BILLINGS — A hefty mountain snowpack in the Northern Rockies has driven down the summer wildfire potential and bumped up prospects that farmers in most of Montana and Wyoming won’t go dry.
As for flooding, government forecasters say the coming weeks will make all the difference.
A relatively even warm-up would keep streams and rivers in check. Too much warm weather and flooding could threaten downstream communities.
Late season snows three years ago led to flooding in the Missouri River basin that swamped hundreds of homes in Montana and vast areas of mostly farmland in North and South Dakota, Nebraska, Iowa, Kansas and Missouri.
But 2011 stood out as an anomaly caused by a series of unusual late snowfalls and heavy rain events that continued into late May and early June, said Lucas Zukiewicz, a hydrologist with the U.S. Department of Agriculture’s Natural Resources Conservation Service in Bozeman.
He forecast above-average stream flows across most of the region through July 31.
“The timing and magnitude of how that works out in the rivers themselves is going to be weather-dependent,” Zukiewicz said. “It’s really important to remember each basin differs in when it peaks based on where it’s located.”
April snowfalls fell short of expectations after a record-breaking March. Yet because there hasn’t been a major shift in weather patterns, much of that snow remains locked at higher elevations.
The delay in the melt has lowered the danger of early season wildfires, according to the National Interagency Fire Center, which is predicting that 2014’s fire season could come on later than normal, particularly in northern Wyoming.
The lingering snowpack is keeping trees and other fuels at higher elevations wet, and that’s expected to remain the case in most areas until August, the Boise-based agency said in its most recent monthly outlook.
But the confidence in a less-active fire season begins to fade beyond mid-August, meaning there’s potential for blazes to become more severe as the summer wears on.
Also uncertain is whether the eventual melt-off will send water rushing down from the mountains in a sudden pulse or more gradually.
The highest streamflows in Montana will be in the Smith, Judith and Musselshell River basins, forecasters say. That includes towns such as Roundup, which was largely cut off from outside access by the 2011 floods and already saw some minor flooding caused by ice jams in March.
Only one area of the state — the extreme headwaters of the Jefferson River basin in southwest Montana — is forecast to have below-average streamflows.
For Wyoming, streamflow volumes during the upcoming snowmelt are expected to be well above average across the Powder, Tongue and Shoshone watersheds. The Little Wind and Sweetwater River basins in central Wyoming are among the few areas with below average volumes forecast.
“If we don’t get any more snow in the mountains we’re still going to get a good water supply,” said James Fahey with the National Weather Service in Riverton, Wyoming. “The snowpack is lower than 2011, but not much.”