Fishing Reports

Henry’s Fork, February 8th, 2022

During nicer days midge activity is dense enough to provide some good top water fishing up and down the river, but getting to the river can be a problem in many places.

Dr. Rob Van Kirk’s report for today, February 8th, on snow and water conditions in the upper Henry’s Fork drainage are given below.

Headlines:  

• Water-year precipitation stayed at 96% of average yesterday, but SWE dropped to 80% of average.
• Island Park Reservoir gained 187 ac-ft yesterday, a little higher than it was 7-10 days ago but well below the rates of 250-350 ac-ft/day we saw during periods of heavy precipitation in December.
• Natural flow in the upper Henry’s Fork sub-watershed remains around 75% of average.
• Dry weather will continue until at least next Monday.

Details:

Mean temperature yesterday was 2 degrees F below average. No precipitation was recorded, leaving the water-year total at 96% of average. Snow water equivalent (SWE) dropped to 80% of average. Forecasts are hinting at precipitation next Monday, but we’ve seen such forecasts fall apart week after week over the past month.

Most stream gages in the watershed remain affected by ice, but the Island Park and Ashton gages on the Henry’s Fork show that natural flow in the upper Henry’s Fork watershed is around 75% of average, where it has been since late last summer.

Island Park Reservoir gained 187 ac-ft yesterday, higher than what we saw 7-10 days ago but nowhere near the rates of 250-350 ac-ft/day observed back in December during periods of precipitation. Since December 1, outflow has average 218 cfs, and fill has averaged 247 ac-ft/day. The reservoir is 81% full, compared with 75% 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, January 11th, 2022

Excerpts From Dr. Rob Van Kirk’s Henry’s Fork drainage water report for today are below.

Headlines:  

• Dry conditions have set in for around 10 days, during which water-year precipitation and SWE will fall with respect to average and reservoir fill rates will drop.
• Water-year precipitation is 116% of average, and SWE is 104% of average this morning.
• At a mean outflow of 218 cfs, Island Park Reservoir gained 227 ac-ft yesterday, compared with 265 ac-ft/day needed over the remainder of the winter to reach the April-1 target.

Details:

Mean temperature yesterday was 5 degrees F below average. Water-year precipitation dropped to 116% of average and SWE to 104% of average. Dry conditions are expected to last into the beginning of next week, by which time SWE will be 5-7% below average again.

At a mean outflow of 218 cfs, Island Park Reservoir gained 227 ac-ft yesterday and is 77% full, compared with 72% full on average. Since December 1, the reservoir has filled at 295 ac-ft/day, ahead of the 265 ac-ft/day needed over the remainder of the winter to reach the April-1 target 126,000 ac-ft (93% full). If precipitation in Island Park stays above-average for the rest of the winter, as is expected, the reservoir will reach the April-1 target at an average outflow of 216 cfs, within measurement error of current outflow. If reservoir fill rates deviate too much one way or the other from forecasts, outflow adjustments will need to be made later in the winter to keep the reservoir on track to meet the target.

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]

HFF blog

Henry’s Fork, January 8th, 2022

Dr. Rob Van Kirk’s Henry’s Fork drainage snow water equivalent (SWE) report of January 7th is below. It’s data suggests that we are off to a good start in accumulating snowfall in the drainage.

DATA NOTE: The Grassy Lake and Black Bear SnoTel stations have been reporting incomplete data for the past few days. I have estimated these using available data, but I anticipate adjustments once complete data are reported again. Those adjustments may affect precipitation totals and temperatures.

 Headlines:  

• Precipitation yesterday was the heaviest since December 23, increasing the water year total up to 119% of average and SWE up to 111% of average.
• Reservoir fill rates increased again yesterday due to the heavy precipitation, especially at Henry’s Lake and Grassy Lake.
• At an outflow of 222 cfs, Island Park Reservoir gained 309 ac-ft yesterday, compared with 261 ac-ft/day needed over the remainder of the winter to reach the April-1 target.
• Warm, wet weather is expected to continue today before a lengthy dry spell sets in.

