Henry’s Fork

Henry’s Fork, November 23rd, 2021

Snow shoes or X-country skis will help if you intend to fish the river in Island Park! Nymph patterns, large and small, and streamer patterns will be best candidates for action here and in the lower river as well.

There is near global interest in how 2021-2022 winter snowfall/water conditions will impact next season’s fishing conditions in the Henry’s Fork drainage.

Through the upcoming winter we therefore will post the Henry’s Fork Foundation’s Dr. Rob Van Kirk’s weekly summary of these conditions. Information from Dr. Van Kirk’s summary prepared on November 22nd follows.

Headlines:  

• Yesterday was warm and dry, and with the exception of a little snow today and tomorrow, warm and dry conditions will continue for the next week.
• Natural flow dropped yesterday in response to a cold morning and is 78% of average.
• At a mean outflow of 119 cfs, Island Park Reservoir gained 481 ac-ft yesterday and is 66% full, compared with 61% full on average.

Details:

Despite a cold start to the day, mean temperature yesterday was 3 degrees F above average. No precipitation was recorded. Except for some light snow today and tomorrow, generally warm and dry conditions are forecast for the next week. Precipitation is tentatively forecast to return in the middle of next week.

Natural flow decreased a little yesterday as a result of cold overnight low temperatures. River icing was apparent in the Fall River hydrograph yesterday. Watershed-wide natural flow was 78% of average yesterday and within a few percentage points of that in each of the three subwatersheds. Cumulative natural flow for the water year so far is 77% of average.

At an average outflow of 119 cfs, Island Park Reservoir gained 481 ac-ft yesterday and is 66% full, compared with 61% full on average. At the current outflow, reservoir gain due to stream inflow has been in the range of 475-500 ac-ft/day. Direct precipitation on the reservoir surface has added an additional 1000 ac-ft since the start of the water year, equivalent to an additional 10 cfs of inflow, on average.

: Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-652-3567 OFFICE

208-881-3407 CELL

208-652-3568 FAX

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Henry’s Fork, November 9th, 2021

Streamers and nymph patterns are the ” Name of the Game” up and down the river now.

All of us are interested in what upcoming winter snowfall and water situations will be for the Henry’s Fork drainage. Such information can provide likely water conditions during the next angling season. Thus we will continue reporting what information Dr Rob Van Kirk assembles each week on the drainage water conditions. Information Rob offers from his Monday,November 8th report follows.

Headlines:  

• Yesterday’s mean temperature was the coldest since March 31, and some precipitation lingering from the weekend was recorded very early yesterday morning.
• Natural flow has dropped a little over the past day or two to 73% of average for the date.
• At a mean outflow of 120 cfs, Island Park Reservoir gained 473 ac-ft yesterday and is 60% full, compared with 57% full on average.
• Above-average temperatures and near- to above-average precipitation are expected to continue.

Details:

Yesterday’s mean temperature was the lowest since March 31, although it wasn’t even all that cold, at 3 degrees F below average. A little precipitation leftover from Sunday was recorded very early yesterday morning at a few locations in the northern and eastern areas of the watershed. Snow accumulation so far this fall remains below average, despite above-average precipitation. At least for now, the combination of warm temperatures and above-average precipitation is favorable to increase soil moisture prior to the inevitable arrival of widespread freezing temperatures and snow accumulation. In general, temperatures are expected to remain at or above average, and near- to above-average precipitation is also expected to continue.

Watershed-total natural flow has dropped a little over the past day or two and is 73% of average for the date and 75% of average for the water year so far.  

At an average outflow of 120 cfs, Island Park Reservoir gained only 473 ac-ft yesterday on a day without precipitation. Over the weekend, a substantial fraction of reservoir fill was due to direct precipitation on the reservoir. Precipitation forecast over the next week will add around 250 ac-ft over and above that due to stream inflow. The reservoir is 60% full, compared with 57% full on average.

G

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-652-3567 OFFICE

208-881-3407 CELL

208-652-3568 FAX

Henry’s Fork, November 6th, 2021

Just about anywhere on the lower river brown trout are on the move. Presenting big streamer and woolly bugger patterns are the best way to encounter them.

Henry’s Fork, November 2nd, 2021

Presenting streamer patterns in deeper waters throughout the river is becoming very effective.

