Henry’s Fork, February 9th, 2021

February 9, 2021

Are you interested in doing a trip to fish the upper Henry’s Fork and drainage during the upcoming season? Would seeing how snow and water conditions appear to be stacking up to help in planning? The information Dr. Rob VanKirk compiles may help. Rob’s analyses, and reports on water and snow conditions is as good as it gets. Below is Rob’s latest update.

Henry’s Fork Water Supply, Feb 09 2021

Headlines:

After a dry day, water-year precipitation is 84% of average, and SWE is 85% of average.
Island Park Reservoir gained 112 ac-ft yesterday, typical of fill on recent dry days.
The reservoir is 87% full, compared with 75% full on average.
Weather forecasts continue to lean more toward wetter, warmer conditions and away from the extreme cold forecast last week.

Details:

At 6 degrees F below average, yesterday was the coldest in 13 days. Only a trace of precipitation was recorded, leaving the water-year total at 84% of average. Snow water equivalent (SWE) dropped a percentage point to 85% of average. After declining steadily since last July, the three-year average watershed precipitation appears to have bottomed out in the past two weeks and should increase a bit over the next few weeks, if precipitation forecasts prove to be accurate. This index of long-term watershed conditions is just a hair above average right now.

Forecasts are still uncertain about the details of weather over the next week but continue to gain confidence in warmer, wetter conditions than were forecast last week. Very cold air is expected to stay just on the other side of the Continental Divide, leaving us on the warm, wet side. “Warm” is relative, as temperatures are likely to be near average for the next week, a few degrees colder than last week. Regardless of temperature, snow is certain on Thursday and Friday and likely again early next week. The 7-day forecast calls for 0.25 inch across the lower elevations and up to 3 inches at the southern end of the Teton Range. As was the case last week, precipitation will favor the southeastern corner of the watershed. If forecast amounts materialize, SWE in Fall River and Teton River subwatersheds will improve to 90-92% of average by this time next week. SWE in the upper Henry’s Fork will remain at or below 80% of average.

Island Park Reservoir gained 112 ac-ft yesterday, typical of fill rate on dry days. The reservoir is 87% full, compared with 75% full on average. The reservoir will reach the April-1 target of 120,000 ac-ft around March 1.

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