A developing surface low pressure over eastern Montana helped to pull a warm and unstable airmass into the region from the south by the afternoon. An upper trough moving toward the area from the Pacific Northwest provided an extra contributor to the development of the 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 developing surface low pressure over eastern Montana helped to pull a warm and unstable airmass into the region from the south by the afternoon. An upper trough moving toward the area from the Pacific Northwest provided an extra contributor to the development of the thunderstorms. The thunderstorms were only observed to be severe within a small area in Valley County.
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 May 19, 6:48 PM MST, 1 hour 15 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GLASGOW MT 748 PM MDT TUE MAY 19 2009 .SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH THURSDAY... OVERALL FLAVOR OF THE FORECAST WELL ON TRACK WITH COLD FRONT SCHEDULED TO SWOOP THRU LATER THIS EVENING AND TONIGHT. IN ADVANCE SOME SHOWERS AND THUNDERSTORMS ARE AFFECTING PARTS OF THE CWA. MAIN THRUST OF THE EVENING UPDATE WAS TO REARRANGE POPS A BIT FOR THIS EVENING TO BETTER ACCOUNT FOR CURRENT ACTIVITY. WIND HAS DROPPED BELOW ADVISORY CRITERIA ACROSS FORT PECK LAKE...THEREFORE THE ADVISORY WAS ALLOWED TO EXPIRE AT 6 PM. WHEN THE FRONT MOVES ACROSS THE LAKE TONIGHT WIND MAY AGAIN APPROACH CRITERIA...BUT THINKING FOR NOW IS IT WILL FALL JUST A BIT SHORT. DID NOT FEEL THE NEED TO MESS MUCH WITH TEMPERATURES OR SKY COVER AS THEY LOOKED ABOUT RIGHT. PREVIOUS DISCUSSION... PASSAGE OF AN UPPER LEVEL TROUGH SHOULD HELP TO KICK-OFF SHOWERS AND A FEW THUNDERSTORMS THIS AFTERNOON...CONTINUING OVERNIGHT. MOST LIKELY AREAS FOR INITIAL PRECIPITATION THIS AFTERNOON IS WEST OF GLASGOW WITH SHOWERS MOVING EASTWARD OFF OF HIGHER TERRAIN...AND TO THE SOUTH AND SOUTHWEST ALONG A WARM FRONT. SOUTH OF THE WARM FRONT IS ALSO AN AREA OF HIGHER INSTABILITY. IF NOTHING INITIATES THIS AFTERNOON...SHOWERS SHOULD STILL OCCUR OVERNIGHT AS A COLD FRONT IS DRAWN THROUGH THE AREA. A SECOND BOUNDARY PASSES THROUGH THE AREA WEDNESDAY MORNING WHICH ALSO CARRIES A CHANCE OF SHOWERS WITH IT. WIND PICKS-UP AGAIN WEDNESDAY. WINDS ALOFT ARE QUITE STRONG WITH THE UPPER LEVEL STORM TOPPING 90 KTS AT 400 MB. CLOSER TO THE SURFACE...25 TO 35 KTS ARE AVAILABLE TO BE MIXED TO THE SURFACE. BY THURSDAY CHANCES OF PRECIPITATION DECLINE AS WELL AS THE WINDS AS THE AREA IS IN MILD NORTHWESTERLY FLOW IN THE WAKE OF THE PASSING SYSTEM. WITH PASSAGE OF COLD FRONT...THURSDAY WILL BE QUITE A BIT COOLER WITH A MORNING LOW IN THE MID 30S AND LOW 30S NEAR THE CANADIAN BORDER. THIS COULD BE THE LAST CHANCE THIS YEAR FOR FROST IN THE AREA..GIVEN THE LONG-TERM FORECAST. MARTIN .LONG TERM...THURSDAY NIGHT THROUGH TUESDAY... THE EXTENDED PERIOD STARTS WITH NEARLY ZONAL FLOW ACROSS THE NORTHERN ROCKIES. THE LATEST 12Z GFS RUN KEEPS THE ZONAL FLOW OVER MONTANA THROUGH THE WEEKEND. IT ALSO SHOWS AN AREA OF TROFFINESS PASSING THROUGH THE CENTRAL ROCKIES SOUTH OF THE ZONAL FLOW OVER MONTANA. GFS IS GENERATING SOME QPF ACROSS SOUTHERN AND CENTRAL MONTANA SATURDAY NIGHT AND SUNDAY DUE TO THIS TROFFINESS. THE 12Z RUN OF THE ECMWF IS ALSO MAINTAINING ZONAL FLOW OVER THE WEEKEND ACROSS MONTANA. IT ALSO HAS THE SAME AREA OF TROFFINESS ACROSS THE CENTRAL ROCKIES MOVING TO THE EAST SATURDAY NIGHT AND SUNDAY SOUTH OF THE REGION. THE ECMWF IS ALSO GENERATING QPF BUT HAS MORE OF A BULLSEYE ACROSS THE DAKOTAS. PRECIPITATION WILL BE POSSIBLE SATURDAY NIGHT AND SUNDAY SO WILL KEEP A SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS IN THE FORECAST FOR SATURDAY NIGHT THROUGH