Excerpts from Dr. Rob Van Kirk’s Monday analysis of water conditions in the Henry’s fork drainage are below

Headlines:  

• The first month of water year 2022 was a little on the warm side but wet, with 140% of average precipitation.    
• Natural flow has dropped steadily since last Wednesday’s rain-driven peak and is 80% of average.
• At a mean outflow of 116 cfs, Island Park Reservoir has gained 535 ac-ft/day over the past three days and is 57% full, compared with 54% full on average.

Details:

Mean temperature for the month of October was 1 degree F above average, due primarily to consistently warm daily minimum temperatures over the last 12 days. The warm overnight lows have accompanied generally high humidity (for around here, anyway) and persistent precipitation, at least in some locations. For the month as a whole, precipitation was 140% of average. By subwatershed, monthly totals relative to average were 149% in Fall River headwaters, 144% in upper Henry’s, 136% in the Teton headwaters, and 120% in the valleys. The only station with below-average precipitation during the month was Ashton, coming in at 93% of average. Warm temperatures prevented much snow accumulation, despite above-average precipitation. The only two stations with appreciable snow water equivalent on the ground right now are the two highest in elevation: Grand Targhee at 81% of average and Black Bear at 67% of average.

Over the first month of the new water year, the three-year average watershed precipitation increased by almost 1 inch but remains 1 inch below average. One-year accumulated moisture availability in the agricultural areas increased 2.5 inches but remains 4.5 inches below average. New outlooks for the month of November issued yesterday give our area better-than even odds of continued warm temperatures, above-average precipitation, and slow improvement in drought conditions. In the short term, light to moderate precipitation is expected tonight/tomorrow morning and again Thursday night/Friday morning. Forecast confidence is low after that.

Watershed-total natural flow has dropped steadily since Wednesday’s rain-drive peak and was 80% of average yesterday. Accumulated natural flow for the water year so far is 77% of average, compared with 76% of average for the entirety of water year 2021 and only 69% of average for April-September. Diversion stayed fairly constant near the long-term average over the weekend but will decrease today as canals shut down after the end of administrative irrigation season 2021. Based on data available to date, diversion was 92% of average for irrigation year 2021. That figure may change a little once Water District 1 adds data from pumps that are not measured in real time and adjusts data for rating-curve shifts. The process of approving all diversion and water-rights accounting data for the previous irrigation year is usually completed in early March, but at the watershed scale, the approved data are usually not much different than data available at this point.

We measured outflow from Island Park Reservoir at 122 cfs on Friday, right on the trajectory determined by measurements over the previous two weeks. Mean outflow since Friday was 116 cfs, at which the reservoir gained 535 ac-ft/ day. The reservoir is 57% full, compared with 54% full on average. Total storage in three reservoirs in the Henry’s Fork watershed is 68% of capacity, around 630 ac-ft above average for the date.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-652-3567 OFFICE

208-881-3407 CELL

208-652-3568 FAX

Henry’s Fork, October 30th, 2021

On the lower river, Box Canyon, Cardiac Canyon holes and runs deep, and the Tubs, presenting streamer patterns is the name of the game. If you favor top water fishing, BWO life cycle patterns provide the best action.

More information from Dr, Rob Van Kirk on Henry’s Fork drainage water status follows.

Headlines:  

• Precipitation yesterday was moderate and widespread again yesterday, averaging 0.4 inches across the watershed.    
• Natural flow has increased by 330 cfs (17%) since Friday and is 89% of average.
• At a mean outflow of 124 cfs, Island Park Reservoir gained 781 ac-ft yesterday, 110 of which was due to direct precipitation on the reservoir surface. The reservoir is 55% full, compared with 53% full on average.

Details:

Moderate precipitation continued yesterday at all locations, averaging 0.4 inch across the watershed. Precipitation was uniformly distributed across the watershed, and even valley areas received 0.2-0.3 inch. This pushed the water-year total to date to 3.63 inches, compared with the long-term average of 2.75 inches for the whole month of October. Temperatures dropped yesterday to 2 degrees F below average, the coolest in 11 days. As a result, most of the SnoTel stations gained new snow water equivalent (SWE) yesterday. White Elephant, Black Bear, and Grand Targhee each have over 1 inch of SWE on the ground. Small chances of precipitation continue on and off over the next week, with temperatures staying near average.

Watershed-total natural flow has increased by 330 cfs (17%) since Friday, with most of that increase occurring Monday and yesterday. Although streamflow in headwater areas peaked yesterday, some of that is still making its way to the lower watershed this morning. Natural flow yesterday was 89% of average for the date, and cumulative natural flow for the water year to date has increased a percentage point to 75% of average. Diversion incidentally increased by around 30 cfs yesterday due to higher river stage and was 93% of average. Total diversion for the irrigation year to date—which ends on Sunday—is 92% of average.  

