Author: Bruce_Staples

Henry’s Fork, April 12th, 2022

We are in a period of “BWO” weather. If you can stand the accompanying wind and precipitation, afternoon top water fly fishing can be worth a visit along the lower river. . Dress warmly and wade carefully! Banks are clearing making access an improving situation. Presenting streamer and stone fly nymph patterns will also bring action during this period of relatively good overhead cover.

Excerpts from Dr. Rob Van Kirk Henry’s Fork drainage SWE report of this morning are below. It contains some long awaited good news.

Headlines:  

• Yesterday was the wettest since January 6, increasing water-year precipitation to 80% of average and SWE to 67% of average.
• Natural flow dropped yesterday in response to cold temperatures.
• Due in part to direct precipitation, Island Park Reservoir gained 444 ac-ft yesterday and is 93% full, compared with 86% on average.
• Cold, unsettled weather is expected to continue for the rest of the week.

Details:

As mentioned yesterday, we could have used our current weather back in February. Mean temperature yesterday was 9 degrees F below average and roughly equal to average at the end of February. Precipitation overachieved for a change and was the highest one-day total since January 6, the last day of the only extended wet period we had all winter. Precipitation totals ranged from 0.11 inch at Rexburg to 0.8 inch at White Elephant and averaged 0.38 inch over the watershed. This was enough to move the water-year total from 78% of average to 80% of average.

Cold temperatures put a temporary end to snowmelt, and all SnoTel stations except Island Park gained snow water equivalent (SWE) yesterday. New SWE ranged from 0.3 inch at Crab Creek to 1.3 inches at Phillips Bench and averaged 0.6 inch over the watershed. This moved SWE up two percentage points to 67% of average. It also moved SWE back ahead of 2001 and 2015, the two years with lowest SWE in the 1989-2022 record. SWE on the ground this morning is the highest for the season so far at all high-elevation stations and most of the mid-elevation stations. Date of peak SWE for the whole watershed is still March 22, but tomorrow’s SWE will most likely be the new peak for the season. Average peak date is April 12.

Very cold and unsettled weather will continue for another few days. Although temperatures will warm, precipitation remains in the forecast off and on into the beginning of next week. The 7-day quantitative forecast calls for 0.25 inch along the western edge of the watershed, 0.5-0.75 inch in the Island Park area and up to 1.75 inches along the Wyoming border. That will be enough to keep the water-year total up above 80% of average and is likely to push SWE up to 70% of average. Snowmelt will remain minimal at least through Friday.

After a small, short-duration bump, natural streamflow dropped yesterday in response to cold temperatures over the past two days. Natural flow is 71% of average: 76% in upper Henry’s Fork, 68% in Fall River, and 62% in Teton River. I expect natural flow to stay pretty constant for the next few days.

Due in part to direct precipitation on the reservoir surface, Island Park Reservoir gained 444 ac-ft yesterday to each 93% full, compared with 86% full on average. Outflow will likely be increased again to prevent reservoir ice from encroaching on spillway infrastructure as the reservoir continues to fill.  

Henry’s Fork, March 15th, 2022

Excerpts from Dr. Rob Van Kirk’s Henry’s Fork drainage water report of this morning are below.

 Headlines:  

• Water-year precipitation stayed at 83% of average yesterday, while SWE dropped to 69% of average.
• Stream gages are starting to come back on line after a very long period of ice, showing natural flow in the range of 75-80% of average.
• Temperatures and precipitation are expected to stay near climatic averages for the next week.

Details:

Mean temperature yesterday was 2 degrees F below average, extending a streak of nine consecutive days of temperatures at or below average. With snowpack as low as it is, cold weather is critical to keeping that snow on the ground as far into the spring as possible. After a dry day, snow water equivalent (SWE) dropped back to 69% of average yesterday, while water-year precipitation stayed at 83% of average.

Current SWE is still ahead of that for the date in 2001 and 2010. Subsequent spring and summer weather differed substantially between those two years, resulting in two very different outcomes for the water year as a whole. April-September precipitation in 2001 was 21% below average, while that in 2010 was 19% above average. That difference resulted in 2001 ending up with the lowest natural streamflow in the 1978-2021 record, at 73% of average, compared with 75% of average in 2016 and 76% of average last year. By contrast, natural flow in 2010 ended up at 87% of average, ranking above the 33^rd percentile of water years since 1978. So, a wide range of outcomes is still possible, although anything close to average water supply is not one of them.

Light precipitation is expected this afternoon through tomorrow and again on Saturday night and Sunday. Total precipitation amounts over the next week are expected to range from around 0.1 inch along the western edge of the watershed to around 1 inch along the Wyoming border. If those totals are realized, precipitation this week will be about the same as it was last week and close to average for mid-March. Temperatures are expected to stay near average. After that, above-average temperatures are in the forecast beginning next Tuesday, although long-range outlooks do not show any strong indication that either temperature or precipitation will deviate much from average.

Stream gages are starting to come back on line after a very long period during which ice has prevented real-time flow observations. The St. Anthony gage on the Henry’s Fork and Ashton gage on Fall River are the first two to return to real-time transmission. Based on data available as of yesterday, natural streamflow is in the range of 75-80% of average in both the upper Henry’s Fork and Fall River.

