURFACE TROUGH SETTLES OVER THE AREA WHICH INCREASES INSTABILITY. LATEST GUIDANCE SUGGEST CAPE OF AROUND 1500 J/KG WAITING FOR THE FRONT WHICH WILL BREAK THE INVERSION CAP. IN ADDITION VERTICAL SHEAR WILL SUPPORT DEVELOPMENT OF STORMS. EXPECT SOME VIGOROUS STORMS WITH HAILS AND STRONG WINDS...ALONG WITH SIGNIFICANT RAIN UNDER AND BEHIND THE FRONT. HIGH POPS WEDNESDAY NIGHT STILL LOOK GOOD FOR POST FRONTAL RAIN. BUT INVERTED SURFACE TROUGH SHOULD PUSH THE BULK OF PRECIPITATION NORTH INTO CANADA. ADDED POSSIBLE SEVERE WORDING TO WX WHICH IS SUPPORTED BY THE SPC CONVECTIVE OUTLOOK FOR DAY 2 WHERE THEY PLACED MOST OF NORTHEAST MONTANA UNDER A SLIGHT RISK FOR SEVERE THUNDERSTORMS. LATE WEDNESDAY NIGHT WITH THE FRONT HAVING MOVED ON INTO NORTH DAKOTA...SHOWERS SHOULD DIMINISH RAPIDLY. A SIGNIFICANT FEATURE OF THE FRONT IS THE COOL AIR BEHIND IT. AFTER THE TROUGH SLIDES ACROSS THE ZONES THURSDAY...FLOW ALOFT VEERS TO THE NORTHWEST. EXPECT TEMPERATURES TO BEGIN TO TREND LOWER...TO AROUND 15*F LOWER THAN TEMPERATURES ON WEDNESDAY. SCT .LONG TERM...THURSDAY NIGHT THROUGH TUESDAY... VERY FEW CHANGES AGAIN TO THE LONG TERM...WITH A FEW SHORTWAVES AFFECTING THE AREA LEADING INTO THE WEEKEND AND UPPER RIDGING BUILDING IN THEREAFTER. THE ECMWF AND GFS SEEM TO BE HINTING THAT UPPER RIDGING NEXT WEEK MAY BECOME MORE AMPLIFIED AND MAY RAISE HIGH TEMPS UP A BIT. SOME MINOR TWEAKS HERE AND THERE TO TEMPERATURES WINDS AND POPS TO MATCH GUIDANCE CONSENSUS...OTHERWISE THE FORECAST APPEARS ON TRACK. ONE CHANGE TO NOTE...POPS WERE DROPPED SLIGHTLY FOR THE 06Z FRIDAY THROUGH 00Z SATURDAY TIMEFRAME. IN BETWEEN SHORTWAVES...IT APPEARS AS BRIEF UPPER RIDGING WILL CREATE DRIER CONDITIONS FOR THE REGION AS SUGGESTED BY THE ECMWF AND GFS. THE PREVIOUS DISCUSSION DID NOTE THAT THE SECOND WAVE WILL HAVE LESS MOISTURE...BUT KEPT POPS IN MOSTLY FOR THE NORTHERN ZONES AS GUIDANCE SUGGESTS THAT THESE AREAS WILL HAVE THE GREATEST CHANCE FOR PRECIP. AFTER THE RIDGE MOVES IN...DRY CONDITIONS WILL PREVAIL ALONG WITH STEADILY INCREASING TEMPERATURES INTO NEXT WEEK. BARNWELL PREVIOUS LONG TERM DISCUSSION...THE LONG TERM BEGINS AS A SHORTWAVE EXITS THE REGION THURSDAY NIGHT AND MOVES INTO NORTH DAKOTA. THINGS WILL DRY OUT FOR A BRIEF PERIOD OF TIME UNTIL FRIDAY AFTERNOON WHEN ANOTHER SHORTWAVE COLD FRONT COMBO SLIDES SOUTHEASTWARD OUT OF SASKATCHEWAN AND CLIPS NORTHEAST MONTANA. MOISTURE WILL BE LIMITED WITH THIS WAVE BUT WILL LEAVE A SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS NORTH OF THE MISSOURI RIVER. I EXPECT ANY MOISTURE WITH THIS SYSTEM TO REMAIN ACROSS THE NORTHERN ZONES SO I LEFT THE SOUTHERN ZONES DRY. FRIDAY NIGHT THE SHORTWAVE WILL EXIT TO THE EAST AND FROM THAT POINT ON EASTERN MONTANA WILL DRY OUT AND THINGS SHOULD REMAIN DRY THROUGH THE MIDDLE OF NEXT WEEK. TEMPERATURES WILL BE COOL ON FRIDAY AND SATURDAY. THINK UPPER 60S TO THE MID 70S ACROSS MOST OF THE REGION...WHICH IS