At an average outflow of 124 cfs, Island Park Reservoir gained 781 ac-ft yesterday. Around 110 ac-ft of that gain was due to direct precipitation on the reservoir surface. The reservoir is 55% full, compared with 53% full on average. Over the next day or two, fill rate will gradually drop back to around 550 ac-ft/day, where it was prior to the recent precipitation event.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-652-3567 OFFICE

208-881-3407 CELL

208-652-3568 FAX

[email protected]

Henry’s Fork, October 26th, 2021

As is our usual practice, excerpts from Dr. Rob Van Kirk’s Monday AM analysis of the Henry’s Fork drainage water status are given below.

REPORT NOTE: USBR data sites are down for maintenance this morning, so diversion, streamflow and reservoir data are current only through Saturday. I’ve filled in missing data for USBR weather stations with data from the nearest non-USBR stations.

Headlines:  

• Precipitation during the much-anticipated atmospheric river event has so far been highly variable, ranging from a few hundredths in the valleys to over 1 inch in the Centennial Range.    
• Diversion and natural flow were around 75% of average until rain increased natural flow in Fall River on Saturday.
• At a mean outflow of 110 cfs, Island Park Reservoir gained 549 ac-ft/day for the week ending Saturday and is 54% full, compared with 52% on average.

Details:

Mean temperature last week was 3 degrees F above average. At 8 degrees F above average, Friday was the warmest day since October 6. Precipitation for the week-—most of which has fallen in the past two days—was highly variable across the watershed, ranging from a few hundredths in the valley locations to 1.3 inches at White Elephant. The Centennial Range and Yellowstone Plateau areas have received by far the highest totals thus far during the much-anticipated atmospheric river event that is bringing heavy precipitation to most areas of the West. Lewis Lake Divide, Black Bear, White Elephant and Crab Creek all received over 0.6 inch of water equivalent last week. Because of warm temperatures, new snow accumulation has been limited to the highest elevations, where Black Bear and Grand Targee have 1.7 inches and 2.5 inches, respectively, of snow water equivalent on the ground–around 80% of average for the date. Precipitation is expected to continue today and tomorrow, with somewhat cooler temperatures arriving this afternoon.

Watershed-total natural flow and diversion stayed around 75% of average until rain on Friday night and Saturday morning increased streamflow in Fall River by 40 cfs or so. Streamflow in the Teton River is also increasing a bit this morning.

We measured outflow from Island Park Reservoir at 114 cfs on Friday. For the week ending Saturday, mean outflow was 110 cfs, and the reservoir gained an average of 549 ac-ft/day. Projecting that gain through the end of yesterday, the reservoir is 54% full, compared with 52% full on average.   

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-652-3567 OFFICE

208-881-3407 CELL

208-652-3568 FAX

Henry’s Fork, October 23rd, 2021

With the stormy weekend and first of next week predicted, brown trout will be active on the lower river, so break out those streamer patterns. Other than that BWO activity will be plentiful anywhere on the river. For the river in Island Park, the best news is that Highway 20 repaving between the Sheep Falls Road and Riverside Campground is complete, so no more flaggers and long lines of vehicles to slow down traffic.

Henry’s Fork, October 19th, 2021

Aquatic weeds are breaking up everywhere giving better chances for landing larger fish especially on using finer tippets when presenting BWO, mahogany dun or midge life cycle patterns. Wherever you try the river, streamer patterns are a must. Brown trout are moving in the lower river, and locations in the upper river such as Box Canyon, Cardiac Canyon holes and runs, and The Tubs now host large foraging trout.

Below are excerpts from Dr. Rob Van Kirk’s summary of water conditions up to this morning in the Henry’s Fork drainage.

REPORT NOTE: I will be presenting a brief summary of water year 2021 at the Henry’s Fork Watershed Council meeting tomorrow, following a presentation on upper Snake River reservoir operations by the US Bureau of Reclamation. The meeting starts at 9:00 a.m., and you can join via Zoom at https://us02web.zoom.us/j/81474786741

Headlines:  

• Last week was cool and wet, putting us in a good position to receive above-average precipitation for the first month of water year 2022.  
• Natural flow has dropped a little from the effects of last week’s precipitation and is 75% of average.
• At a mean outflow of 110 cfs, Island Park Reservoir gained 592 ac-ft/day last week and is 51% full, compared with 50% on average.

