Henry’s Fork, October 26th, 2021
As is our usual practice, excerpts from Dr. Rob Van Kirk’s Monday AM analysis of the Henry’s Fork drainage water status are given below.
REPORT NOTE: USBR data sites are down for maintenance this morning, so diversion, streamflow and reservoir data are current only through Saturday. I’ve filled in missing data for USBR weather stations with data from the nearest non-USBR stations.
Headlines:
- Precipitation during the much-anticipated atmospheric river event has so far been highly variable, ranging from a few hundredths in the valleys to over 1 inch in the Centennial Range.
- Diversion and natural flow were around 75% of average until rain increased natural flow in Fall River on Saturday.
- At a mean outflow of 110 cfs, Island Park Reservoir gained 549 ac-ft/day for the week ending Saturday and is 54% full, compared with 52% on average.
Details:
Mean temperature last week was 3 degrees F above average. At 8 degrees F above average, Friday was the warmest day since October 6. Precipitation for the week-—most of which has fallen in the past two days—was highly variable across the watershed, ranging from a few hundredths in the valley locations to 1.3 inches at White Elephant. The Centennial Range and Yellowstone Plateau areas have received by far the highest totals thus far during the much-anticipated atmospheric river event that is bringing heavy precipitation to most areas of the West. Lewis Lake Divide, Black Bear, White Elephant and Crab Creek all received over 0.6 inch of water equivalent last week. Because of warm temperatures, new snow accumulation has been limited to the highest elevations, where Black Bear and Grand Targee have 1.7 inches and 2.5 inches, respectively, of snow water equivalent on the ground–around 80% of average for the date. Precipitation is expected to continue today and tomorrow, with somewhat cooler temperatures arriving this afternoon.
Watershed-total natural flow and diversion stayed around 75% of average until rain on Friday night and Saturday morning increased streamflow in Fall River by 40 cfs or so. Streamflow in the Teton River is also increasing a bit this morning.
We measured outflow from Island Park Reservoir at 114 cfs on Friday. For the week ending Saturday, mean outflow was 110 cfs, and the reservoir gained an average of 549 ac-ft/day. Projecting that gain through the end of yesterday, the reservoir is 54% full, compared with 52% full on average.
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