BELOW CLIMATOLOGY. AN UPPER RIDGE BEGINS TO BUILD INTO WESTERN MONTANA LATE ON SATURDAY WHICH WILL RETURN THE TEMPERATURES BACK TO CLIMATOLOGY OR SLIGHTLY ABOVE CLIMO FOR THE BEGINNING OF NEXT WEEK. RSMITH && .AVIATION... EXPECT VFR CONDITIONS FOR THE REGION INTO THE OVERNIGHT AND EARLY MORNING HOURS. DURING THE DAY ON WEDNESDAY...A CHANCE FOR SHOWERS AND THUNDERSTORMS WILL MOVE IN TO THE REGION. BRIEF PERIODS OF MVFR OR IFR CONDITIONS MAY POP UP...DEPENDING ON THE STRENGTH OF THE STORMS. OTHERWISE...EXPECT WINDS AROUND 5 TO 12 MPH OUT OF THE EAST AND SOUTHEAST BEFORE YET ANOTHER FRONTAL PASSAGE LATE WEDNESDAY EVENING INTO THURSDAY. BARNWELL && .GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE. && WEATHER.GOV/GLASGOW
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GLASGOW MT
1228 AM MDT WED AUG 31 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1150 PM TSTM WND GST WINNETT 47.00N 108.35W
08/30/2011 E41 MPH PETROLEUM MT MESONET
&&
METZGERSPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GLASGOW MT
1252 AM MDT WED AUG 31 2011
MTZ016-017-022-310745-
GARFIELD-PHILLIPS-VALLEY-
1252 AM MDT WED AUG 31 2011
THE NATIONAL WEATHER SERVICE IN GLASGOW HAS ISSUED A
SIGNIFICANT WEATHER ADVISORY FOR...
SOUTHWESTERN VALLEY COUNTY IN NORTHEAST MONTANA...
SOUTHERN PHILLIPS COUNTY IN NORTHEAST MONTANA...
NORTHERN GARFIELD COUNTY IN NORTHEAST MONTANA...
UNTIL 145 AM MDT.
AT 1248 AM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM DODSON TO 14 MILES
NORTHEAST OF DEVILS CREEK REC AREA TO 7 MILES WEST OF BRUSETT...AND
MOVING EAST AT 35 MPH.
WIND GUSTS UP TO 50 MPH ARE EXPECTED WITH THESE STORMS...ALONG WITH
FREQUENT DANGEROUS LIGHTNING. WIND GUSTS OF 45 MPH HAVE BEEN
REPORTED IN NORTHERN PETROLEUM COUNTY.
LOCATIONS IN THE ADVISORY INCLUDE...
BRUSETT...
MALTA...
HELL CREEK REC AREA...
SACO...
THIS STORM MAY INTENSIFY...SO BE CERTAIN TO MONITOR LOCAL RADIO AND
TV STATIONS...AS WELL AS LOCAL CABLE TV OUTLETS...FOR ADDITIONAL
INFORMATION AND POSSIBLE WARNINGS FROM THE NATIONAL WEATHER SERVICE.
LAT...LON 4856 10712 4782 10634 4731 10644 4733 10718
4851 10835
TIME...MOT...LOC 0650Z 269DEG 30KT 4844 10815 4778 10745
4740 10738
METZGER/PROTON
WEATHER.GOV/GLASGOWPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GLASGOW MT
103 AM MDT WED AUG 31 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1230 AM TSTM WND GST 35 SW MALTA 48.00N 108.41W
08/31/2011 M51 MPH PHILLIPS MT MESONET
&&
METZGERSPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GLASGOW MT
146 AM MDT WED AUG 31 2011
MTZ016-017-022-023-059-061-310845-
GARFIELD-MCCONE-PHILLIPS-VALLEY-
146 AM MDT WED AUG 31 2011
THE NATIONAL WEATHER SERVICE IN GLASGOW HAS ISSUED A
SIGNIFICANT WEATHER ADVISORY FOR...
VALLEY COUNTY IN NORTHEAST MONTANA...
EASTERN PHILLIPS COUNTY IN NORTHEAST MONTANA...
WESTERN MCCONE COUNTY IN NORTHEAST MONTANA...
NORTHEASTERN GARFIELD COUNTY IN NORTHEAST MONTANA...
UNTIL 245 AM MDT.
