Flooding in Montana, May 10 to 17, 2011

Name: Flooding in Montana, May 10 to 17, 2011
Start: 2011-05-10T01:05
End: 2011-05-17T12:00
Location: Montana

May 10 to 17, 2011 · NWS BYZ · 6 events in 6 counties and zones

Where it happened

Every event with a place to put it. Tap one for its entry below.

Tornadoes
Tropical storms and surge
Floods
Wind
Hail
Winter weather
Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
Other

Open the live radar over this ground

The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 6

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.

What happened

The episode as NWS BYZ wrote it up.

A significant spring storm impacted south central Montana May 8-11 as a moist and slow moving storm system impacted the region. Rain began to move into the region late Sunday, May 8th with the heaviest rainfall Monday into Tuesday. Some embedded thunderstorms enhanced rainfall across portions of the region late on Monday, the 9th. Widespread rainfall amounts of 2-4 inches occurred. The heavy rainfall also combined with some mid elevation snowmelt from nearby mountains to enhance flooding in some foothill locations. As a result, widespread lowland flooding was reported along with some damage to roads and structures.

What forecasters said that day

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 Billings, MT wrote its last area forecast discussion before the first event at May 9, 8:46 PM MST, 4 hours 19 minutes earlier.

Area forecast discussion, May 9, 8:46 PM MST, 4 hours 19 minutes before

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BILLINGS MT
946 PM MDT MON MAY 9 2011

.SHORT TERM...VALID FOR TUE AND WED...

UPDATE TO FORECAST AND WRKAFP. LINE OF THUNDERSTORMS WAS NEARLY
STATIONARY OVER CUSTER AND POWDER RIVER COUNTIES THIS EVENING DUE TO
SURFACE CONVERGENCE OVER THIS AREA. ANOTHER AREA OF RAIN WAS FROM
KBIL W ON RADAR. HEAVY RAIN HAS BEEN REPORTED THROUGHOUT THE EVENING
FROM KBIL E. IR SATELLITE IMAGERY SHOWED COLD CLOUD TOPS OVER THE
THUNDERSTORM AREA. LOW PRESSURE CENTERED OVER W NE WAS PUMPING
MOIST AIR INTO THE AREA ON DEEP EASTERLY FLOW UP TO 700 MB. LATEST
RUC AND NEW WRF HAD A SECONDARY 700 MB LOW MOVING NE THROUGH WY
OVERNIGHT BRINGING STRONG VERTICAL MOTION TO AREAS E OF KBIL.
UPPER DIFLUENCE OVER THE AREA THIS EVENING WILL GRADUALLY WEAKEN
OVERNIGHT AS THE UPPER LOW ELONGATES TO THE NE. WILL HAVE PLENTY
OF LIFT AND MOISTURE FROM THE SYSTEM TO KEEP HEAVY RAIN GOING
THROUGH THE NIGHT...AND NEW WRF CONTINUES THE PRECIPITATION INTO
TUE. HAVE ISSUED AN AREAL FLOOD WATCH FROM MUSSELSHELL S TO
SHERIDAN COUNTIES THROUGH 00Z WED.

HAVE ADDED THE MENTION OF THUNDER E OF KBIL AFTER 06Z TONIGHT DUE TO
STRONG SYSTEM DYNAMICS.

SNOTEL TEMPERATURES WERE GENERALLY AT OR ABOVE FREEZING THIS
EVENING. NEW WRF BRINGS 700 MB TEMPERATURES DOWN TO -4 DEGREES C BY
12Z TUE. NOT CONFIDENT IN THE HEAVY SNOW AMOUNTS OVER THE MOUNTAINS
DUE TO THE WARM AIRMASS BUT WILL LEAVE WARNINGS/ADVISORY ALONE FOR NOW.
ARTHUR

.LONG TERM...VALID FOR THU...FRI...SAT...SUN...MON...

