Streamflow, Drought, and Water Supply Conditions

Water supply conditions as of 6/20/2018

From Jacqueline Knutson, Hydrologist, Montana Fish, Wildlife and Parks

Snowpack: The Big Hole Basin is at 113% of average; the Jefferson Basin is at 115% of average. Snowmelt this year started earlier than normal and has been rapid since it began. As we move forward into summer, this could be of concern. The promise of a record-setting snowpack delivering abundant water supply through the summer could easily turn into record-setting flows for a few months, and water shortages later in the summer much like last year. Snow disappeared rapidly in May with lots of sunshine and warm temperatures. There is still some snow at the highest elevations but the mid and lower elevation sites cleared out quickly in May. Darkhorse Lake has 29 inches of snow and 13 inches of snowater equivalent which is just below average for this date. What was shaping up to be a strong snowpack through the early summer has left us and we’re basically back to the same situation we were in this time last year. Therefore, the rest of this summer’s water season is going to rely heavily on precipitation events and our weather, rather than snowpack, will make or break river flows through the summer.

Precipitation: May precipitation was below average in most of the Jefferson Basin although along the divide there were a few spots that recorded above average precipitation. The story in May was that precipitation was very hit-or-miss. There were plenty of sunny days and early June has followed that pattern, although the last few days have been a departure from the sunshine. The Bloody Dick SNOTEL station has received 0.90 inches of rain in the last two days and some sites in Beaverhead County have seen over 2 inches of rain in the last 5 days. This has certainly benefited streamflows but precipitation is expected to be below normal for the rest of the month and into the summer.

Temperatures: A strong ridge of high pressure built up over most of the western United States this May and Montana felt the effects with above normal temperatures the entire month. Statewide, it was the warmest May since 1958.

Period of Record Monthly Climate Summary – Period of Record : 01/01/1923 to 06/09/2016

See details below from Western Regional Climate Center:


Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual
Average Max. Temperature (F) 26.4 31.1 38.5 49.2 60.3 68.6 79.4 77.8 67.6 55.0 38.0 28.0 51.7
Average Min. Temperature (F) 1.2 3.3 10.8 21.2 28.7 36.1 38.2 34.7 27.8 21.3 12.3 3.6 19.9
Average Total Precipitation (in.) 0.70 0.52 0.74 0.95 1.64 1.96 1.09 1.03 0.99 0.83 0.76 0.77 11.97
Average Total SnowFall (in.) 11.8 8.3 8.6 4.5 2.5 0.5 0.0 0.0 0.5 1.9 7.8 10.8 57.0
Average Snow Depth (in.) 9 10 8 1 0 0 0 0 0 0 2 5 3

Percent of possible observations for period of record.
Max. Temp.: 98.7% Min. Temp.: 98.6% Precipitation: 98.6% Snowfall: 76.4% Snow Depth: 50.3%


National Water Supply Reports

Nation-wide information for water supply and climate prediction & forecasts. 

National Weather Service Climate Prediction Center – Three Month Outlook Report


Montana Water Supply Reports

Statewide information for water supply and drought conditions. Report breaks out conditions by major basins:

Montana Water Supply Outlook Reports (March 2018)

Guide to Using the New Montana Water Supply Report

Water supply and drought condition information specific to the Upper Missouri Basin:

Upper Missouri River Basin Water Supply Report: Spring 2017

Water Monitoring Resources from the Montana Watershed Coordination Council

Montana Watershed Coordination Council Water Monitoring Webpage


Past Streamflow & Snowpack Reports

April 2018 Streamflow/Snowpack Report (PDF)

March 2018 Streamflow/Snowpack Report (PDF)

February 2018 Streamflow/Snowpack Report (PDF)

November 2017 Streamflow/Snowpack Report (PDF)

October 2017 Streamflow/Snowpack Report (PDF)

August 2017 Streamflow/Snowpack Report (PDF)

June 2017 Streamflow/Snowpack Report (PDF)

April 2017 Streamflow/Snowpack Report (PDF)

March 2017 Snowpack Report (PDF)

February 2017 Snowpack Report (PDF)

November 2016 Streamflow/Snowpack Report (PDF)

September 2016 Streamflow/Snowpack Report (PDF)

May 2016 Streamflow/Snowpack Report (PDF)

April 2016 Streamflow/Snowpack Report (PDF)

March 2016 Streamflow/Snowpack/CCAA Report (PDF)

February 2016 Streamflow/Snowpack Report (PDF)