Henry’s Fork

Henry’s Fork, January 3rd, 2023

Headlines from Dr. Rob Van Kirk’s SWE (snow-water equivalent) report for the Henry’s Fork Drainage filed yesterday are below.

Headlines:

• Mean temperature for the month of December was near average, but precipitation was 18% above average.
• Water-year precipitation to date is 113% of average, and SWE is 119% of average.
• Light to moderate precipitation is expected over the next week, with near-average precipitation forecast for the month of January.
• At an average outflow of 204 cfs, Island Park Reservoir gained 329 ac-ft/day over the last four days and is 71% full, 900 ac-ft ahead of average for the date.

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

Henry’s Fork, December 20th, 2022

Here are details from Dr. Rob Van Kirk’s SWE report this AM for the Henry’s Fork drainage.

Note the waning he gives for weather conditions the next several days.

Mean temperature yesterday was 5 degrees F below average. Only very light precipitation was recorded, dropping the water-year total to 109% of average and snow water equivalent (SWE) to 117% of average. The latest precipitation forecasts are a little wetter than yesterday’s, now calling for up to 2 inches of water equivalent along the Teton crest from today through next Monday. Potentially heavy snow remains possible early next week.

In the meantime–for those who live or are considering traveling here over the next few days–an extremely strong cold front is expected to pass through the area tonight and early tomorrow morning, bringing 40+ mph winds and widespread blowing snow. Following the front, temperatures will drop well below zero on Thursday morning. If forecasts hold, the upcoming cold temperatures will be the lowest we have seen since December 2016. Travel is not advised and will not even be possible in some places tomorrow and Thursday.

Where stream gages are still reporting, natural flow is still in the 70-75% of average range, where it has been since September.

At an average outflow of 193 cfs, Island Park gained 309 ac-ft yesterday, staying well ahead of the fill rate needed to meet the reservoir volume target at ice-off, which occurs in late April on average. The reservoir is 68% full, only 376 ac-ft below 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

Henry’s Fork, December 13th, 2022

Here is some great news from Rob Van Kirk’s Monday, December, 12th Henry’s Fork drainage SWE (snow-water equivalent) report.

Headlines:

• Precipitation over the past three days increased the water-year total to 124% of average and SWE to 145% of average.
• Since outflow from Island Park Reservoir was increased last Thursday, the reservoir has gained 344 ac-ft/day and is 64% full, compared with 65% full on average.

Details:

Precipitation over the past three days ranged from 0.04 inch at Alta to 1.3 inches at Grassy Lake and averaged 0.62 inch for the watershed. That increased water-year precipitation to date to 124% of average and snow water equivalent (SWE) to 145% of average for the date. SWE at all SnoTel stations is in the top one-third of water years since 1989. Generally wet, cold weather is forecast for the foreseeable future.

Since outflow from Island Park Dam was increased to around 195 cfs last Thursday, the reservoir has gained an average of 344 ac-ft/day. Around 75 ac-ft of that has been due to direct precipitation on the reservoir surface. The reservoir is 64% full and within 900 ac-ft of average for the date.

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

Henry’s Fork, November 8th, 2022

Looks like skis or snowshoes are now standard equipment for fishing much of the Henry’s Fork

Headlines:  from Dr. Rob Van Kirk’s Henry’s Fork drainage snow-water analysis report of today.

• Precipitation averaged 0.77 inch across the watershed yesterday, favoring the Ashton/Fall River area.
• New SWE ranged from 0.5 inch to 1.5 inches; the watershed total is over two times average for the date.
•  At an outflow of 128 cfs, Island Park Reservoir gained 717 ac-ft yesterday and is 55% full, compared with 57% full on average.

Details:

Precipitation yesterday materialized as forecast. Station totals ranged from 0.33 inch at Rexburg to 1.4 inches at Black Bear SnoTel. The heaviest amounts fell in the Ashton/Fall River area. The watershed average was 0.77 inch, increasing the water-year total to 137% of average. All SnoTel stations received new snow water equivalent. Current SWE is the highest for the date in the 1989-2022 record at Lewis Lake Divide, Pine Creek Pass, and Island Park. Watershed total SWE is over two times the average for the date. An additional 0.25-1 inch of water equivalent is expected over the next two days, before cold, dry weather settles in later in the week.