Details:

Mean temperature last week was 7 degrees F below average, and precipitation totaled over 1 inch for the watershed. All stations received precipitation over the week, ranging from 0.02 inch at Ashton to 2.6 inches at Lewis Lake Divide. Total watershed precipitation for the water year to date is 2.10 inches, and with more on the way, the first month of water year 2022 will very likely receive above-average precipitation. That happened in only four months during water year 2021. Precipitation this evening is now forecast to be lighter than anticipated a few days ago, with most areas receiving 0.1-0.2 inch. However, very heavy precipitation is expected next weekend and into the beginning of next week. Totals over the next week are expected to range from 0.75 inch at the western edge of the watershed to as much as 2.5 inches along the Teton crest. Temperatures will generally remain near to slightly above average over that time period, but snow will continue to accumulate at elevations above 7,500 feet.   

Natural flow has dropped a little from the effects of precipitation early last week and is 75% of average across the watershed and within a few percentage points of that in each of the three subwatersheds. Accumulated natural flow for the water year to date is 74% of average. Diversion is still on a generally downward trajectory with two weeks remaining in the administrative irrigation year. 

At a mean outflow of 110 cfs, Island Park Reservoir gained an average of 592 ac-ft/day last week and is 51% full, compared with 50% full on average. The upper Snake River reservoir system is at 14% of average and filling slowly.  

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-652-3567 OFFICE

208-881-3407 CELL

208-652-3568 FAX

Henry’s Fork, October 12th, 2021

The challenge now will be getting to the river to fish especially in the Island Park area! October storms like this has happened before, and after it passes a lot of good fishing will remain. BWO and midge activty will offer top water fishing and presenting streamer patterns will become increasingly effective. Another “plus” coming from this weather is that it will help clear aquatic vegetation ffom All waters.

Here are excerpts from Dr. Rob Van Kirk’s update for today on water conditions in the Henry’s Fork drainage. There is some welcome info here to begin the water storage year.

Headlines:  

• The current winter storm over our area is over-achieving, producing 0.55 inch of water equivalent watershed-wide and the coldest temperatures since April.
• Natural flow dropped a little yesterday in response to colder temperatures, as yesterday’s precipitation fell as snow at all elevations.
• At an outflow of around 125 cfs, Island Park Reservoir gained 662 ac-ft yesterday, 100 of which was due to direct precipitation on the reservoir surface. The reservoir is 48% full and equal to the 1978-2021 average.

Details:

Precipitation yesterday exceeded expectations, with even more falling after midnight and continuing this morning. Through midnight, water-equivalent totals ranged from 0.02 inch at Ashton to 1.4 inches at Lewis Lake Divide, with a watershed average of 0.55 inch. Mean temperature yesterday was 32.8 degrees F, 6 degrees below average and the coldest since April 20. Precipitation fell as snow at all elevations, and all SnoTel stations are reporting snow on the ground this morning, ranging from 0.2 inch to 1.7 inches of water equivalent. Snow is expected to continue on and off through Thursday, with Friday morning’s low temperatures well down into the teens in most locations. Dry weather with a slow warming trend is expected over the weekend, which will melt most snow at the low and mid-elevations. Above-average temperatures are expected next week.

Natural flow dropped a little yesterday to 75% of average due to colder weather. Meanwhile, diversion dropped by nearly 100 cfs yesterday, so supply now exceeds demand by over 1100 cfs, the highest it has been since early June.

At an outflow of around 125 cfs, Island Park Reservoir gained 662 ac-ft yesterday, nearly 100 ac-ft of which was due to direct precipitation on the reservoir surface. The reservoir is 48% full and only 118 ac-ft below average for the date. However, the upper Snake River reservoir system as a whole continues to draft and is only 9% full.

As a final note this morning on streamflow at both Ashton and Island Park, which are critical to natural-flow calculations, I suspect that the current gaged flow at Ashton is lower than actual flow and that my estimate of Island Park flow based on our measurement last Friday is a little high. We will measure flow at both locations this Friday to get better estimates. Changes in the stream gage rating curves are large relative to actual flow in the river right now, as aquatic vegetation is decaying quickly and moving out of the stream channel.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-652-3567 OFFICE

208-881-3407 CELL

208-652-3568 FAX

Henry’s Fork, October 9th, 2021

It’s time to present your favorite streamer patterns anywhere on the lower river. The same can be said for The Tubs area above Mack’s Inn, Box Canyon, and any deep holes you can find in Cardiac Canyon.