Dam operator reported a the failure of Lybeck Reservoir and BR-12 Reservoir.
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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.
Dam operator reported a the failure of Lybeck Reservoir and BR-12 Reservoir.
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 Apr 22, 8:59 AM MST, 2 hours 7 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 959 AM MDT FRI APR 22 2011 .UPDATE... BANDS OF MODERATE TO HEAVY SNOW CONTINUE TO MOVE SOUTH THROUGH CENTRAL MONTANA WITH ADDITIONAL SNOW ACCUMULATIONS OF 1 TO 3 INCHES POSSIBLE FROM NORTHERN LEWIS AND CLARK COUNTY EAST THROUGH CASCADE...JUDITH BASIN AND FERGUS COUNTIES. VISIBILITIES WILL LOWER TO LESS THAN ONE QUARTER OF A MILE WITH HAZARDOUS ROAD CONDITIONS. ONCE THIS AREA OF SNOW EXITS BY MIDDAY...DRIER CONDITIONS WILL FOLLOW AND ANY PEAKS OF SUNSHINE WILL HELP RAISE TEMPS TO AROUND 40 AND LOWER 40S THIS AFTERNOON. REMAINDER OF THE FORECAST IS ON TRACK. MLS && .AVIATION... UPDATED 1120Z. WIDESPREAD SNOW WITH IFR/LIFR CONDITIONS AND MOUNTAIN OBSCURATION WILL SLOWLY DECREASE DURING THE MORNING HOURS TO AREAS OF MVFR/IFR CONDITIONS THIS AFTERNOON. VFR CONDITIONS WILL PREVAIL ACROSS SOUTHWEST MONTANA TODAY WITH AREAS OF MVFR IN SNOW SHOWERS THIS AFTERNOON. AFTER 00Z SATURDAY...VFR CONDITIONS WILL PREVAIL WITH SOME MVFR/IFR CONDITIONS IN AREAS OF FOG AFTER 09Z. WILLIAMSON DC && .PREV DISCUSSION... /ISSUED 520 AM MDT FRI APR 22 2011/ TODAY THROUGH SUNDAY...AN UPPER LEVEL TROUGH AND ASSOCIATED SURFACE LOW PRESSURE SYSTEM WILL CONTINUE TO AFFECT PORTIONS OF THE FORECAST AREA TODAY. BULK OF PRECIPITATION HAS MOVED OUT OF SOUTHWEST MONTANA FOR NOW...WITH ANOTHER WAVE EXPECTED TO BRING SCATTERED TO NUMEROUS SHOWERS TO THE SOUTHWEST BY AFTERNOON. FEEL CONFIDENT THAT WIDESPREAD ACCUMULATING SNOWS HAVE ENDED IN THIS REGION SO HAVE DROPPED WINTER WEATHER HIGHLIGHTS IN THE SOUTH. BULK OF PRECIPITATION IS NOW AFFECTING CENTRAL MONTANA WITH MODELS KEEPING WIDESPREAD PRECIPITATION IN THIS REGION FOR MUCH OF THE DAY. LOW LEVEL UPSLOPE FLOW AND PRECIPITATION HAVE MANAGED TO COOL THE AIRMASS WITH MODERATE TO HEAVY SNOW AND GUSTY WINDS CREATING TREACHEROUS CONDITIONS. EARLIER TONIGHT I EXPANDED THE WARNING TO ALL ELEVATIONS IN JUDITH BASIN COUNTY AND FOR ELEVATIONS ABOVE 3500 FEET IN CASCADE AND FERGUS COUNTIES. HAVE ALSO EXPANDED THE WINTER WEATHER ADVISORY TO ELEVATIONS BELOW 3500 FEET IN CASCADE AND FERGUS AND FOR ALL ELEVATIONS ACROSS A BROAD SWATH OF NORTH CENTRAL MONTANA. AT THIS TIME TEMPERATURES REMAIN RATHER WARM IN HILL AND BLAINE COUNTIES SO EXPECT A MIX OF RAIN AND SNOW IN THIS AREA. THE UPPER TROUGH WEAKENS RAPIDLY AND MOVES EAST OVERNIGHT WITH PRECIPITATION RAPIDLY DIMINISHING ACROSS THE FORECAST AREA FRIDAY NIGHT. FOR SATURDAY THROUGH SUNDAY A SHORTWAVE RIDGE IS EXPECTED TO MOVE ACROSS THE REGION FOR MOSTLY CLEAR TO PARTLY CLOUDY SKIES AND A WARM UP BACK TOWARD SEASONABLE TEMPERATURES. THE NEXT SHORTWAVE SYSTEM IS EXPECTED TO APPROACH