Cooler weather and more moisture has kept area rivers from jumping into flood stage, but spring runoff is really just starting and residents in southwest Montana should still anticipate flooding, according to a National Weather Service hydrologist.
“We’re just at the beginning of this event,” said Gina Loss, with the weather service in Great Falls.
Last week, forecasters were anticipating the Big Hole River at Melrose to hit flood stage by Thursday. However, with the cooler weather that didn’t happen. Still the Big Hole is slowly creeping up and will likely hit flood stage at some point during run off, Loss said.
The models the weather service forecasters were using to predict stream flows were gauging their predictions on normal temperatures. However, temperatures in Montana have been cooler than normal for several months and continue to stay that way, she said.
This cooler pattern is the result of a La Nina event over portions of the Pacific Ocean, which generally means cooler temperatures and more moisture for the northern Rocky Mountains.
The La Nina is waning and what that means for both temperatures and precipitation in June is still unknown. There are equal chances of warmer or cooler than normal temperatures and more and less than normal precipitation, Loss said.
If temperatures stay cool, look for rivers to slowly rise over a long period of time as the mountain snow pack slowly recedes, she said. If the weather warms up and the area receives some rain, look for rivers to rise rapidly.
Snowpack in the Jefferson River Basin is still more than 147 percent of average. In the Madison River Basin the snowpack is better than 141 percent of average. Some snotel sites in the area have close to three feet of water stored up.
The immediate forecast through the coming weekend is for chances of rain across southwest Montana with the higher elevations receiving more snow, she said.