LONG TERM FORECAST IS DOMINATED BY RIDGING OVER THE AREA WHICH
NORMALLY BODES WELL FOR WARM AND DRY CONDITIONS. HOWEVER THIS
RIDGE IS LOOKING MORE AND MORE WET WITH THE SYSTEM THATS CURRENTLY
IMPACTING THE REGION NOT MOVING DOWNSTREAM FAR ENOUGH TO STOP
IMPACTING THE EASTERN HALF OF THE FORECAST AREA AND A VERY LARGE
AND STRONG STORM SYSTEM ENCOMPASSING MOST OF THE WESTERN UNITED
STATES PUSHING ENERGY AND PACIFIC MOISTURE OVER THE AREA FROM THE
SOUTHWEST. TEMPERATURES STILL LOOK WARM...THOUGH CLOUD COVER WILL
PUT DOWNWARD PRESSURE ON TEMPERATURES. WITH WIDESPREAD
PRECIPITATION IN THE 2 TO 4 INCH RANGE EXPECTED OVER THE NEXT
COUPLE OF DAYS THERE WILL BE PLENTY OF LOW LEVEL MOISTURE AROUND
ONCE TEMPERATURES BEGIN TO CLIMB INTO THE 60S AND LOWER 70S
THURSDAY AND FRIDAY. THIS WOULD POINT TO ISOLATED TO SCATTERED
SHOWERS AND THUNDERSTORMS DEVELOPING DURING THE AFTERNOON AND
EVENING HOURS AND ADJUSTED GRIDS IN THIS DIRECTION. A BACKDOOR
FRONT COURTESY OF THE CURRENT SYSTEM REMAINING JUST TO THE
NORTHEAST OF THE FORECAST AREA AND RETROGRADING SOME LOW LEVEL
COLD AIR BACK INTO THE AREA WILL MOVE IN FRIDAY NIGHT. THE BOUNDARY
THIS COLD AIR CREATES WILL BE A FOCUS FOR CONVECTION SATURDAY AND
SUNDAY AS STRONGER DIFFLUENT SOUTHWESTERLY FLOW ALOFT PRESSES IN
FROM THE WESTERN SYSTEM. MAY NEED TO INCREASE POPS FOR THESE
WEEKEND EARLY NEXT WEEK PERIODS AS A RESULT.

WITH MUCH WARMER TEMPERATURES BY LATE IN THE WEEK...AND
TEMPERATURES IN THE HIGHER ELEVATIONS STAYING ABOVE FREEZING
EXPECT MOUNTAIN SNOW PACK TO BEGIN MELTING IN ERNEST. WITH
SIGNIFICANTLY ABOVE NORMAL SNOW PACK WILL LIKELY SEE SIGNIFICANT
RISES ON AREA WATERWAYS BY NEXT WEEKEND...IN ADDITION TO RISES
CAUSED BY THE EARLY WEEK RAIN/SNOW. PERSONS WITH INTERESTS NEAR
AREA STREAMS AND RIVERS SHOULD BE ALERT FOR RISING WATER LEVELS
THROUGH THE NEXT WEEK. CHAMBERS

&&

.AVIATION...

LARGE STORM SYSTEM WILL CONTINUE TO BRING MVFR TO IFR CONDITIONS
ACROSS MUCH OF THE AREA. THIS STORM WILL CONTINUE TO CAUSE
EXTENSIVE RAIN SHOWERS WITH ISOLATED THUNDERSTORMS UNTIL TUESDAY
AFTERNOON. BORSUM

&&

.PRELIMINARY POINT TEMP/POPS...

    TUE     WED     THU     FRI     SAT     SUN     MON
-----------------------------------------------------------
BIL 040/051 038/061 039/071 043/072 046/067 044/070 048/072
    99/R    51/B    12/T    22/T    22/T    22/T    23/T
LVM 038/052 032/061 034/070 040/073 044/068 041/067 041/068
    98/R    31/B    12/T    22/T    22/T    22/T    23/T
HDN 042/053 038/061 039/072 042/074 045/070 044/074 046/075
    99/W    61/B    12/T    22/T    22/T    22/T    22/T
MLS 043/048 039/059 039/068 039/068 042/062 043/065 046/070
    9+/W    62/R    12/T    21/U    11/U    11/B    12/T
4BQ 043/052 037/059 038/068 039/070 042/067 042/071 046/071
    99/W    62/R    12/T    21/U    11/U    11/B    12/T
BHK 045/050 038/057 037/064 037/065 039/060 041/064 045/067
    9+/W    63/R    12/T    21/U    11/B    22/W    12/T
SHR 040/047 035/055 035/066 039/070 042/069 042/072 046/072
    +9/W    72/R    12/T    22/T    22/T    22/T    22/T

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...FLOOD WATCH IN EFFECT THROUGH TUESDAY AFTERNOON FOR ZONES
      29>33-35>38-57-58.
     WINTER STORM WARNING IN EFFECT UNTIL 6 PM MDT TUESDAY FOR
      ZONES 67-68.
WY...FLOOD WATCH IN EFFECT THROUGH TUESDAY AFTERNOON FOR ZONE 99.
     WINTER WEATHER ADVISORY IN EFFECT UNTIL MIDNIGHT MDT TUESDAY
      NIGHT FOR ZONE 98.

