On this page you learn what types of flooding are typical in Montana and how do you protect yourself, your family and your home. You will also find out more about significant Montana floods. Finally, you'll find links to NWS offices that provide forecast and safety information for Montana, as well as links to our partners who play a significant role in keeping you safe.
Precipitation for April and May was above normal for Montana, and locally quite heavy. Cool spring temperatures delayed the melt of heavy snow in the mountains. Rain during May, coupled with much warmer temperatures and snowmelt late in May, resulted in the highest stream flows west of the Continental Divide in over 40 years. The Bitterroot, Clark Fork, Flathead and Kootenai Valleys were hardest hit. The Flathead River at Columbia Falls crested at 19.5 feet May 23, with all other area streams reporting record or near record stages. Bottom lands were flooded, including about 1,500 acres of crops. About 40 families were evacuated from their homes. Some livestock had to be left due to the rapid rises, and an estimated 100 head were reported lost. Many secondary highways were covered and several bridges were washed out or severely damaged. A $45,000 rip-rap project just completed and intended to protect a bridge across the Flathead near Kalispell was washed out and the bridge damaged. Flathead Lake continued to rise through month’s end reaching to within 1 foot of the record height of 2896.4 feet. Several farms flooded along the shore when dikes gave way. Estimates placed losses west of the Divide near $3 million.
June 3-4 then brought heavy rain over the Missouri and Sun River basins. Streams, already bankfull from precipitation and snowmelt in April and May, flooded lowlands from Three Forks to Great Falls on the Missouri River from town of Sun River to Great Falls on the Sun. Great Falls experienced considerable flooding. June 7, the Missouri River reached the highest stage recorded in the previous 52 years.
Montana’s Acting Governor, Ernest T. Eaton, proclaimed western Montana a disaster area Friday, June 4, stating “Unprecedented flood conditions now exist in the drainage areas at the headwaters of the Columbia, Yellowstone and Missouri Rivers in Montana. These conditions have resulted in and are causing severe damage to private and public property as well as threatening the public health and safety” (The Daily Missoulian, June 5, 1948). The Yellowstone River rose rapidly at Livingston, reaching over 5 feet above normal and only 4 inches below the all-time high at that point.
June 16-17, northern Lewis and Clark, Teton, Pondera, and Glacier Counties received the heaviest rains recorded to date. Precipitation from this storm far exceeded previous records for an area of about 1,000 square miles. Higher monthly rainfall totals included Valier, 11.24 inches; Gibson Dam, 11.13 inches; Babb, 10.43 inches; Browning, 10.14 inches; Choteau, 8.61 inches; Fairfield, 7.48 inches; Cut Bank, 7.30 inches; and Augusta, Â 6.68 inches. The greatest 48-hour amount recorded was 9.10 inches at Dupuyer. Several sites reported 2-day totals of 7 inches of more. Devastating flooding resulted with peak stream flows far exceeding previous records at many points.
The USGS determined the peak discharge of the Marias River near Shelby to be 40,200 cfs on June 18; previous peak was 29,500 cfs in 1907. In the Shelby area and at many points to the southwest, there was no record of the river and streams ever having been as high.
Considerable damage occurred with basement and street flooding in and near the storm’s centers. Severe damage was inflicted to roads and bridges in Pondera and Teton Counties. An estimated 28,000 acres of crop land were flooded. Total losses were estimated at over $1 million in spite of sparse population and limited development near the river. No loss of life was reported.
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Beginning about noon on June 7, light to moderate rain began over the area. During the night and into the morning of June 8, rainfall intensity was heavy along both side of the Continental Divide; at Summit, the rainfall rate exceeded 0.46 inches per hour for one 8-hour period. Several rivers and streams experienced flows exceeding their maximum of record by significant amounts. The USGS estimated the recurrence interval of the intensity of runoff to be 200 years on the Marias, Teton and Sun River drainages. The Sun River near Augusta peaked at 55,000 cfs; the previous record was 32,300 cfs on June 21, 1916. The Marias River near Shelby peaked at 154,000 cfs, the previous peak was 40,200 cfs June 18, 1948. Flow on the Marias River was exacerbated by the failure of Swift Reservoir, which released approximately 30,000 acre-feet on June 8. Flow in the
Two Medicine River was also augmented that same day by the failure of Lower Two Medicine Dam which had a capacity of 16,600 acre-feet (the 200-year recurrence interval includes adjustment for these two reservoirs.) Failure of Swift Dam and Lower Two Medicine Dam were directly responsible for the loss of 32 lives. The entire family of Tom Hall, which included his wife and 6 children, was lost while he watched helplessly from his truck some distance away. Hall cared for a Weather Bureau rain gage near Swift Dam. Surface transportation was paralyzed, not only over the affected area, but downstream as the flood crests moved forward. Highway and railroad bridges and embankments suffered seriously. Farms and ranches along the river bottoms were extensively damaged. Property losses exceeded $62 million.
The situation was complicated upstream on the Missouri above Canyon Ferry Reservoir where the heaviest June rains in years kept all streams relatively high most of the month. Simultaneous contributions from the Ruby, Beaverhead, and Big Hole Rivers all swelled by the frequent substantial, but not particularly heavy, June rainfall resulted in flooding on the Jefferson River from Twin Bridges to Three Forks June 11-14 and June 21-25. The river exceeded flood levels by nearly a foot both times. Two men died during the flooding June 11-14 when they were thrown from a horse crossing a flooded slough on the Jefferson River below Whitehall. A few bridge approaches and embankments were damaged between Twin Bridges and Three Forks. Minor flooding also occurred on some tributaries from Lewistown westward to Great Falls, but damage was comparatively small.
