Stay cautious, stay safe on rivers

ENNIS - According to the National Weather Service (NWS), we aren’t completely safe from flood threats yet, but hopefully we don’t have too much longer to wait before local rivers start to recede.

While the Madison River remains high, it currently faces little risk of flooding.

The rivers that need special attention and care are the Jefferson, the Yellowstone and the Missouri.

At the end of last week, the Jefferson’s stage was 8.47 feet, measured at the NWS gauge near Three Forks. The cutoff for minor flooding is eight feet, and for moderate flooding is 8.5 feet. Major flooding becomes a concern when the flood gauge reaches nine feet, and over the weekend the Jefferson topped out around 8.6, well within moderate flood range. With flood stages as low as 7.3 feet, water began to overflow the Jefferson’s banks near Silver Star and Waterloo, and by 7.5 feet some agricultural areas had begun to flood. Adding another 1.5 feet of water poses a serious threat.

The highest stage the Jefferson has ever seen in Three Forks was 9.88 feet in January of 1997. The river has topped the 9-foot stage five times since 1980, but early June could potentially see the sixth.

NWS issued a flood watch on Thursday, May 31, that stayed in effect until Friday morning, urging residents of the Cascade, Fergus, Judith Basin, Broadwater and Jefferson areas to be prepared to act should flooding become severe. With rain in the forecast, smaller tributaries can rise particularly quickly, and burn scars from summer fires can fall victim to flash floods. 

Other areas of the Jefferson could also see some high water, but none as severe as the Three Forks area. Near Twin Bridges, stage is forecast to reach 9.8 feet at an area where minor flood stage occurs at 10 feet.

By the end of the week, the Missouri River near Toston was flowing at 10.69 feet. At that gauge the moderate flood stage is 11 feet, and flow was expected to rise as high as 11.3 feet over the weekend. It did crest at over 11 feet but had subsided back to around 10.6 feet by Monday morning. Agricultural floods have been occurring around that area recently as well, including some areas near Highway 287.

The Yellowstone River, particularly near Livingston, has been flirting with its moderate flood stage of 10 feet on and off for several weeks. 

During the weekend it was forecast to continue rising, likely to become the third or fourth highest stage the river has seen. By Friday afternoon, June 1, the Yellowstone was flowing at 9.85 feet, causing some lowland overflows. The 10-foot mark could mean the flooding of homes and some streets, as well as parts of roads that lead to Yellowstone National Park.

A NWS warning was also issued for Park and Sweet Grass counties and was much more certain and is in effect until further notice, with flooding expected to impact both people and property in those areas. Flooding began earlier this year with faster-than-normal mountain snowmelt coupled with heavy rainfall. 

According to Kirk Miller of the U.S. Geological Survey, it’s difficult to tell when we’ll see the peak for flood risk, and it’s possible we haven’t yet. 

Miller oversees stream units across Montana and Wyoming that observe streamflows and run data comparing them to similar timeframes for other years. Both the Jefferson and Yellowstone rivers were flowing around the 97th percentile over the weekend, which means, Miller says, that if you took a hundred measurements of a river for a given day—say, a hundred June firsts—that the current streamflow falls higher than 97 of those.

“While recent rainfalls have contributed to the high flows we’ve seen, it’s also in combination with snowmelt runoff,” Miller says. “Since we still have snowpack left to melt, it depends on how warm it gets, how quickly it gets warm and how long it stays warm to determine whether we’ll see a higher peak later this season.”

The end of last week saw volatile weather across southwestern Montana, including severe hail in places and as much as an inch of rain over a 24-hour period, which increased the risk of rapidly changing conditions. Weather is expected to mellow over the first two weeks of June, which will provide a chance for the rivers to slow and flood risk to decrease. 

By the middle of June, the NWS estimates, the probability of minor to moderate flooding falls from upwards of 90 percent for the Jefferson and Missouri rivers to closer to 10 – 15 percent.

NWS reminds those recreating near rivers to use extreme caution. Never drive across flooded roads and watch for changing conditions. Most flood deaths occur in vehicles, and flash floods effect roads and other areas with poor drainage most significantly.