Posted: Apr 5, 2013 1:41 PM by Meteorologist Mike Heard
Updated: Apr 5, 2013 1:42 PM
April 1 Low Elevation Snowpack Drags Down Statewide Average
BOZEMAN, Mont., April 5, 2013 -Entering the month of March most basins around the state of Montana were near to slightly below normal, with the St. Mary-Milk River Basin having the highest percentage of basin normal at 108 percent, and the Bitterroot River Basin with the lowest percentage at 85 percent, according to snow survey data from the USDA Natural Resources Conservation Service (NRCS).
Through the month, the weather patterns continued to favor the northern basins in the state while the central and southern parts of the state experienced long periods of high pressure, which led to above average temperatures and below average precipitation. Central and southern basins saw a 3 to 9 percent decrease in basin percentage of normal while the basins in northern Montana saw a 4 to 7 percent gain in basin percentage of normal.
As of April 1, the St. Mary-Milk River Basin continues to have the highest percentage of normal at 106 percent, and the Bitterroot River Basin continues to be the lowest at 84 percent. "Overall, the variability in the weather patterns across the state balanced out during the month of March changing the statewide percentage of normal only 1 percent below where it was just a month ago on March 1," said Brian Domonkos, NRCS water supply specialist. "That slight change brought the state to 92 percent of normal."
Snowpack typically reaches its maximum during the month of April so weather in April has a big impact on the timing and volume of stream flows through the spring and into the summer. According to NRCS, warm weather experienced during the end of the month of March has begun to melt low-elevation snowpacks in most parts of the state. "The mid and upper elevations are still holding on, but are slowly beginning to trend in this direction," Domonkos said. "Continued warm weather will most likely continue to change the snowpack at these elevations to isothermal, starting the larger scale runoff process."
The mid and upper elevations of the basins yield the bulk of the water supply across the state, so continued monitoring of the snowpack will be required to determine the timing and volume of this year's runoff.
Given the current snowpack in place and near normal future precipitation and temperatures, streamflows are predicted to be below average in most basins this season. The table below provides normalized streamflow forecasts for each basin.
Below are the averaged river basin streamflow forecasts for April 1 through July 31. These forecasts assume near normal moisture and runoff conditions April through July.