May 2016 Water Supply Status and Outlook

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The Beaverhead County Drought Task Force met on Monday May 9th. Donald Britton of the National Weather Service in Great Falls gave a presentation about how the water year is shaping up and what Beaverhead County can expect over the coming days and weeks. For the month of April, southern Beaverhead County came out a little drier than the monthly average, while the valleys in the northern part of the county were a little wetter. The mean temperatures for April were warmer than normal in southwest Montana, and much warmer than normal in northwest Montana.

Heading into the winter, we expected to see warmer and drier conditions due to the very strong El Nino conditions in the equatorial Pacific Ocean. The El Nino conditions peaked in mid November and have been diminishing since then. Looking back at our water year to date (October 2015 – April 2016), we can see that the El Nino did bring warmer mean winter temperatures to all of Montana, but temperatures in the valleys of Beaverhead County actually were the closest to normal in the whole state. Water year to date precipitation has been above normal thus far for the Red Rock, Beaverhead, and Big Hole valleys. This provides a good example of how even though El Nino may make certain conditions more likely (like warmer and drier winter weather in Montana), our seasonal forecasting science is still subject to uncertainty.

Clark Canyon Reservoir’s current storage is ahead of where it was at this time in 2014 and 2015, but it is still a little below average for this time of year. Meanwhile, Lima Reservoir’s storage is also currently ahead of where it was at this time in 2014 and 2015, but it is slightly above average for this time of year.

The NRCS Surface Water Supply Index (which accounts for snowpack, mountain precipitation, streamflow, reservoir contents, and soil moisture) has the Beaverhead and Red Rock watersheds rated as slightly dry. The driest areas of Montana continue to be the Sun, Teton, and Marias watersheds along the Rocky Mountain Front. The U.S. Drought Monitor rates these areas as suffering from D1 Moderate Drought.

As we would expect during our highest precipitation months of May and June, the 7-day forecast predicts around an inch of precipitation for most areas of Beaverhead County between May 7 and May 16. Areas of eastern Montana may receive around 3 inches of precipitation over the next week.

For more climate and water supply information, please check out the links below:

National Weather Service Presentation – May 2016 DTF Presentation

Bureau of Reclamation Water Supply Outlook – BOR Clark Canyon May WY16

May16 DTF