Natural flow increased yesterday in response to a rain/snow mix early in the day and was 81% of average yesterday.

At an average outflow of 128 cfs, Island Park Reservoir gained 717 ac-ft yesterday, 200 of which was from direct precipitation on the reservoir surface. The reservoir is 55% full, compared with 57% 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

Henry’s Fork, November 1st, 2022

Headlines from Dr. Rob Van Kirk’s water status report of yesterday for the Henry’s Fork drainage:  

• With the first month under our belt, water year 2023 started right where 2022 left off: slightly warmer than average, precipitation at 91% of average, and natural stream flow among the lowest on record.
• The first very cold weather of the fall arrives tomorrow, and heavy precipitation is expected to begin Saturday and last well into next week.
• At an outflow of around 130 cfs, Island Park Reservoir gained 493 ac-ft yesterday and is 52% full, compared with 55% full on average.

Upcoming weather may make fishing the upper river a challenge. Fishing on the lower river should not be as challenging with respect to air temperatures but stronger winds will make dry fly fishing tougher and diminish hatches.

Henry’s Fork, October 29th, 2022

Presenting streamers almost anywhere on the river will be effective. Weedier waters such as in the Harriman State Park reach (and portions of the lower river), will have interrupted presentations from time to time but resident rainbows respond to them even though it is almost traditional to present aquatic and terrestrial insect life cycle patterns. Brown trout are migrating throughout the lower river, and offering streamers during low light conditions is certainly the best way to encounter them.

Henry’s Fork, October 25th, 2022

Headlines from Dr. Rob Van Kirk’s water analysis report taken yesterday for the Henry’s Fork drainage are below

• Wet, cold weather continued yesterday, keeping monthly precipitation at 98% of average.
• Natural flow increased to 89% of average.
• At an outflow of 157 cfs, Island Park Reservoir gained 460 ac-ft yesterday and is 50% full, compared with 52% full on average.
• Water quality: Turbidity dropped at all locations yesterday; high phytoplankton growth continues in Island Park Reservoir.

Flow of only 157 cfs out of Island Park Dam makes wading in Box Canyon quite easy, and presenting streamers very effective. Rubber legs and large nymph patterns also work well. We also have great weather for BWO activity throughout the river. Bundle up and don’t put away that floating line yet!

Henry’s Fork, October 22nd, 2022

Everything we said about the South Fork applies to the lower river. For the upper river, low flow in Box Canyon makes it a good choice for wading. Streamer and nymph patterns, such as rubber legs, should work well there and in the Tubs. Don’t overlook BWOs in these locations as well as at Last Chance and in the Harriman section where wading is also easier. Weather will determine if terrestrial insect patterns will be effective. It looks like our days with 60 to 70 degree F. afternoon air temperatures are gone with snow possible.

Henry’s Fork, October 15th, 2022

It is streamer time in Box Canyon and in the Tubs. Water is low enough in the Box that walk-in-wade fishing beats fishing from a boat because of low water. Another plus is that recreational floater numbers in both places are decreasing as we cool off. Almost anywhere else on the river, terrestrial insect patterns during warm, sunny PMs are best bets to fishing success. Tiny BWOs are out during evenings at certain locations such as just above the Fun Farm Bridge.

Another strategy for this time of day on the lower river is that of using streamers to encounter migrating brown trout.

Henry’s Fork, October 11th, 2022

Sunny, comfortable days make afternoons enjoyable times to be almost anywhere on the river. BWOs, mahogany and midge activity will be somewhat muted because of bright skies, so evenings will offer best times for top water fishing.

Headlines:From Dr. Rob Van Kirk’s Henry’s Fork drainage water status report of yesterday  

• Warm, dry weather continues, with no end in sight.
• Natural flow is 74% of average, and diversion is 110% of average.
• At an average outflow of around 280 cfs, Island Park Reservoir gained 100 ac-ft yesterday and is 46% full, compared with 48% 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