&&

WEATHER.GOV/BILLINGS

Hazardous weather outlook, May 9, 9:03 PM MST, 4 hours 2 minutes before

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE BILLINGS MT
1003 PM MDT MON MAY 9 2011

MTZ028>042-056>058-063>068-WYZ098-099-110415-
SOUTHERN WHEATLAND-MUSSELSHELL-TREASURE-NORTHERN ROSEBUD-CUSTER-
FALLON-NORTHERN STILLWATER-YELLOWSTONE-POWDER RIVER-CARTER-
SOUTHERN BIG HORN-EASTERN CARBON-NORTHERN PARK-
NORTHERN SWEET GRASS-GOLDEN VALLEY-RED LODGE FOOTHILLS-
NORTHERN BIG HORN-SOUTHERN ROSEBUD-JUDITH GAP-PARADISE VALLEY-
LIVINGSTON AREA-BEARTOOTH FOOTHILLS-ABSAROKA/BEARTOOTH MOUNTAINS-
CRAZY MOUNTAINS-NORTHEAST BIG HORN MOUNTAINS-SHERIDAN FOOTHILLS-
1003 PM MDT MON MAY 9 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL
MONTANA...SOUTH CENTRAL MONTANA...SOUTHEAST MONTANA AND NORTH
CENTRAL WYOMING.

.DAY ONE...TONIGHT

RAIN...HEAVY AT TIMES...WILL OCCUR ACROSS THE AREA TONIGHT.
SCATTERED THUNDERSTORMS WILL ALSO OCCUR EAST OF BILLINGS. THE
RAIN FALLING ON ALREADY SATURATED GROUND WILL BRING THE THREAT OF
FLOODING TO MUSSELSHELL...YELLOWSTONE...BIG HORN AND SHERIDAN
COUNTIES EAST OVERNIGHT. HAIL WILL BE POSSIBLE WITH A FEW OF THE
THUNDERSTORMS OVERNIGHT.

OTHERWISE...HEAVY SNOW WILL OCCUR OVER THE BEARTOOTH/ABSAROKA AND
CRAZY MOUNTAINS TONIGHT.

PEOPLE LIVING NEAR OR PLANNING ACTIVITIES ON AREA WATERWAYS
SHOULD BE ALERT TO POSSIBLE FLOODING.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

THE STORM SYSTEM WILL CONTINUE TO IMPACT THE ENTIRE REGION ON
TUESDAY AND WILL BRING PERIODS OF SIGNIFICANT PRECIPITATION AND
POSSIBLE FLOODING. HEAVY SNOW WILL CONTINUE OVER AREA MOUNTAIN RANGES. A
MIX OF RAIN AND SNOW IS EXPECTED ALONG THE ADJACENT FOOTHILLS WITH
HEAVY RAINFALL OVER THE PLAINS.

PEOPLE LIVING NEAR OR PLANNING ACTIVITIES ON AREA WATERWAYS
SHOULD BE ALERT TO POSSIBLE FLOODING ON TUESDAY.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.

In the hours before

Special weather statement, May 9, 9:19 PM MST, 3 hours 46 minutes before

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BILLINGS MT
1019 PM MDT MON MAY 9 2011

MTZ037-100515-
CARTER MT-
1019 PM MDT MON MAY 9 2011

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHERN CARTER COUNTY UNTIL 1115
PM MDT...

AT 1012 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING
STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM 41 MILES EAST OF
ALZADA TO 9 MILES SOUTHEAST OF ALZADA...AND MOVING NORTHEAST AT 30
MPH.

HAIL UP TO ONE-HALF INCH IN DIAMETER IS EXPECTED WITH THESE STORMS...
ALONG WITH HEAVY RAIN.

AREAS AFFECTED BY THESE STORMS INCLUDE...RIDGEWAY...ALBION AND
CAPITOL.

IF THREATENING WEATHER APPROACHES YOUR AREA...TAKE SHELTER IN A
STURDY BUILDING.

IN ADDITION...THESE STORMS 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 4499 10462 4501 10504 4588 10406 4585 10402
      4500 10403
TIME...MOT...LOC 0418Z 224DEG 24KT 4480 10322 4490 10356
          4499 10421

Special weather statement, May 9, 10:25 PM MST, 2 hours 40 minutes before

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BILLINGS MT
1125 PM MDT MON MAY 9 2011

MTZ033-037-100630-
CARTER MT-FALLON MT-
1125 PM MDT MON MAY 9 2011

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN FALLON AND NORTHERN
CARTER COUNTIES UNTIL 1230 AM MDT...

AT 1124 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING
AN AREA OF STRONG THUNDERSTORMS OVER THE NORTHEAST HALF OF CARTER
COUNTY THAT WERE GENERALLY LOCATED NORTH AND NORTHWEST OF CAPITOL.
THESE STORMS WERE MOVING NORTH AT 40 MPH.

HAIL UP TO ONE-HALF INCH IN DIAMETER IS POSSIBLE WITH THESE STORMS...
ALONG WITH HEAVY RAIN AND FREQUENT DANGEROUS LIGHTNING.

AREAS AFFECTED BY THESE STORMS
INCLUDE...EKALAKA....RIDGEWAY...BELLTOWER...MILL IRON...MEDICINE
ROCKS ST PARK...WEBSTER AND WILLARD.