SUNDAY. AS THIS AREA OF TROFFINESS MOVES OFF TO THE EAST AN UPPER RIDGE BEGINS TO BUILD OVER THE WEST COAST. THE ZONAL FLOW OVER MONTANA WILL CHANGE TO NORTHWEST FLOW AND ALLOW A FAST MOVING SHORT WAVE TO MOVE OUT OF ALBERTA AND THROUGH EASTERN MONTANA ON MONDAY. SO WILL CONTINUE THE CHANCE OF SHOWERS AND THUNDERSTORMS IN THE FORECAST FOR MONDAY. ON TUESDAY THE UPPER RIDGE OVER THE WEST COAST WILL MOVE EASTWARD AND BUILDS INTO NORTHERN ALBERTA. THE RESULT WILL BE DRY CONDITIONS WITH WARMER TEMPERATURES FOR THE REMAINDER OF THE EXTENDED. RAS PREVIOUS DISCUSSION...FLAT UPPER RIDGE IN NEARLY ZONAL FLOW ALOFT WILL BRING DRY WEATHER TO THE AREA ON FRIDAY. FOR SATURDAY AND BEYOND...THE ZONAL FLOW ALOFT WILL GRADUALLY BECOME WNW EARLY NEXT WEEK. SOME WEAK WAVES PASSING THOUGH MONTANA MAY BE ENOUGH TO BRING A SHOWER OR THUNDERSTORM TO THE FORECAST AREA. NO SIGNIFICANT WEATHER SYSTEMS ARE EXPECTED AT THIS TIME. WILL MENTION A SLIGHT CHANCE OF SHOWERS OR THUNDERSTORMS FOR THE WAVES. FORRESTER && .AVIATION... WINDS WILL BRIEFLY DIMINISH THIS EVENING AS A LOW PRESSURE SYSTEM APPROACHES THE AREA. LOOK FOR SCATTERED MID AND HIGH CLOUDS MOST OF TONIGHT. A MIX OF LOW AND MID LEVEL CLOUDS WITH SCATTERED SHOWERS AND THUNDERSTORMS WILL ACCOMPANY A FRONTAL PASSAGE. MAY SEE BRIEF PERIODS OF MVFR CONDITIONS TONIGHT IN A SHOWER OR THUNDERSTORM. BEHIND THE FRONT STRONG NORTHWEST WINDS WILL INCREASE TO 20 TO 25KTS GUSTING TO 35KTS INTO WEDNESDAY. OTHERWISE...EXPECT VFR CONDITIONS. RAS/GAH && .GLASGOW WATCHES/WARNINGS/ADVISORIES... LAKE WIND ADVISORY FROM 9 AM TO 8 PM MDT WEDNESDAY FOR FORT PECK LAKE. && WEATHER.GOV/GLASGOW
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE GLASGOW MT 247 PM MDT TUE MAY 19 2009 MTZ016-017-022-023-200900- CENTRAL AND SOUTHEAST PHILLIPS-CENTRAL AND SOUTHERN VALLEY- GARFIELD-MCCONE- 247 PM MDT TUE MAY 19 2009 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTHEAST MONTANA. .DAY ONE...THIS AFTERNOON AND TONIGHT WINDS AROUND 20 MPH GUSTING TO 25 MPH WILL GRADUALLY DECLINE THIS EVENING. LAKE WIND ADVISORY WILL EXPIRE AT 6PM THIS EVENING FOR FORT PECK LAKE. THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON AND TONIGHT. ANY STORMS WHICH DEVELOP BEFORE SUNSET MAY BRIEFLY REACH SEVERE LIMITS. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY WIND WILL AGAIN PICK UP WEDNESDAY MORNING TO AROUND 25 MPH WITH HIGHER GUSTS. WINDS SHOULD DIMINISH IN THE EVENING. A LAKE WIND ADVISORY IS IN EFFECT FOR FORT PECK LAKE FROM 9 AM TO 8 PM ON WEDNESDAY. .SPOTTER INFORMATION STATEMENT... WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES. MTZ020-021-024>027-060-062-200900- WESTERN ROOSEVELT-PETROLEUM-RICHLAND-DAWSON-PRAIRIE-WIBAUX- SOUTHWEST PHILLIPS-EASTERN ROOSEVELT- 247 PM MDT TUE MAY 19 2009 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTHEAST MONTANA. .DAY ONE...THIS AFTERNOON AND TONIGHT THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON AND TONIGHT. ANY STORMS WHICH DEVELOP BEFORE SUNSET MAY BRIEFLY REACH SEVERE LIMITS. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .SPOTTER INFORMATION STATEMENT... WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.
The Glasgow radar (KGGW), 46 km away, was scanning. The volume nearest the first event began at 03:02 UTC.
3 hail. Local standard time, as filed.
A traveler reported quarter-size hail on Highway 2 from one mile west to four miles west of Frazer.
The public reported 1.25 hail near Frazer.
The public reported golf ball size hail near Frazer.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2009Every state in 2009This day in weather historyWarnings in Montana, May 2009
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: 159836, 159837, 159838.