Island Park Reservoir gained 232 ac-ft yesterday and is 87% full, compared with 80% full on average. Reservoir content will reach 120,000-123,000 ac-ft by April 1.

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, March 12, 2022

Nicer but unsettled weather is predicted for the coming week. With increasing BWO activity on the lower river, some decent top water fishing should take place but river still has limited approaches. Streamer and stonefly nymph patterns remain effective when presented in deeper runs and holes where you can get to them..

Excerpts from Dr. Rob Van Kirk’s Henry’s Fork drainage Snow Water Equivalent (SWE) report of yesterday, March 11th, are below. The data give a grim picture of current SWE in the area.

Headlines:  

• More low temperature records were set yesterday, which started out with the coldest minimum in over five years.
• Water-year precipitation dropped to 82% of average, while SWE stayed at 68% of average.
• Reservoir fill rates were even lower yesterday than on Wednesday. Island Park is 86% full, compared with 79% full on average.
• After today, temperature and precipitation are expected to be near climatic normal for the next week or two.

Details:

Yesterday morning was the coldest in the watershed since December 17, 2016. In the 12-station 1989-2021 record I use for the whole watershed, yesterday’s minimum, mean, and maximum temperatures all set new records for the date. The low of -16.5 degrees F broke the old record of -3.2 degrees set in 2006. The daily maximum of 17.0 degrees broke the old record of 21.1 degrees, set in 2009. The daily mean was a whopping 27 degrees below average for the date and the second coldest day of the winter, behind January 1. That beat the old March-10 record by 9 degrees. Even at stations with very long periods of record, yesterday’s low temperature broke records for the date by wide margins. Idaho Falls set a new record low of -7 degrees, breaking the old record of 4 degrees, set in 1969.  

No precipitation was recorded yesterday, dropping the water-year total to 82% of average. Snow water equivalent (SWE) stayed at 68% of average. After another day of below-average temperatures, forecasts and long-range outlooks all call for temperature and precipitation near climatological averages. In the short term, light precipitation is expected on Sunday, with slightly heavier precipitation on Tuesday and Wednesday. The latest 7-day precipitation forecast looks a little better than it did yesterday, with 0.25-0.5 inch expected over most of the lower elevations of the watershed and up to 1.25 inches along the Teton crest. If realized (big if), that would be roughly average for this time of year.

As you might imagine, stream gages throughout the watershed remain affected by ice. The Island Park and Ashton gages are the only two that have provided reliable data all winter, and both show natural flow in the upper Henry’s Fork at around 75% of average.

Reservoir fill rates were even lower yesterday than they were on Wednesday. Island Park Reservoir is 86% full, compared with 79% on average, and the three reservoirs in the watershed are 87% full, compared with 84% full on average. The upper Snake River reservoir system is 50% full, compared with 74% 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

Henry’s Fork, March 8th, 2022

Access to the lower river from the Ora bridge downstream to Chester is opening up. Increasing BWO activity during afternoons and midge hatches are providing some top water fishing that will increase as we move through this month. Life cycle patterns of these insects will produce. Streamer and giant stone fly nymphs will attract post-spawning rainbows almost anywhere in the river.

Fun Farm Bridge at Dusk

Excerpts from Dr. Rob Van Kirk’s Henry’s Fork drainage water status report of this morning follow.

Headlines:  

• Light snow late yesterday kept water-year precipitation at 82% of average and SWE at 67% of average.
• Island Park Reservoir continues to fill slowly but steadily at a rate of around 200-210 ac-ft/day.
• Light to moderate snow is forecast watershed-wide today.

Details:

Mean temperature yesterday was 12 degrees F below average and will stay that cold for the next several days. Snowfall arrived yesterday evening as forecast, but only a few hundredths of an inch were recorded through midnight, mostly in the valleys. Widespread snow is expected today, accompanied by strong winds and very cold temperatures this afternoon and evening. Unfortunately, water-equivalent totals now look to be lower than anticipated yesterday, a consistent pattern over the past two months. The heaviest snowfall appears to be headed to our south again, as happened a few days ago. More precipitation is expected Sunday and into next week, but this far out, forecast precipitation could easily disappear.

At an average outflow of 214 cfs, Island Park Reservoir gained 201 ac-ft yesterday and is 85% full, compared with 79% full on average. Yesterday I reported that the mean winter (December-February) outflow from Island Park Reservoir was 218 cfs, compared with 360 cfs on average. Winter flow in the Buffalo River was 200 cfs, compared with an average of 214 cfs, so total flow through Box Canyon—the most important variable determining survival of juvenile trout—was 418 cfs, 73% of average. However, natural stream flow was much lower than average this winter regardless of the effect of storage in Island Park and Henry’s Lake. In absence of the two reservoirs, stream flow through Box Canyon this winter would have been only 516 cfs. Thus, the actual stream flow through Box Canyon this winter was 81% of the river’s natural flow, not a bad outcome following last year’s very dry irrigation season.

:

Senior Scientist

Rob Van Kirk, Ph.D.

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