Author: Bruce_Staples

Henry’s Fork, March 7th, 2023

Headlines from Dr. Rob Van Kirk’s March 6th Henry’s Fork drainage SWE report

• Precipitation was light yesterday but still over-performed in the Ashton area.
• Heavy precipitation is expected Friday and possibly early next week.
• Current SWE is 108% of average for the date and 90% of the average annual peak.
• At an outflow of 233 cfs, Island Park Reservoir gained 218 ac-ft yesterday and is 83% full, compared with 79% 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, February 7th, 2023

Here is an important detail from Dr. Rob Van Kirk’s snow-water equivalent (SWE) report compiled yesterday for the Henry’s Fork watershed.

I will emphasize that average snow pack this winter—if we actually even achieve that—will not bring average stream flow. Stream base flows this winter are still in the range of 70-80% of average, and the springtime snow melt will be superimposed on that very low base—not on top of average stream flow. Average SWE this will winter will bring us natural stream flow in the range of 80-90% of average, which is much better than last year but still well below 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, January 31st, 2023

Headlines from Dr. Rob Van Kirk’s Snow-Water Equivalent Report Compiled Yesterday

• Yesterday’s watershed-averaged minimum and mean temperatures ended up just a fraction of a degree warmer than those on December 22, but most stations in the watershed set new low-temperature records for the date.
• Water-year total precipitation is 104% of average, and SWE is at 106% of average.
• If SWE stays at 106% of average the rest of the winter, expected April-September streamflow will be 90-95% of average.
• At an outflow of 266 cfs, Island Park Reservoir gained 104 ac-ft yesterday and is 77% 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

Henry’s Fork, January 17th, 2023

Headlines From Dr. Rob Van Kirk’s SWE Report of Yesterday for the Henry’s Fork Drainage.

• Thanks to a solid storm over the weekend, precipitation last week was above average, keeping the water-year total at 110% of average and increasing SWE to 115% of average.
• Generally dry conditions with below-average temperatures are expected for the next two weeks. New snow water equivalent (SWE) was 19% above average for the 8-day period, ranging from 1.4 inches at Phillips Bench (Teton Pass) and Grassy Lake to 3.0 inches at Grand Targhee. Current SWE is 115% of average: 104% in Teton River, 107% in Fall River, and 129% in upper Henry’s Fork. Upper-level atmospheric flow has shifted from southwest to northwest, finally putting an end to three weeks of continuous heavy precipitation in California. For us, the change means cooler-than-average temperatures and generally dry conditions for the next week or two. If that forecast proves to be correct, water-year precipitation here will drop relative to average over the next week to around 107% of average, and SWE will drop to 105% of average.
• At an outflow of 201 cfs, Island Park Reservoir is 75% full, compared with 73% full on average.
• Combined volume in the three reservoirs in the watershed caught up to average yesterday, at 79% full.

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, January 10th, 2023

Headlines From Dr. Rob Van Kirk’s SWE report of yesterday for the Henry’s Fork drainage.

• Yesterday was warm and wet, keeping water-year precipitation at 110% of average but increasing SWE a notch to 115% of average.
• Moderate precipitation is expected to continue on and off for the foreseeable future.
• Natural stream flow in the upper Henry’s Fork sub-watershed continues to hover in the range of 75-77% of average.
• At an average outflow of 203 cfs, Island Park Reservoir gained 390 ac-ft yesterday thanks to good precipitation and is 73% full, compared with 72% 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, 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