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 33rd 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
P.O. Box 550
Ashton, ID 83420
208-652-3567 OFFICE
208-881-3407 CELL
208-652-3568 FAX