Henry’s Fork, March 30th, 2024

Major run-off has yet to reach the river as flows throughout are about normal for this time of the year. Based on Dr. Van Kirk’s information below, a greater than normal run-off could result from the high accumulation of snow in drainage streams originating in the Teton and Big Hole ranges and the southwest corner of Yellowstone Park. Look for run-off to begin as we warm in April and trout will hunker closer the bottom to pick off the abundance of drifting food forms. Right now on the lower river, BWOs and March brown mayflies and midges provide good top water fishing with best success during overcast days with little ( Is that possible?) wind. Presenting streamer, woolly bugger, and rubber leg patterns is also effective especially under these atmospheric conditions. Smaller nymph patterns drifted into holding water will also bring responses from resident salmonids. All this will change with the arrival of serious run-off. We will keep track of its progress to help with planning your fishing strategy.

Headlines from Dr. Rob Van Kirk’s SWE Report for the Henry’s Fork Drainage Filed March 29th

• Heavy precipitation yesterday increased the water-year total and SWE each two percentage points to 104% and 95% of average, respectively.
• Generally wet, cool weather is expected to continue for the foreseeable future.
• At an outflow of 449 cfs, Island Park Reservoir gained 354 ac-ft yesterday from precipitation and is 92% full, compared with 83% full on average.
• The upper Snake River reservoir system is 90% full and continuing to fill, despite 3500 cfs of diversion for managed aquifer recharge and 2500 cfs spill at Milner Dam.

Details

Mean temperature yesterday was right at average, and precipitation averaged 0.58 inch across the watershed, the highest one-day total since March 2. Precipitation heavily favored the upper Henry’s Fork sub-watershed and Yellowstone Plateau, where all five SnoTel stations in that area received at least 0.8 inch of water equivalent. White Elephant led all stations yesterday at 1.6 inches. Totals elsewhere in the watershed ranged from a few one-hundredths of an inch to 0.5 inch. This was enough to move the water-year total up two percentage points to 104% of average, ranking 12th out of the last 36 years (57th percentile).

New snow water equivalent (SWE) accumulations ranged from 0.2 inch at Grand Targhee and Pine Creek Pass to 1.7 inches at White Elephant. All stations in the Island Park/Yellowstone Plateau area received 0.9 inch or better. The day’s totals moved watershed-mean SWE up two percentage points to 95% of average, ranking 21st out of the last 36 years (43rd percentile). Current SWE is at its seasonal maximum at all nine stations. This ensures that annual peak SWE at Island Park will occur later than its statistical average, which is March 27. Average date of peak SWE at Pine Creek pass is March 30, and given current conditions and weather forecasts, this year’s peak SWE there will likely also occur later than average.