IF THREATENING WEATHER APPROACHES YOUR AREA...TAKE SHELTER IN A
STURDY BUILDING.

LAT...LON 4532 10425 4577 10498 4579 10494 4602 10494
      4610 10452 4621 10437 4615 10404 4538 10403
TIME...MOT...LOC 0524Z 159DEG 36KT 4551 10421

The radar

The national radar mosaic for the moment the first event began.

Open the radar archive at this moment

Event by event

6 flood. Local standard time, as filed.

Flood, Park

When: May 10, 1:05 AM MST to May 17, 12:00 PM MST
Where: Park County, 1.42 mi ESE of Hoopers to 1.53 mi ESE of Hoopers
Cause: Heavy Rain / Snow Melt
Reported by: County Official
Coordinates: 45.659, -110.655

Park County officials reported flooding on Billman and Trail Creeks southwest of Livingston due to heavy rainfall and mid elevation mountain snowmelt. Numerous roads flooded (Miller, Trailer Creek, Old Yellowstone, Cokedale, Rendezvous Trail) in the region with water overtopping them with lowland flooding in nearby farmland. Several homes and trailers flooding. Several farms were cutoff and unreachable because of flooded raodways. The Shields River in central Park County ran high and out of it's banks, flooding nearby farmland.

Flood, Rosebud

When: May 10, 7:00 AM MST to May 11, 7:00 AM MST
Where: Rosebud County, 58.2 mi E of Brandenberg to 59.86 mi WNW of Colstrip
Cause: Heavy Rain
Reported by: Emergency Manager
Coordinates: 45.817, -104.971

Widespread flooding resulting in road closures occurred across the northern half of Rosebud County. Flooding in low lying areas along Reservation Creek west of Forsyth was reported. Across northwest Rosebud County, flooding on Home Creek resulted in significant water over Bascom Road.

Flood, Custer

When: May 10, 7:00 AM MST to May 11, 7:00 AM MST
Where: Custer County, 33.15 mi SSE of Mizpah to 9.3 mi WSW of Moon Creek
Cause: Heavy Rain
Reported by: Emergency Manager
Coordinates: 45.817, -104.971

Widespread flooding resulted in road closures occurring across Custer County with numerous roads reported as washed out. Significant flooding was reported along the Powder River as well as its tributaries. Dry, Spring, Strevel and Mizpah Creeks all reported flooding. Major flooding occurred from north of Powderville to Mizpah. Water overtopped Pumpkin Bridge on Pumpkin Creek. A storm spotter 16 miles south of Miles City on Highway 59 indicated this was the worst flooding that they had seen in that area in 25 years. There was significant lowland flooding in the Yellowstone Valley area of Northeast Miles City where Emergency Travel Only was declared for a time. A water rescue was required when a paper carrier in the valley washed off the road.

Tongue River flooding on May 10-11th resulted in Custer County declaring a flood disaster and a water rescue due to Graveyard Creek washing out Kinsey Road. A levee system was damaged in Miles City. In addition, Custer County ran out of road closed signs due to extent of washed out roads.

Flood, Big Horn

When: May 10, 10:30 AM MST to May 12, 8:00 AM MST
Where: Big Horn County, 1.09 mi E of St Xavier to 20.78 mi SE of Yellowtail
Cause: Heavy Rain
Reported by: Emergency Manager
Coordinates: 45.473, -107.698

Numerous reports of small stream and lowland flooding were reported along streams and creeks across Big Horn County. Water was reported over highway 313 towards the Fort Smith area. As a result of the flooding, a few homes were evacuated.

Flood, Yellowstone

When: May 10, 10:30 AM MST to May 11, 7:00 AM MST
Where: Yellowstone County, 36.97 mi S of Bull Mtn to 4.82 mi SE of Lockwood
Cause: Heavy Rain
Reported by: Emergency Manager
Coordinates: 45.473, -107.698

Significant flooding occurred in the Briarwood Subdivision and golf course in South Billings along Blue Creek. Several homes, structures and barns were inundated with water with evacuations required in the area. Damage occurred to the golf course due to the flooding and several bridges washed out on the course.

Flood, Treasure

When: May 10, 10:30 AM MST to May 11, 7:00 AM MST
Where: Treasure County, 6.59 mi NNE of Sanders to 15.19 mi SSE of Sarpy Jct
Cause: Heavy Rain
Reported by: Emergency Manager
Coordinates: 46.370, -107.055

Several roads across Treasure County flooded, especially northeast of Hysham area.

What these are

Flood: Flooding that develops more slowly than a flash flood: rivers leaving their banks, or water standing over land for an extended time.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in Montana in 2011 Every state in 2011 This day in weather history Warnings in Montana, May 2011

Sources

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: 308097, 308102, 308104, 308099, 308100, 308109.