Next three months determine drought, flood scenarios
Date posted: March 13, 2014
SHERIDAN — Precipitation in Wyoming was nearly 180 percent of average for the month of February, but the months of April, May and June will be the ones that determine whether the state is in for a summer drought.
The Powder River Basin, like others in the state, is expected to have above normal snowmelt streamflow volume this spring.
The Powder and Tongue river watersheds are 110 to 125 percent above normal. Wyoming Hydrologist for the National Oceanic and Atmospheric Administration Jim Fahey said Sheridan’s two closest rivers have some advantage over others in the state.
“With runoff, each section of Wyoming is different because morphology of streams,” Fahey said. “If you’re just looking at the Tongue in Sheridan, that one can handle pretty good runoff and has in the past five years.”
Fahey said the most hazardous situation that might cause flooding near Sheridan is when rain drainage piles on top of snowmelt as it comes off the mountain.
“The Tongue does pretty well and the portions of the Powder River do well on the eastern side,” he said.
When asked about the recent ice jams that caused flooding in more central communities around the state, Fahey said jammed ice is a common occurrence each spring, but that it’s not a problem that gets a lot of public attention until it happens near or within a heavily populated area. He added that ice jams are a finite phenomenon because as the ice melts and water finds another way through the constriction, the problem goes away.
Factors on a river itself that might predispose the waterway for an ice jam and subsequent flooding are sharp turns, man-made structures — bridges — in the water, and deep, wide, slow-moving sections of calmer water that provide for the formation of thick ice that eventually must break apart.
“Most channels now are starting to break through,” he said. “Water has a way of flowing through river channels instead of going through property.”
Fahey said that May will likely mark the spring rush of large volumes of water in the state’s basins.
He said it’s too soon to say whether Wyoming’s forest land is in the clear of an extra dangerous fire season.
“April, May and early June are so important east of the divide,” he said. “It makes or breaks us.”
Wyoming’s cumulative annual precipitation is roughly 135 percent above normal across the state, while mountain snowpack ranges between 120 and 135 percent of average. Reservoir storages are around 90 percent of average for early March.