The combination of snowmelt and heavy rainfall produced significant flooding over Blaine county, especially along the Milk River. State of emergency was declared for Blaine county of 05/23/11.
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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 TFX wrote it up.
The combination of snowmelt and heavy rainfall produced significant flooding over Blaine county, especially along the Milk River. State of emergency was declared for Blaine county of 05/23/11.
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 Great Falls, MT wrote its last area forecast discussion before the first event at May 21, 2:14 PM MST, 1 hour 11 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 314 PM MDT SAT MAY 21 2011 .DISCUSSION... UPPER LEVEL LOW CENTER LOCATED OVER SE MT AND WESTERN DAKOTAS MOST OF TODAY WILL MOVE DRIFT EAST OVERNIGHT. PLUME OF DEEP MOISTURE CIRCULATING AROUND THE BACK SIDE OF THE LOW WILL KEEP WIDESPREAD LIGHT RAIN OVER MUCH OF NORTH CENTRAL MT THIS EVENING WITH SCATTERED SHOWERS ELSEWHERE. A FEW ISOLATED THUNDERSTORMS WILL BE POSSIBLE THROUGH THIS EVENING NEAR THE WESTERN MTNS WHERE SOME BREAKS OF SUNSHINE THIS AFTERNOON HAVE CAUSED THE AIRMASS TO BECOME MORE UNSTABLE. LIGHT RAIN WILL PERSIST AFTER MIDNIGHT OVER EASTERN PORTIONS OF NORTH CENTRAL MT WITH PRECIPITATION DIMINISHING OVER WESTERN PORTIONS AS THE LOW DRIFTS EAST. AREA REMAINS UNDER A RELATIVELY WEAK FLOW ALOFT IN THE WAKE OF THE EXITING UPPER LEVEL LOW ON SUNDAY AND MONDAY AND WITH PLENTIFUL LOW LEVEL MOISTURE AND AFTERNOON INSTABILITY EXPECT SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS EACH DAY. PLEASE SEE HYDRO SECTION FOR ADDITIONAL INFORMATION. MONDAY NIGHT THROUGH SATURDAY...A LARGE UPPER LEVEL LOW PRESSURE AREA WILL REMAIN OFF THE PACIFIC NORTHWEST COAST THROUGH THE EXTENDED PERIOD. TWO SEPARATE WEATHER SYSTEMS WILL EJECT FROM THE MAIN UPPER LOW AND BRING AT LEAST A CHANCE OF SHOWERS WITH AFTERNOON/EVENING THUNDERSTORMS TO THE TFX CWA. THE FIRST SYSTEM WILL BRING THE BETTER CHANCE FOR SHOWERS OF THE TWO SYSTEMS...WHICH WILL AFFECT THE AREA MONDAY NIGHT THROUGH TUESDAY NIGHT. THE SECOND SYSTEM WILL FOLLOW CLOSE BEHIND THIS FIRST ONE...RESULTING IN A CHANCE OF SHOWERS AND AFTERNOON/EVENING THUNDERSTORMS CONTINUING THROUGH THURSDAY NIGHT. AN UPPER LEVEL RIDGE OF HIGH PRESSURE WILL DECREASE THE CHANCE FOR SHOWERS/THUNDERSTORMS SIGNIFICANTLY FOR FRIDAY AND FRIDAY NIGHT. HOWEVER...THE MAIN UPPER LEVEL LOW WILL SLOWLY APPROACH THE PACIFIC NORTHWEST COAST ON SATURDAY...FOR ANOTHER CHANCE FOR SHOWERS AND AFTERNOON/EVENING THUNDERSTORMS. WEAK COLD FRONTS WILL ACCOMPANY THE FIRST TWO SYSTEMS MENTIONED ABOVE...WHICH WILL ONLY BRIEFLY COOL SLIGHTLY ABOVE NORMAL TEMPERATURES TO SLIGHTLY BELOW NORMAL. COULSTON && .AVIATION... UPDATED 1800Z. EXPECT WIDESPREAD RAIN TO CONTINUE OVER CENTRAL MONTANA AND IN PARTICULAR AT KLWT. EXPECT GENERALLY IFR CEILINGS WITH OCCASIONAL MVFR VISIBILITIES. OF COURSE THERE WILL ALSO BE MOUNTAIN OBSCUREMENT. AT KHVR EXPECT GENERALLY MVFR CONDITIONS WITH OCCASIONAL VFR CONDITIONS. THERE ARE HINTS THAT RAIN MIGHT TAPER OFF LATER TONIGHT THEN INCREASE AGAIN SUNDAY MORNING. ELSEWHERE EXPECT VFR CONDITIONS. THERE WILL BE OCCASIONAL SHOWERS THIS AFTERNOON WITH MVFR CONDITIONS EXPECTED IN THOSE SHOWERS. HAVE BACKED OFF ON THE THREAT OF FOG FROM THE PREVIOUS FORECAST. OVER THE PLAINS THINK THERE WILL BE ENOUGH WIND TO PREVENT ITS FORMATION. OVER SOUTHWEST MONTANA THERE MIGHT NOT BE ENOUGH MOISTURE FOR FOG AT KBZN AND KHLN. && .HYDROLOGY... FLOOD WARNINGS CONTINUE FOR FERGUS...JUDITH BASIN...CHOUTEAU AND CASCADE COUNTIES WHERE NUMEROUS REPORTS HAVE BEEN RECEIVED OF ROADWAYS BEING AFFECTED BY HIGH WATER. IN ADDITION...A FLOOD WARNING WILL BE ISSUED FOR SOUTHERN BLAINE COUNTY WHERE REPORTS OF FLOODING ALONG PEOPLES CREEK NEAR HAYS AND LODGEPOLE HAVE BEEN RECEIVED. WHILE PRECIPITATION WILL GRADUALLY DIMINISH IN THESE AREAS LATER TONIGHT THROUGH