Henry’s Fork

Henry’s Fork, March 2nd, 2024

Yes, the current storms have limited access to much of the river and its drainage. But consider that this unusual amount of snowfall means better potential for great fly fishing next season.

Headlines  From Dr. Rob Van Kirk’s Henry’s Fork Drainage SWE Report Filed March 2nd

• Moderate and more widespread precipitation yesterday ended a very wet month of February, increasing water-year total precipitation to 96% of average and SWE to 82% of average.
• Heavy precipitation is expected to continue for the next week, with the March monthly outlook leaning toward above-average precipitation.
• Mean outflow from Island Park Reservoir over the critical December–February period for trout survival was 411 cfs, 116% of average.
• Island Park Reservoir gained 4,732 ac-ft over the Dec–Feb period and is 90% full, compared with 78% full on average. Outflow will be reduced to 375 cfs next week to fill the reservoir a little faster.
• The upper Snake River reservoir system is filling rapidly and is 83% full, compared with 66% full on average.

Details

As important as the warm temperatures may end up being later this spring for reservoir ice-off and subsequent water quality, the bigger story of February 2024 was precipitation. The watershed mean for the month was 5.18 inches, 142% of average. February precipitation totals were 127% of average in Fall River headwaters, 130% of average in Teton headwaters, 143% of average in upper Henry’s Fork, and a whopping 218% of average in the valleys. That moved water-year precipitation from 84% of average at the beginning of the month to 96% of average this morning, ranking 18th out of the last 36 years.

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, February 24th, 2024

This weekend looks like a good time to enjoy midge activity on the lower river before another stormy week begins on Monday. A bonus could be the first, but minor appearance of BWOs on the lower river. Consider that the rainbow trout spawning season is beginning. So lets allow them to do so in peace. It is in our best interests if we want his event to replenish their population for years coming up.

Headlines From Dr. Rob Van Kirk’s Snow-Water Equivalent (SWE) Report Filed 2/24 for the Henry’s Fork Drainage

Light precipitation yesterday kept the water year total at 96% of average and SWE at 81% of average.

• A major winter storm is still expected on Monday and Tuesday, with additional precipitation later next week.
• At an average outflow of 451 cfs, Island Park Reservoir dropped by 112 ac-ft yesterday and is 90% full, compared with 78% full on average.
• The upper Snake River reservoir system is filling rapidly and is 81% full, compared with 62% full on average.

Details

Natural flow stayed fairly constant yesterday at 96% of average: 91% in upper Henry’s Fork, 110% in Fall River, and 92% in Teton River. This is the largest difference between this year and 2016. Cumulative natural streamflow so far this water year over the Henry’s Fork watershed is 97% of average, ranking 25th out of the last 47 years (48th percentile–pretty close to the middle of the pack). On the other hand, natural flow at this point in water year 2016 was only 81% of average, ranking 42nd out of the 47 years.

So, while we know that warm late-winter and early spring temperatures cause poor water quality in Island Park Reservoir, we also know that natural streamflow into the reservoir counteracts that effect. Higher inflow produces better water quality. So, while climatic factors so far this winter look very much like 2016, the watershed is in much better shape this year than it was in 2016, thanks to above-average snow last year and to above-average precipitation in the late summer and early fall. The solid February we are having will also help. Lastly, water conservation measures implemented in 2018 by our agricultural partners, Fremont-Madison Irrigation District, and US Bureau of Reclamation have greatly reduced irrigation-season drawdown of Island Park Reservoir over the last six years, which will also help limit the negative effects of warm temperatures and low snowpack on Island Park Reservoir this summer.

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, February 17th, 2024

Headlines from Rob Van Kirk’s Henry’s Fork Drainage Snow-Water Equivalent (SWE) Report Filed Yesterday

• Heavy precipitation yesterday moved the needle substantially, as water-year total precipitation increased to 97% of average and SWE to 81% of average.
• Lighter precipitation will continue off and on for the next week.
• Natural flow increased to 102% of average yesterday due to very warm temperatures.
• At an average outflow of 465 cfs, Island Park Reservoir gained 111 ac-ft yesterday and is 91% full, compared with 77% full on average.

Details

In recent years, we have seen the month of February turn a below-average snowpack into an above-average snowpack. The most striking example was 2019, when SWE improved from 79% of average on January 31 to 121% of average on February 28. Could that happen this year? Probably not with respect to snowpack, although February may bring water-year total precipitation back up to average. Total precipitation for the first 15 days of February has exceeded the monthly mean already, so February will definitely be the first month of above-average precipitation since October and will likely rank in the top 10 for February precipitation. If we receive average precipitation for the rest of the month—which is very likely—the water-year total will stay at 97% of average. However, current outlooks give a decent chance of above-average precipitation late in the month, so we could end the month a percentage point or two higher with respect to average.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

  Why do we offer this information ?

Much of the SWE information Dr. Van Kirk collects then offers on the Henry’s Fork drainage impacts the water quantity and therefore angling quality of the upcoming season. And that quantity is determined mainly by the snow accumulation of the previous winter. The activity of the salmonid population and the availability of the aqueous forms on which they feed are impacted by the amount of water in which they live. The fly fisher benefits from this information with respect scheduling visits that will provide the best chance for a satisfying angling experience. The fly fishing retailer benefits through helping to decide when to offer items ( flies in particular) specific to the time of the season.

Henry’s Fork, February 10th, 2024

Midge hatches offer good top water fishing during pleasant mid days. Rainbow trout on the lower river are beginning their spawning mode. Please avoid disturbing any spawning fish as well as their redds.

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

• Precipitation focused in the upper Henry’s Fork yesterday increased water-year total precipitation for the watershed to 94% of average and SWE to 78% of average.
• Light precipitation is expected today, followed by relatively dry conditions for the next week.
• Natural flow stayed at 105% of average.
• At an average outflow of 430 cfs, Island Park Reservoir gained 48 ac-ft yesterday and is 91% full, compared with 76% full on average.
• The upper Snake River reservoir system is 77% full, compared with 62% full on average.

Details

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, February 3rd, 2024

The river below Ashton Dam is offering some excellent midge hatches during days without storms. Choose mid days of relatively warm ( air temps near or higher than 40 Deg. F.), wind-free and overcast days which offer the best hatches. Flow is near normal (1170 cfs) making wading not difficult while access is good. Any pattern simulating a midge cluster is sure to bring interest from resident trout.

Headlines from Dr. Rob Van Kirk’s Henry’s Fork Drainage Snow-Water Equivalent Report of “Ground Hog’s Day.”

• Maximum temperature yesterday set a record high for the date for the fourth consecutive day.
• Only very light precipitation was recorded, leaving water-year precipitation at 84% of average and SWE at 66% of average.
• Moderate to heavy precipitation is expected today through the end of next week.
• At an average outflow of 398 cfs, Island Park Reservoir dropped by 15 ac-ft yesterday and is 90% full, compared with 75% full on average.
• The upper Snake River reservoir system is 75% full, compared with 61% full on average.

Details

Yesterday’s watershed-averaged maximum temperature set a record high for the date for the fourth consecutive day. Very light precipitation was recorded, leaving the water-year total at 84% of average and snow water equivalent (SWE) at 66% of average. Current SWE is still third lowest for the date, ahead of 2001 and 1994.

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 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.