Details:

Yesterday was the warmest and wettest day since December 23. Temperature was 7 degrees above average, and precipitation averaged 0.54 inch across the watershed. The Teton and Fall River subwatersheds were favored. Water-year precipitation is now 19% above average for the watershed and above average at all 12 stations. New snow water equivalent (SWE) accumulations ranged from 0.2 inches at Crab Creek to 2.3 inches at Grand Targhee. This increased the watershed-total SWE to 11% above average. SWE is above average at all SnoTel stations except Grand Targhee, which is at 98% of average.

Warm, windy, and wet conditions are expected today before an extended dry period sets in. Temperatures in inversion-prone valley areas will be average to below average, while elevations above inversions will see above-average temperatures next week.

In response to precipitation and warmer temperatures, total gain in the watershed’s three reservoirs increased from 220 ac-ft on Monday to 482 ac-ft yesterday. The increases were most notable at Grassy Lake and Henry’s Lake. Grassy Lake gained only 11 ac-ft on Monday but 33 ac-ft yesterday and is 67% full, compared with 76% full on average. Henry’s Lake actually lost some volume last weekend but gained 140 ac-ft yesterday. Henry’s Lake is 88% full, compared with 89% full on average.

At an outflow of 222 cfs, Island Park Reservoir gained 309 ac-ft yesterday. Average fill rate since December 1 is 307 ac-ft/day, compared with 261 ac-ft/day needed the rest of the winter to meet the April-1 target. The reservoir is 77% full, compared with 71% full on average. Together, the three reservoirs in the Henry’s Fork watershed are 81% full, compared with 78% on average. The upper Snake River reservoir system as a whole is 36% full, compared with 56% 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, December 14th, 2021

Anywhere you try the Henry’s Fork open to fishing, winter conditions will be your companion. Happy Holidays!

Excerpts from Dr. Rob Van Kirk’s Henry’s Fork watershed report released yesterday follow.

Headlines:  

• Yesterday was warm again but the wettest since November 19, moving water-year precipitation up to 94% of average.
• New SWE accumulation was heavy yesterday, especially in the upper Henry’s Fork, increasing watershed-averaged SWE to 68% of average.
• Natural flow increased to 83% of average in response to warmer temperatures and low-elevation rain.
• Island Park Reservoir gained 625 ac-ft yesterday, over half of which was due to direct precipitation, and is 71% full, compared with 67% full on average.

Details:

Mean temperature yesterday was 9 degrees above average, and moderate to heavy precipitation fell across the watershed. Low elevations received a mix of rain and wet snow, while all SnoTel stations accumulated new snow water equivalent (SWE). Precipitation totals ranged from 0.02 inch at Alta to 1.3 inches at White Elephant. As has been the case recently, the upper Henry’s Fork and Fall River subwatersheds received the most precipitation. The watershed average was 0.43 inches, the highest one-day total since November 19. Water-year total precipitation increased from 91% of average yesterday to 94% of average this morning. New SWE totals ranged from 0.2 inch at Pine Creek Pass to 1.3 inches at White Elephant and averaged 0.7 inch over the nine SnoTel stations. This improved SWE from 62% of average yesterday to 68% of average today. Temperatures will drop back to average tonight and stay near to slightly below average for the next week or two. Above-average precipitation is expected to continue for the foreseeable future.

Watershed-total natural streamflow increased in response to yesterday’s warm temperatures and low-elevation rain. Natural flow was 17% below average yesterday. Cumulative natural flow for the water year to date is still 23% below average.

USGS measured outflow from Island Park Reservoir at 213 cfs yesterday afternoon. Updated outflow data are around 7% lower than I have been reporting for the past month or so. The reservoir gained 625 ac-ft yesterday, over half of which was from direct precipitation on the reservoir surface. Since December 1, reservoir outflow has averaged 205 cfs, and the reservoir has gained 325 ac-ft/day. An average fill rate of 270 ac-ft/day is needed to reach the April-1 reservoir target of 93% full. The reservoir is currently 71% full, compared with 67% 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

[email protected]

HFF blog