Henry’s Fork

Henry’s Fork, January 27th, 2024

Headlines From Dr. Rob Van Kirk’s Henry’s Fork Drainage Snow Water Equivalent Report of January 26th, 2024

• Repeat of Wednesday: light precipitation yesterday was enough to keep water-year total precipitation at 88% of average and SWE at 70% of average.
• Generally dry weather is expected until late next week, when we have a 50-60% chance of above-average precipitation and a 20% chance of heavy precipitation.
• At an average outflow of 377 cfs, Island Park Reservoir gained 28 ac-ft yesterday and is 90% full, compared with 74% full on average.
• The upper Snake River reservoir system is 73% full, compared with 60% full on average.

. Precipitation was enough to keep the water-year total at 88% of average: 88% in the Teton headwaters, 86% in Fall River headwaters, 81% in upper Henry’s Fork, and 129% in the valleys.

New snow water equivalent (SWE) accumulations were light, ranging from 0 at three stations to 0.3 inch at Grand Targhee. This left SWE at 70% of average: 77% in Teton, 74% in Fall River, and 61% in upper Henry’s Fork. The watershed mean stayed in 34th place out of the last 36 years, still ahead of 2001 and 1994 but behind 2010 and 1990. For a recent-year reference, current SWE is about 8% lower than it was at this time in 2021, which ended the winter with a peak SWE of 78% of average.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

Henry’s Fork, January 13th, 2024

Headlines from Rob Van Kirk’s Henry’s Fork Drainage SWE Report of January 12th, 2024

• Yesterday’s precipitation was relatively light, keeping the water year total at 82% of average. SWE increased to 62% of average but is still the lowest on record for the date.
• Light precipitation is expected here over the next few days, while low temperatures in the range of -20 degrees are expected tomorrow morning.
• At an outflow of 409 cfs, Island Park Reservoir gained 55 ac-ft yesterday, all due to snowfall on the reservoir surface. The three reservoirs in the Henry’s Fork are 90% full, compared with 79% full on average.
• The upper Snake River reservoir system is 69% full, compared with 57% full on average.

Details

Light precipitation is expected to continue off and on through the weekend here, with much heavier amounts to our south. Another round of slightly heavier precipitation is possible on Tuesday and Wednesday. The latest 7-day forecast shows a very strong northwest-southeast gradient in precipitation for our region, with only a few one-hundredths of an inch expected at the northwest corner of the watershed but up to 1.5 inches in the southeast corner. Meanwhile, up to 4 inches of water equivalent are expected in the Wasatch Mountains of Utah over the next week. Looking 1-2 weeks out, much warmer temperatures with near-average precipitation are expected. Long-term outlooks as well as historical records give us a high probability of ending the winter with a below-average snowpack. Near-record high snowfall would be needed over the remainder of the winter just to put us at average in mid-April.

 Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

208-652-3568 FAX

[email protected]

Henry’s Fork, January 6th, 2024

Details From Dr. Rob Van Kirk’s Henry’s Fork Drainage Snow-Water Equivalent Report Filed Yesterday

Headlines 1/5

• Light precipitation yesterday kept the water-year total at 80% of average and SWE at 57% of average.
• Precipitation is expected to continue for at least the next 10 days.
• At an outflow of 366 cfs, Island Park Reservoir gained 83 ac-ft yesterday and is 89% full, compared with 71% full on average.

Details are given below to reveal some concern for below normal amounts of snow throughout in the drainage so far this winter.

Unfortunately, no appreciable precipitation is indicated for at least the next week. Some very light precipitation is possible late next week, with high uncertainty in forecasts and outlooks beyond that. The general trend is still toward moderate to heavy precipitation to our south and dry conditions from here northward. Temperatures are expected to be above average, although inversions are keeping temperatures in the valleys a little lower than had been anticipated a few days ago.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

208-652-3568 FAX

[email protected]

Henry’s Fork, December 16th, 2023

Access remain good from Ashton Dam on downstream. Streamer and woolly bugger types are good bets for action with the middle of blue bird days being the only time for comfortable fishing. Make sure there are no holes in those waders!

Headlines from Dr. Rob Van Kirk’s Henry’s Fork Drainage Water Status Report Filed Yesterday

• Another dry day dropped water-year total precipitation to 102% of average and SWE to 76% of average, with no appreciable precipitation on the horizon.
• For the first two weeks of December, natural flow was 90% of average at Island Park and 89% of average at Ashton. Most other stream gages are affected by ice.
• At an average outflow of 400 cfs yesterday, Island Park Reservoir gained 56 ac-ft and is 88% full, compared with 67% full on average.

Details worth noting for the drainage

Unfortunately, no appreciable precipitation is indicated for at least the next week. Some very light precipitation is possible late next week, with high uncertainty in forecasts and outlooks beyond that. The general trend is still toward moderate to heavy precipitation to our south and dry conditions from here northward. Temperatures are expected to be above average, although inversions are keeping temperatures in the valleys a little lower than had been anticipated a few days ago.

