Flood — Sweet Grass, Montana

2011-05-20 to 2011-05-27 · near Melville, Sweet Grass, Montana

Event narrative

Significant flooding occurred on creeks and streams across Sweet Grass County resulting in widespread lowland flooding and numerous county roads flooded, closing roads and resulting in significant damage. Numerous bridges also washed out. Specifically, Upper Deer, Lower Deer, Bridger, Sweet Grass, Big Timber and Otter Creeks Flooded. Specific roads flooded include; Anderson, Lower Sweet Grass, Mendinhaul, and Windsor Loop. At the height of the flooding, water was overtopping Interstate 90 from Mile Post 376 to 377. Damage estimates based on FEMA reviews and Individual Assistance approvals.

Wider weather episode

A Pacific low moved into the four corners region on the 17th and migrated northeast into the Dakotas through the 22nd, bringing another round of heavy precipitation aided by a tap of Gulf of Mexico moisture. Another system passed to the south on the 23rd and 24th, continuing the precipitation across the area. A new all-time daily precipitation record for Billings was set on May 24th. These two systems brought a total of 4 to 7 inches of precipitation to the area through the 25th. From May 29th through May 31st, another Pacific storm system moved northeast through the Billings Forecast Area, producing a half inch to 2 inches of precipitation across the area. A few areas received close to 3 inches of precipitation. The culmination of precipitation events resulted in historic flooding across the Billings Forecast Area. The monthly precipitation for May resulted in the wettest May ever recorded in Billings.

Widespread, severe flooding occurred across the entire Billings Forecast Area. Many roads and bridges were damaged or washed out across the area, including closure of I-90 between Livingston and Springdale eastbound lanes. The Montana Department of Transportation alone estimated over $36 million in damage to state and federal highways across the state of Montana. Hundreds of homes and trailers and multiple businesses experienced flood damage. There was damage to flood control dams. On May 19th, Montana Governor Brian Schweitzer declared an emergency for the state. In addition, the Governor requested that the President declare a major disaster for the State of Montana on June 1st, as a result of substantial widespread flooding. Governor Schweitzer deployed the Montana National Guard in Roundup and Crow Agency to help with flood response efforts May 28th and 29th. Flood emergencies were declared by the Governor for all but three counties in the Billings Forecast area. Emergency declarations included the Crow Reservation in Big Horn County. There were two fatalities, an elderly woman in Boyd in Carbon County fell into a flooded ditch and was swept away, and a man from Huntley in Yellowstone County was killed on an excavator when flooding from Pryor Creek overtook him. Multiple Emergency Operation Centers and Incident Commands were set up across the area, including in Billings in Yellowstone County, and in Park County to coordinate flood relief and response efforts.

A persistant upslope northeast flow into the region resulted in another round of locally heavy rainfall again on May 29-30th. An additional 1-2 inches of rainfall were noted, especially for the Beartooth and Big Horn Mountain foothill areas. This resulted in prolonged or even renewed flooding in some locations through the end of the month.

View location on OpenStreetMap → (46.0376, -110.1792)

Source: NOAA Storm Events Database, event_id 308816. Narrative written by the NWS forecast office that issued the report.