WESTERN MONTANA LATE SUNDAY AFTERNOON WITH SCATTERED SHOWERS MOVING OVER THE CONTINENTAL DIVIDE AND ACROSS SOUTHWEST MONTANA LATE IN THE DAY. MPJ SUNDAY NIGHT THROUGH FRIDAY...MODELS CONTINUE TO SHOW A RATHER COOL AND UNSETTLED WEATHER PATTERN THROUGH THE PERIOD. HOWEVER...DOWN SLOPE WINDS ACROSS THE ROCKY MOUNTAIN FRONT AND SOME OF THE SOUTHWEST VALLEYS...WILL RESULT IN MOSTLY DRY CONDITIONS...ESPECIALLY ON MONDAY...WEDNESDAY AND THURSDAY. THERE WILL BE A BROAD LONG WAVE TROUGH OVER THE PACIFIC NORTHWEST AND MONTANA THROUGH THE PERIOD. TEMPERATURES WILL BE A LITTLE COOLER THAN SEASONAL AVERAGE BETWEEN MONDAY AND WEDNESDAY WITH COOLER TEMPERATURES THURSDAY AND FRIDAY. THE SOUTHWEST WILL SEE MORE PRECIPITATION DURING THE PERIOD WITH THE BEST CHANCE OF SHOWERS ACROSS NORTH CENTRAL MONTANA MONDAY NIGHT AND TUESDAY. WILLIAMSON DC && .PRELIMINARY POINT TEMPS/POPS... GTF 40 27 51 30 / 100 20 10 10 CTB 40 27 51 30 / 70 10 10 10 HLN 44 26 53 30 / 60 20 10 10 BZN 40 20 51 25 / 50 30 10 10 WEY 30 8 36 15 / 60 20 10 0 DLN 40 20 46 25 / 40 10 10 10 HVR 46 31 56 32 / 80 10 10 10 LWT 39 23 43 24 / 100 30 10 10 && .TFX WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY UNTIL 6 PM MDT THIS EVENING CHOUTEAU... EASTERN GLACIER...EASTERN PONDERA...EASTERN TETON...NORTHERN ROCKY MOUNTAIN FRONT...SOUTHERN ROCKY MOUNTAIN FRONT. WINTER STORM WARNING UNTIL 6 PM MDT THIS EVENING JUDITH BASIN... MEAGHER. WINTER WEATHER ADVISORY UNTIL 6 PM MDT THIS EVENING FOR ELEVATIONS BELOW 3500 FEET FOR CASCADE...FERGUS. WINTER STORM WARNING UNTIL 6 PM MDT THIS EVENING FOR ELEVATIONS ABOVE 3500 FEET FOR CASCADE...FERGUS. A SMALL STREAM FLOOD ADVISORY IS IN EFFECT FOR JUDITH BASIN AND FERGUS COUNTIES UNTIL FURTHER NOTICE. && WEATHER.GOV/GREATFALLS
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE GREAT FALLS MT 410 AM MDT FRI APR 22 2011 MTZ050-054-231200- JUDITH BASIN-MEAGHER- 410 AM MDT FRI APR 22 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL MONTANA AND SOUTHWEST MONTANA. .DAY ONE...TODAY AND TONIGHT A WINTER STORM WARNING REMAINS IN EFFECT THROUGH 6 PM MDT. WIDESPREAD SNOW WITH AREAS OF HEAVY SNOW WILL CONTINUE THROUGH THE MORNING BEFORE DIMINISHING DURING THE AFTERNOON. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS REQUIRED FOR THIS MORNING. REPORTS OF SNOWFALL...ICE ACCUMULATION OR SIGNIFICANT RESTRICTIONS TO VISIBILITY WOULD BE GREATLY APPRECIATED. MTZ012-051-231200- CASCADE-FERGUS- 410 AM MDT FRI APR 22 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL MONTANA. .DAY ONE...TODAY AND TONIGHT A WINTER STORM WARNING FOR ELEVATIONS ABOVE 3500 FEET AND A WINTER WEATHER ADVISORY FOR ELEVATIONS BELOW 3500 FEET REMAIN IN EFFECT THROUGH 6 PM MDT. WIDESPREAD SNOW WITH AREAS OF HEAVY SNOW WILL CONTINUE THROUGH THE MORNING BEFORE DIMINISHING DURING THE AFTERNOON. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS REQUIRED FOR THIS MORNING. REPORTS OF SNOWFALL...ICE ACCUMULATION OR SIGNIFICANT RESTRICTIONS TO VISIBILITY WOULD BE GREATLY APPRECIATED. MTZ009-010-013-046-048-049-231200- NORTHERN ROCKY MOUNTAIN FRONT-EASTERN GLACIER-CHOUTEAU- EASTERN PONDERA-SOUTHERN ROCKY MOUNTAIN FRONT-EASTERN TETON- 410 AM MDT FRI APR 22 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH CENTRAL MONTANA. .DAY ONE...TODAY AND TONIGHT A WINTER WEATHER ADVISORY REMAINS IN EFFECT THROUGH 6 PM MDT. WIDESPREAD SNOW WILL CONTINUE THROUGH THE MORNING BEFORE DIMINISHING DURING THE AFTERNOON. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS REQUIRED FOR THIS MORNING. REPORTS OF SNOWFALL...ICE ACCUMULATION OR SIGNIFICANT RESTRICTIONS TO VISIBILITY WOULD BE GREATLY APPRECIATED. MTZ008-011-014-015-044-045-047-052-053-055-231200- BEAVERHEAD-HILL-CENTRAL AND SOUTHERN LEWIS AND CLARK-MADISON- TOOLE-LIBERTY-BLAINE-JEFFERSON-BROADWATER-GALLATIN- 410 AM MDT FRI APR 22 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH CENTRAL MONTANA AND SOUTHWEST MONTANA. .DAY ONE...TODAY AND TONIGHT THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
847 AM MDT FRI APR 22 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0845 AM HEAVY SNOW SW BELT 47.39N 110.93W
04/22/2011 E12.0 INCH CASCADE MT TRAINED SPOTTER
LOCATION IS TIGER BUTTE ELEVATION 4300 FEET
&&
EMANUELPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
909 AM MDT FRI APR 22 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0908 AM HEAVY SNOW LEWISTOWN 47.06N 109.43W
04/22/2011 M8.0 INCH FERGUS MT FOREST SERVICE
&&
JNSPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
954 AM MDT FRI APR 22 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0951 AM HEAVY SNOW 11 SSE LEWISTOWN 46.92N 109.34W
04/22/2011 M23.6 INCH FERGUS MT CO-OP OBSERVER
OBSERVER REPORTS A LIQUID EQUIVALENT OF 1.16 INCHES.
&&
JNSPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1014 AM MDT FRI APR 22 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1009 AM HEAVY SNOW 4 E WINDHAM 47.08N 110.05W
04/22/2011 E12.0 INCH JUDITH BASIN MT TRAINED SPOTTER
SPOTTER REPORTS 1.55 INCHES OF LIQUID EQUIVALENT OF
RAIN AND SNOW SINCE 9 PM YESTERDAY. MANY SNOW DRIFTS
WITH GUSTY WINDS.
&&
JNSPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1117 AM MDT FRI APR 22 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1045 AM HEAVY SNOW SIMMS 47.49N 111.93W
04/22/2011 E6.0 INCH CASCADE MT TRAINED SPOTTER
12 HOUR STORM TOTAL
&&
EMANUELPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1127 AM MDT FRI APR 22 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1126 AM HEAVY SNOW 1 NE RAYNESFORD 47.28N 110.71W
04/22/2011 E6.0 INCH JUDITH BASIN MT TRAINED SPOTTER
&&
JNSThe Glasgow radar (KGGW), 185 km away, was scanning. The volume nearest the first event began at 18:05 UTC.
1 flash flood. Local standard time, as filed.
Dam operator reported the failure of Lybeck Reservoir and BR-12 Reservoir with flood waters affecting Fifteen Mile Creek.
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, April 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: 370129.