Big Hole River Conditions & Drought Management Plan

From Jacqueline Knutson, Montana Fish, Wildlife and Parks Hydrologist. As of 6/19/2019:

Streamflows: Seasonal gages are below average at every site in the watershed except for the gage at Glen (which has some interesting “painting” data which may be impacting accuracy). In the CCAA management sections we have come within the seasonal Grayling flow targets in two management sections already; although weather and irrigators helped us bump back above flow targets before calls had to be made. The gage at Saginaw was completely replaced this spring and has been reporting since the replacement. This weekend looks to continue the cool and wet weather we’ve seen the past two weeks but is expected to taper off and we may see continued drops in flows if warm and dry weather return and the water supply system shifts from snowpack driven to precipitation driven. Streamflow forecasts for the April 1^st – July 31^st period are below average for the Big Hole River so please keep an eye on forecasts and be ready for potential shortages if July precipitation is sparse once again.

Snowpack: At this time the Big Hole Basin is at 100% of average. The Jefferson Basin in its entirety is at 99% of average but remember that that average is based on snowpack on this day exactly; 100% of not a lot is still not a lot and the surrounding basins are now free of snow. The water supply forecast doesn’t look great for the Big Hole this summer and we will certainly be hoping for favorable (wet) weather patterns for the rest of June through the irrigation season.

Precipitation: Precipitation was below average in the southwest corner of Montana in May. The Jefferson basin saw 86% of its average May precipitation. We continue the pattern of productive precipitation followed by a dry spell. With no major changes in the long range forecast I imagine this will continue through the summer to some extent. This will be important as our water supply will depend on receiving normal precipitation from now until August to avoid water shortages toward the end of the irrigation season.

Temperatures: May temperatures were generally average throughout the state although we were a little closer to above average on the western side of Montana. This did nothing to slow snowmelt this season and we are ahead of schedule. The slow down in our melt (and the reason that we are still average for our remaining snowpack) came in the third week of May but we rapidly caught back up with warmer temperatures the last week of May and in early June.

Forecast: El Nino continues to be present and is expected to persist (66%) through the rest of the summer. The odds of El Nino lasting through the fall and early winter is lowering, now down to 50-55%. I expect, then, that the weather patterns that we’ve been seeing this El Nino will continue with warmer temperatures and average precipitation coming in to replace some of the cool weather we’ve had the last month or so.

The three-month outlook currently favors above average precipitation and a continuation of the above average temperatures we’ve seen over the last few months now. These outlooks will be updated at the end of the week and I recommend that people take a look at these as they get updated.