Greater-than-normal precipitation during late April and early May occurred across south central and southeastern Montana as well as central and northeastern Wyoming. Two storms in particular helped set the stage for flooding: the first event, April 26-30, which left the soil saturated, and the second, May 2-8, which included a snowstorm that deposited 15 to 32 inches of heavy, wet snow over much of central and eastern Wyoming. Liquid precipitation reports for this storm were above to well above normal: Gillette, WY, 5.30 inches; Sheridan Airport, WY, 4.09 inches; Ashland Ranger Station, MT, 3.70 inches; Yellowtail Dam, MT, 6.96 inches. A warming trend with temperatures in the 80s and 90s followed, culminating on May 15. The melting snow caused mountain streams to flow at bankfull before the May 16-19 storm.
Intense rain and some snow fell on the previously saturated ground in southeastern Montana and northeastern Wyoming, May 16-19. At Lame Deer, MT, 7.60 inches fell in the 72-hour period from May 17-19, setting a record for May in that region. The monthly total for Lame Deer was 12.44 inches, 9.85 inches above normal. Sonnett reported a 72 hour total of 5.51 May 17-19, with the total for the month at 10.53 inches. Several other sites in south central and south east Montana reported monthly totals of 5 to 8 inches. Widespread flooding occurred in the drainages of the Yellowstone River and its tributaries as well as the Belle Fourche, Cheyenne and North Platte Rivers. The previous maximum flood of record was exceeded at 48 gaged sites, with some sites exceeding their previous records by four times or more. There were 24 sites that equaled or exceeding the 100 year return period (1 percent chance of flood).
In Montana, flooding occurred on the Yellowstone River and its major tributaries; the Bighorn River, Tongue River, and Powder River. High antecedent flows, generally saturated ground conditions, and stock water reservoirs, already at or near capacity from previous precipitation events, contributed to the record and near-record flooding. The precipitation at the higher elevations was snowfall, which delayed runoff of some of the mountain streams. These streams peaked several days later when warm temperatures melted the snow. Flooding would have been much more severe if all the precipitation had been rainfall.
The only reported death resulting from the May 1978 flood occurred on Pryor Creek near Pryor when the victim left a flood-stranded automobile and was evidently washed away by the current. Flood damage to residences, roads, bridges, cropland, and buildings was extensive with costs exceeding $33 million. Nineteen counties in Montana and Wyoming were declared major disaster areas by the Federal Government.
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For the Yellowstone River near Livingston (89 years of record), the flood of 2011 is the largest with a flow of 40,600 cfs.
The Montana flooding of 2011 was unique in its breadth, both spatially and temporally. The flooding for 2011 was primed with summer and autumn 2010 precipitation, which increased soil moisture content. Through a series of events, flooding eventually hit all corners of the state at some time during winter, spring or summer.
With both daytime high temperatures and overnight lows averaging below freezing for much of December and January, river ice and ice jamming became a problem, particularly in west and central Montana. A portion of the town of Twin Bridges was flooded more than once by an ice jam that at times was as much as 10 miles long.
The cold weather that resulted in the ice jam also brought in some significant snowstorms. Missoula, Great Falls and Billings all experienced above, to well above normal, snowfalls for the winter season while Glasgow set a new record for seasonal snowfall. With the persistent cold temperatures, snow continued to accumulate from one storm to the next, rather than experience periods of melting between storms.
By March, Montana had a significant snow cover over plains, particularly north central and northeast, with snow water equivalent ranging from 4 to over 16 inches in some locations. As the shift to spring brought warmer temperatures in April, this snow rapidly melted. Smaller creeks and streams were quickly overwhelmed and larger rivers, most notably the Milk River, soon followed suit.
In late May a record breaking rainstorm hit much of central, south central and southeast Montana. Rainfall was more than 200 percent above normal for May in the eastern half of the state with large pockets that were more than 400 percent of normal. Return periods for May precipitation for areas in south central and southeast Montana were calculated to be from 250 to more than 1,000 years. The Musselshell Basin was one of the hardest hit. The flows in the Musselshell River were rivaling those in the Missouri River. Large areas of the town of Roundup were inundated.
These storms, which brought rain to the plains, were bringing snow to the mountains late in the season. Cooler spring temperatures delayed snowmelt, and mountain snowpack, which typically starts coming out in April, persisted well into June, reaching near record levels. Once the melt did begin, the runoff worked its way into streams already filled from plains snowmelt and recent rainstorms. Areas in southwest Montana and along the Rocky Mountain Front were hardest hit with this runoff. The town of Sun River was inundated.
As fortune would have it, little precipitation fell over the state after early June; however, as a result of the runoff from the plains snowmelt and the May rains, reservoirs were already filled, and water releases for irrigation were not needed. As the June snowmelt started moving downstream and into reservoirs already filled to capacity, high releases from the reservoirs became necessary, which further aggravated flooding further downstream. These releases continued through July and into early August. The Fort Peck Reservoir spillway was used a record of 121 straight days, with releases reaching a record 65,000 cfs.
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