With most stream gages affected by ice, accurate estimates of natural stream flow are not possible on Fall River and Teton River. In the upper Henry’s Fork, natural flow over the first two weeks of December was 90% of average at Island Park and 89% of average for the whole subwatershed, measured at Ashton. Streamflow in the Buffalo River was 98% of average, although the gage record there is not as consistent as it as at other locations. In any case, natural flow—while much better than it was last year at this time—is still below average in the upper Henry’s Fork.

Together, the three reservoirs in the Henry’s Fork watershed are 88% full, compared with 75% full on average. The upper Snake River reservoir system is filling faster than average and is 61% full, compared with an average of 52% full for the day.

Dr. Rob Van Kirk

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

[email protected]

Henry’s Fork, December 2nd, 2023

Headlines From Dr. Rob Van Kirk’s Henry’s Fork Drainage Water Status Report Filed on November 30th.

• Another dry day dropped water-year precipitation to 93% of average and SWE to 49% of average, as we await a large winter storm forecast to arrive in the watershed late tonight.
• At an average outflow of 226 cfs, Island Park Reservoir gained 395 ac-ft yesterday and is 86% full, compared to 63% full on average.
• Outflow from Island Park Reservoir will be increased by roughly 165 cfs tomorrow.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

208-652-3568 FAX

[email protected]

Upper river has water cold enough to slow fishing, and access is becoming tougher each day.

For the lower river access is better but hours on blue-bird days (midge activty and nymphing) are the only time for comfortable fishing.

Henry’s Fork, November 28th, 2023

Headlines from Dr. Rob Van Kirk’s Henry’s Fork Drainage Water Status Report Filed Yesterday

• The Thanksgiving storm stayed to our south, leaving us with only 0.12 inch of precipitation.
• Water-year total precipitation is 99% of average this morning, the first time it has been below average this water year.
• Natural flow has dropped very slowly over the past week and was 92% of average yesterday.
• At an average outflow of 228 cfs, Island Park Reservoir has gained 364 ac-ft/day over the past week and is 85% full, compared to 63% full on average.
• Current reservoir volume is equal to the April-10 average.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

[email protected]

• Access remains good on the river below Ashton Dam, however water temps are dropping to a level that impact fish activity. Brown trout are still in a spawning mode, so streamer patterns of choice are still effective, with middle of the day being best time to fish. Same applies to sporadic midge hatches. Presenting nymph patterns of choice can be effective.

Henry’s Fork, November 21st, 2023

Headlines from Dr. Rob Van Kirk’s Henry’s Fork Drainage Water Status Report filed Yesterday,11/20

• Light precipitation fell over the weekend as expected; the water-year total is 117% of average.
• Another round of very light precipitation is expected on Thanksgiving Day, and long-term forecasts call for continued dry conditions.
• After flattening out for a few days, natural flow increased a little yesterday in response to precipitation.
• At an average outflow of 230 cfs, Island Park Reservoir gained 472 ac-ft/day over the past three days and is 84% full, compared to 61% full on average.

BWO activity is quickly diminishing on the entire river. It will return to significance sometime next March depending on weather and water conditions, Midge activity remains throughout the year, and under the right conditions can be almost massive at times. So we are entering the time when nymph and streamer patterns are most effective on the entire river.

Henry’s Lake, November 18th, 2023

Bets are that Henry’s Lake will ice over this coming week with colder and unsettled weather coming! So we had a longer season this year for wading and boating than last year.

Henry’s Fork, November 13th, 2023

Fun Farm Bridge at Dusk

This great weather will not last much longer, so get out and enjoy. Daytime hours are not only pleasant, but hold the best BWO and midge activity making their life cycle patterns a must for the fly box. Next week looks like normal November conditions will prevail.

One of the best happenings on the river is that aquatic vegetation has broken away giving more “fishable” water and a better chance for landing that big fish ( no weeds to bury into). Fly rod jigs are a good bet for streamer action with fish now concentrated in deeper water up and down the river. Plunk one into the top of any deep waters, let it sink and drift a bit, then retrieve with a “jigging motion” to make it rise and fall in the water column.

Headlines From Dr. Rob Van Kirk’s Henry’s Fork Drainage Water Status Report Filed Yesterday.

• Last week was warm and dry, dropping water-year precipitation to 134% of average.
• Generally dry conditions are expected to continue this week.
• Natural flow continues to drop from its November 3 peak, but rate of recession has dropped to around 2% per day.
• At an average outflow of 226 cfs yesterday, Island Park Reservoir gained 448 ac-ft and is 81% full, compared to 58% full on average.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

208-652-3568 FAX

[email protected]

Henry’s Fork, November 11th, 2023

What applies to the South Fork with respect to fishing strategy much applies to the river below Ashton Dam. For the upper river streamers and double nymph rigs work best in such as Box Canyon and the Tubs. Flow is down ( about 200 cfs) in Box Canyon to the point that hard sided boats have a tough time avoiding its emerging structure. Day time is best for top water fishing and is comfortable as long as nice weather prevails. Remember that the fishing season in Harriman State Park closes on November 30th.