AT 139 AM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM 12 MILES NORTHWEST
OF SACO TO 9 MILES WEST OF DUCK CREEK REC AREA TO 10 MILES EAST OF
JORDAN...AND MOVING EAST AT 35 MPH.
HAIL UP TO ONE-HALF INCH IN DIAMETER AND WIND GUSTS UP TO 50 MPH
HAVE BEEN REPORTED WITH THESE STORMS...ALONG WITH FREQUENT DANGEROUS
LIGHTNING.
LOCATIONS IN THE ADVISORY INCLUDE...
HINSDALE...
DUCK CREEK REC AREA...
FORT PECK... GLASGOW AND TAMPICO...
GLASGOW...
ROCK CREEK REC AREA...
FORT PECK LAKE...
NASHUA...
SAINT MARIE...
THIS STORM MAY INTENSIFY...SO BE CERTAIN TO MONITOR LOCAL RADIO AND
TV STATIONS...AS WELL AS LOCAL CABLE TV OUTLETS...FOR ADDITIONAL
INFORMATION AND POSSIBLE WARNINGS FROM THE NATIONAL WEATHER SERVICE.
LAT...LON 4806 10584 4802 10584 4803 10580 4798 10574
4725 10575 4725 10679 4798 10680 4867 10767
4867 10660
TIME...MOT...LOC 0743Z 270DEG 29KT 4860 10744 4798 10666
4734 10665
METZGER/PROTON
WEATHER.GOV/GLASGOWPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GLASGOW MT
229 AM MDT WED AUG 31 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0125 AM TSTM WND GST 7 SE DEVILS CREEK RECRE 47.56N 107.53W
08/31/2011 M42 MPH GARFIELD MT MESONET
&&
METZGERSPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GLASGOW MT
253 AM MDT WED AUG 31 2011
MTZ018-061-311000-
DANIELS-VALLEY-
253 AM MDT WED AUG 31 2011
THE NATIONAL WEATHER SERVICE IN GLASGOW HAS ISSUED A
SIGNIFICANT WEATHER ADVISORY FOR...
NORTHERN VALLEY COUNTY IN NORTHEAST MONTANA...
NORTHWESTERN DANIELS COUNTY IN NORTHEAST MONTANA...
UNTIL 400 AM MDT.
AT 250 AM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM 13 MILES SOUTHWEST OF OPHEIM...MOVING NORTHEAST
AT 45 MPH.
HAIL UP TO ONE-HALF INCH IN DIAMETER AND WIND GUSTS UP TO 40 MPH ARE
EXPECTED WITH THIS STORM...ALONG WITH FREQUENT DANGEROUS LIGHTNING.
LOCATIONS IN THE ADVISORY INCLUDE...
RICHLAND...
PEERLESS...
THIS STORM MAY INTENSIFY...SO BE CERTAIN TO MONITOR LOCAL RADIO AND
TV STATIONS...AS WELL AS LOCAL CABLE TV OUTLETS...FOR ADDITIONAL
INFORMATION AND POSSIBLE WARNINGS FROM THE NATIONAL WEATHER SERVICE.
LAT...LON 4885 10545 4857 10656 4858 10663 4872 10673
4901 10589 4900 10555
TIME...MOT...LOC 0853Z 245DEG 41KT 4870 10648
METZGER/PROTON
WEATHER.GOV/GLASGOWThe Glasgow radar (KGGW), 66 km away, was scanning. The volume nearest the first event began at 09:14 UTC.
10 thunderstorm wind, 5 hail. Local standard time, as filed.
Public reported a 60-foot radio tower bent in half and 4-inch diameter tree limbs broken. Wind gusts of 85 mph estimated from EF-scale toolkit.
Glasgow ASOS measured a 61 mph wind gust.
Mesonet measured a 66 mph wind gust.
Observer also measured sustained winds between 40 and 60 mph.
Spotter measured a 71 mph wind gust.
Spotter reported penny- to nickel-sized hail stones.
Spotter estimated 60 mph wind gusts and reported pea-sized hail stones.
Spotter estimated 70 to 80 mph wind gusts.
Spotter reported slushy penny-sized stones.
Spotter estimated wind gusts of 70 mph.
Spotter reported small amounts of penny-sized hail stones.
ASOS measured sustained winds at 44 mph with a gust of 58 mph.
Storm chaser reported quarter-sized hail mixed with heavy rain.
Public estimated penny-sized hail stones.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2011Every state in 2011This day in weather historyWarnings in Montana, August 2011
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 349535, 346226, 346227, 346231, 346232, 346933, 346233, 346234, 346935, 346235, 346936, 346236, 346237, 346224, 346225.