Fishing Reports

Henry’s Fork, May 28th, 2022

Those big bugs taht are out are hunkering down. Give them a warm day or two, and their numbers will increase, they will fly, then drop to the water, and the fish will respond maybe way up the river.

Henry’s Fork, May 24th, 2022

It looks like a late year for the giant stone fly event beginning in good numbers. Let’s see what the warming weather of the next few days brings. Looking at what Dr. Rob Van Kirk observes in the Henry’s Fork drainage with respect to effect of cold weather on the drainage, it is no wonder that insect activity is behind for the date. See below

His snow-water analysis for Henry’s Fork drainage of yesterday follows.

Headlines:  

• Another cool, dry day dropped water-year total precipitation to 83% of average but kept snow melt relatively low.
• Natural flow continued to drop yesterday and was 45% of average for the date and 70% of average cumulatively for the water year.
• Diversion held steady at 93% of average.
• At an average outflow of 389 cfs, Island Park Reservoir gained 77 ac-ft and is 99.6% full.

Details:

Mean temperature yesterday was 6 degrees F below average, continuing what has been a very long run of below-average temperatures. Precipitation dropped to 83% of average for the water year so far. Snow melt was a little below average for the date, and 65% of this year’s peak snow water equivalent (SWE) remains yet to be melted, compared with 53% on average. Current SWE at the mid-elevation stations is about average for the date. Cold weather continues to keep aquatic insect hatches delayed by about 5-6 days in the lower watershed. Crop development also continues to lag average due to cooler temperatures.

A couple of warmer days are in store tomorrow and Thursday before cooler weather and precipitation return on Friday and persist through the Memorial Day weekend. Temperatures will be around 5 degrees below average. Precipitation forecasts have not been very consistent, due to a pretty strong gradient between a relatively dry forecast to our southwest and a very wet forecast to our northeast. The latest 7-day quantitative forecast calls for around 0.1 inch along the western edge of the watershed to around 1 inch along the Montana border. Areas just to our northeast, in Yellowstone National Park and southern Montana, could receive up to 2 inches. So, slight changes in moisture feed could mean large differences in actual precipitation amounts. At this point, rain in the valleys would be beneficial, but current forecasts suggest a continuation of the recent pattern of showers in the mountains but little if any in the valleys.

Natural stream flow continued to drop yesterday in response to cooler weather. Natural flow is currently 45% of average for the date and 70% of average for the water year so far. These numbers are truly astounding. In the 1978-2022 record, natural flow for the water year to date in the next driest year to this one (2002) is 79% of average, illustrating just how far this year is away from anything close to “normal.” Diversion stayed constant at 92% of average, dropping the difference between supply and demand down to only 600 cfs above the indicator of need for reservoir draft to meet irrigation demand. With warmer weather on the way—as well as some precipitation—natural flow will meet demand by a small amount at least into next week, although stream flow will be far less than half of average for this time of year throughout the watershed.

At an average outflow of 389 cfs yesterday, Island Park Reservoir gained a very small amount of water and is 99.6% full. Current outflow is just at the right level to keep the reservoir within a few hundred ac-ft of full for the next several days. Outflow may need to be increased a hair at the end of the week to accommodate increased inflow in the form of rain, should forecast amounts creep upward. On a full reservoir, 1 inch of rain adds 625 ac-ft, which is less than the difference between full pool and current reservoir content. Right now, forecasts call for around 0.5 inch in Island Park later in the week.   

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, May 21st, 2022

A few big stone flies reported out, and plenty of boats are on the lower river. Any day now the big bugs will be out in force, and so will those who are now waiting for them whether they be trout or fly fishers.

Henry’s Fork, May 16th, 2022

Giant stone fly nymphs are concentrating along banks and shallows of the lower river, and a few adults may be flying to announce beginning of the main event. Already numerous boats are on the water getting started to enjoy the famed adult stone fly event, and fish responding to ongoing may fly and caddis activity.

Here are a few things of note. The repaving of U.S.Highway 20 between Ashton and the Fall River bridge should be complete in a few days making for no flaggers on one lane sections and the long awaited seven mile smooth ride. Fall River is in run-off mode impacting fishing below Chester Dam. Mosquitos are out in forested areas

Dr.Rob Van Kirk’s Henry’s Fork drainage snow-water report of yesterday is below.

Headlines:  

• Yesterday was the warmest of the spring so far, and forecast showers did not materialize.
• Although cooler weather is forecast for the end of the week, it appears that our 6-week run of above-average precipitation has come to an end.
• Natural flow is increasing rapidly but is only 47% of average for the date at 71% of average for the water year.
• Island Park Reservoir gained over 400 ac-ft yesterday and is expected to fill next week.

Details:

Daily mean and daily maximum temperatures yesterday were both the warmest day since October 5. Showers did not materialize as forecast yesterday, but the Centennial Range received some measurable precipitation. The water-year total dropped a percentage point to 85% of average. Snowmelt was above average due to warm temperatures, and snow water equivalent at the three low-elevation stations is essentially zeroed out for the year. Relative to average, a fair amount of snow remains at the mid- and high-elevation stations in the northeastern corner of the watershed, where precipitation over the past few weeks has been heaviest.

Although cooler temperatures are still expected later in the week, forecasts have trended much drier over the past several days, and it looks like our 6-week run of above-average precipitation has ended. Only light precipitation in the northern-most areas of the watershed is expected over the next week, and long-range forecasts do not indicate any strong precipitation trend one way or the other.

Since April 6, the watershed has received 5.0 inches of precipitation, compared with 4.5 inches on average. Although this does not represent a large exceedance of average, the combination of moderate precipitation and very cold temperatures improved moisture availability in the agricultural regions by 2 inches. However, even with that improvement, one-year accumulated moisture availability is 4 inches below average. Three-year average precipitation improved slightly over the past six weeks but is still over 10% below average.

As anticipated, warm temperatures have increased natural flow watershed-wide but most notably in Fall River. However, natural flow is still exceptionally low—only 47% of average for the date and 71% of the 1978-2021 average for the water year to date. This is the lowest in the 1978-present record by a long shot—the next lowest year is 2002, at 79% of average. In the record of natural flow at Ashton (upper Henry’s Fork subwatershed) that goes back to 1930, accumulated natural flow for the water year to date has dropped to 4^th lowest, behind 1935, 1934, and 1931.

Also as anticipated, diversion continues to increase rapidly and is now 81% of average. Increase in stream flow in Teton River yesterday exceeded increase in diversion there, increasing flow in the Teton River from 25 cfs in each of the North and South forks on Sunday to about 45 cfs in each yesterday. I expect both stream flow and diversion to continue to increase through Friday, but natural flow increase will outweigh increase in diversion during that time. Fall River should reach its second and probably highest peak for the year late this week before cooler weather slows snowmelt again. The Teton River will probably reach a higher peak in two weeks or so. At the system-wide level, the reservoir system has been dropping for nearly a week now and is 58% full. The American Falls storage right has been in priority for only a few short periods over the past two weeks, meaning that paper accrual of storage system-wide has been minimal.

At an average outflow of 212 cfs, Island Park Reservoir gained 414 ac-ft yesterday and is 98% full. Stream inflow increased a little yesterday in response to snowmelt, but evaporation loss reduced net inflow by 26 cfs (6% of stream inflow). The reservoir will continue to gain around 350-400 ac-ft/day, which will put it at full pool early next week.