March storms came up a little below average and the snowpack started to melt, then stopped and built back up a few tenths of SWE. The end result was the forecast drifting lower and somewhat flattening at the end of the month.
The 50% Most Probable (MP) Forecast based on April 1 snowpack came in at 250 KAF, while the 70% Forecast came in at 220 KAF. The MP at 250 KAF provides a small managed release (spill) for about a week. The 70% spill will not produce a boating release if it comes down in atypical pattern. We will not plan to start this release until the reservoir elevation is between 6920 and 6922. Today McPhee is at elevation 6895 and we do not expect to reach release levels until late in May. The runoff is just starting and will rise and fall with temperatures. Upper Dolores flows usually hit their peak near May 20, a likely time for us to reach near full if the runoff comes off normally. Temperatures, new storms or dust on snow can all affect the runoff timing.
So a small spill still remains possible. It will not be definite until later in May and will be short, 5 – 10 days max, with about one week’s notice before it starts. We will operate as a “fill in spill”, and start releases when we approach full at 6924, available on Lake Elevation tab. Runoff timing, early vs. late, along with future weather will drive the specific size and timing of any excess water spilled downstream. We will update again in several weeks close to May 1 as new information, such as precipitation, becomes available.