Lack of February Precipitation Decreases Snowpack Percentages Across Montana Basins

Despite another round of promising weather outlooks, February did not bring the anticipated storms and was, overall, disappointingly dry. The main culprit was a stubborn ridge of high pressure off the West Coast that blocked Pacific moisture from flowing to the Rocky Mountain region. Southwest Montana only received 50-80% of its typical precipitation and even set record low accumulations for February, according to USDA Natural Resources Conservation Service (NRCS) SNOTEL period of record data. “January precipitation was below normal for most of Montana, and February was worse in many river basins,” said NRCS Hydrologist Eric Larson. Northwest Montana near the Continental Divide was one exception, receiving more than five inches of precipitation during the last several days of February.

Due to the overall lack of February precipitation, most snowpack percentages decreased from February 1. Exceptions were the Sun-Teton-Marias, Powder, and Tongue River basins which increased slightly. Montana’s current snowpack percent of normal ranges from 77% to 107%, with the Smith-Judith-Musselshell at the lower end of that range and the Kootenai and St. Marys at the upper end. “Last year much of the seasonal snowpack was recovered during February and we all hoped for the same this year. Unfortunately, the snowpack was overall in better shape on March 1 last year than it is now,” said Larson.

Basins currently lacking snow will need well above normal precipitation over the next couple of months to meet their typical snowpack peaks. “While the chances of meeting those peaks becomes less likely as the season progresses, it is not impossible to recover from a well below normal March 1 snowpack and it has happened before,” said Larson. In general, March and April are large contributors to water year precipitation, particularly east of the Continental Divide. The National Oceanic and Atmospheric Administration’s Climate Prediction Center does give hope for potential improvement to conditions over the next few weeks. The 6-10 day outlook also shows promise, with good chances for below average temperatures and above average precipitation across Montana.

March 1 streamflow forecasts generally follow the snowpack pattern across the state indicating below normal streamflows for April through July in southwest Montana and near to above normal west of the Continental Divide and in the streams along the Rocky Mountain Front. “The next couple of months will determine if basins with below normal snowpacks can add to their mountain reservoirs, reach normal peaks, and improve the outlook for streamflow this spring and summer,” said Larson. Additionally, springtime weather will be a major factor in streamflow. If spring weather warms up quickly, streams could peak early and have less water to deliver through the summer. Conversely, if it stays cool – and if more snow arrives next week as predicted – the water supply picture could be better.

A full report of conditions on March, 1 can be found in the monthly Water Supply Outlook Report available on the Montana Snow Survey website. In addition, real-time snow survey data can be found at http://www.mt.nrcs.usda.gov under Snow Survey.