TOMORROW...RUNOFF FROM MELTING SNOWPACK WILL LIKELY CONTINUE TO KEEP AREA STREAMS AT ELEVATED LEVELS WITH ADDITIONAL RISES STILL POSSIBLE THROUGH TOMORROW. A FLOOD WATCH HAS BEEN ISSUED FOR THE GALLATIN RIVER NEAR LOGAN. IN ADDITION...THE INFLUX OF WATER FROM SMALLER TRIBUTARIES WILL EVENTUALLY WORK INTO THE LARGER RIVERS OVER THE NEXT DAY OR SO. PARTICULARLY THE MISSOURI AT LANDUSKY LOOKS TO APPROACH FLOOD STAGE IN THE NEXT 24HRS WITH OTHER LARGER STEM RIVER LOCATIONS ALSO BEING CLOSELY MONITORED FOR ADDITIONAL HYDROLOGIC STATEMENTS. && .PRELIMINARY POINT TEMPS/POPS... GTF 47 65 47 66 / 60 60 50 60 CTB 46 65 44 67 / 20 60 60 50 HLN 48 68 48 68 / 20 50 40 60 BZN 41 68 43 67 / 30 40 50 60 WEY 35 56 36 58 / 40 40 50 60 DLN 41 65 41 64 / 20 40 50 60 HVR 50 66 48 69 / 100 70 40 40 LWT 45 62 43 63 / 100 80 40 60 && .TFX WATCHES/WARNINGS/ADVISORIES... FLOOD WATCH THROUGH SUNDAY MORNING GALLATIN...HILL... MEAGHER. FLOOD WARNINGS THROUGH MONDAY MORNING FOR CASCADE...FERGUS...JUDITH BASIN...CHOUTEAU COUNTIES AND BLAINE. FLOOD WATCH FOR THE GALLATIN RIVER NEAR LOGAN UNTIL FURTHER NOTICE. && WEATHER.GOV/GREATFALLS
HAZARDOUS WEATHER OUTLOOK...UPDATED NATIONAL WEATHER SERVICE GREAT FALLS MT 415 PM MDT SAT MAY 21 2011 MTZ011>013-047-050-051-054-055-221200- HILL-CASCADE-CHOUTEAU-BLAINE-JUDITH BASIN-FERGUS-MEAGHER-GALLATIN- 415 PM MDT SAT MAY 21 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL MONTANA...NORTH CENTRAL MONTANA AND SOUTHWEST MONTANA. .DAY ONE...TODAY AND TONIGHT A FLOOD WARNING IS IN EFFECT FOR JUDITH BASIN...BLAINE...CASCADE...CHOUTEAU AND FERGUS COUNTIES. A FLOOD WATCH IS IN EFFECT FOR HILL COUNTY IN NORTH CENTRAL MONTANA...AND FOR GALLATIN AND MEAGHER COUNTIES IN SOUTHWEST MONTANA. A FLOOD WATCH FOR THE GALLATIN RIVER NEAR LOGAN IS IN EFFECT. .DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY THE FLOOD WARNING IS IN EFFECT UNTIL MID AFTERNOON MONDAY. THE FLOOD WATCH IS IN EFFECT THROUGH AT LEAST SUNDAY MORNING. THE FLOOD WATCH FOR THE GALLATIN RIVER NEAR LOGAN WILL CONTINUE IN EFFECT UNTIL FURTHER NOTICE. ANOTHER WET STORM SYSTEM IS EXPECTED TO MOVE INTO THE REGION SUNDAY NIGHT AND COULD CONTINUE THROUGH TUESDAY. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS REQUESTED ALONG ALL CREEKS AND RIVERS IN THE ABOVE MENTIONED COUNTIES. ANY REPORTS OF FLOODING WOULD BE GREATLY APPRECIATED. MTZ008>010-014-015-044>046-048-049-052-053-221200- BEAVERHEAD-NORTHERN ROCKY MOUNTAIN FRONT-EASTERN GLACIER- CENTRAL AND SOUTHERN LEWIS AND CLARK-MADISON-TOOLE-LIBERTY- EASTERN PONDERA-SOUTHERN ROCKY MOUNTAIN FRONT-EASTERN TETON- JEFFERSON-BROADWATER- 415 PM MDT SAT MAY 21 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH CENTRAL MONTANA AND SOUTHWEST MONTANA. .DAY ONE...TODAY AND TONIGHT PERIODS OF RAIN AND HIGH MOUNTAIN SNOW WILL SPREAD ACROSS THE REGION TODAY AND TONIGHT. THE PRECIPITATION COULD CAUSE ADDITIONAL RISES ON CREEKS...STREAMS...AND RIVERS. .DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY PERIODS OF RAIN WILL CONTINUE THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK...AS ANOTHER WET STORM SYSTEM IS EXPECTED TO MOVE INTO THE REGION. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
416 PM MDT SAT MAY 21 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0900 PM FLOOD 11 S GRASS RANGE 46.87N 108.80W
05/20/2011 FERGUS MT DEPT OF HIGHWAYS
A PRIVATE DAM BROKE...ALLOWING WATER TO FLOW OVER
HIGHWAY 191. HIGHWAY REMAINED OPENED...WITH CONTROLLED
ACCESS THROUGH FLOODED AREAS.
&&
BRUSDAThe national radar mosaic for the moment the first event began.
1 flood. Local standard time, as filed.
Flooding occurred in the Hays and Lodgepole areas on Little Peoples, Hays and Lodge Pole creeks. State highway 66, route 11 and 15 were closed with flooding affecting six houses and post office. Fort Beltknap Indian Reservation also had significant flooding.
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, May 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: 370419.