The last bits of remnant ice on Dillon Reservoir near the Dillon Amphitheater on May 21. Bob Berwyn photo.
Late winter delays melt-off a bit past the average date
By Bob Berwyn
FRISCO — It took a little longer than normal, but Denver Water’s water managers said Dillon Reservoir finally became fully ice-free on Friday, May 24, exactly the same date as two years ago, in 2011, after one of the snowiest winters on record. Prior to that, you have to go all the way back to 1995 to find a later date (May 30).
Dillon-based reservoir-keepers have been tracking the dates the reservoir freezes over and thaws out completely since 1965 as part of their regular duties. The so-called ice-off date generally falls in the middle of May. In fact, the ice has only lasted into June once — after the monster winter of 1983, when it didn’t thaw until June 7.
The earliest ever full-thaw date was last year, when all the ice was gone by April 18 following all-time record March warmth. 2012 was one of only two years on record when the ice melted in April. The other April melt-off was in 2002, following another severe drought winter.
The earliest Dillon Reservoir has frozen over completely was Dec. 1, 1990, nearly three weeks ahead of the average date, which generally falls right around Christmas. This winter’s freeze-over date was Dec. 26, following two years 2010 and 2011) with unusually late ice-on dates. In both those years, the reservoir froze solid on Jan. 1.
The latest the reservoir has ever frozen over was Jan. 30, 1980, during another infamous warm and dry winter.
Currently, the water level in Dillon Reservoir is rising at the rate of several inches per day, with the Blue and Snake rivers, Tenmile Creek and the smaller tributaries all hovering around peak seasonal flows. As of May 21, the reservoir elevation was 8,989.11 feet, holding about 180,000 acre feet (capacity is 257,304 acre feet). That’s still about 27 feet below full (9,017 feet).
Full list of ice-on & ice-off dates (courtesy Denver Water)
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