SLCESGNM May, 2008
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FGUS65 KSTR 051825
TTAA00 KSLR DDHHMM
NATIONAL WEATHER SERVICE
COLORADO BASIN RIVER FORECAST CENTER
SALT LAKE CITY UT
MAY 5, 2008
INTERNAL NWS PRODUCT FOR GUIDANCE PURPOSES ONLY
SAN JUAN RIVER BASIN SPRING FLOOD POTENTIAL OUTLOOK
The potential for spring 2008 flooding due to snowmelt in the San Juan Basin
is higher than average. Most rivers and streams over the upper portions of the
San Juan, Navajo, Piedra, Animas and La Plata are forecast to approach or exceed
bankfull. This is due to much above average snowpack in these areas. Depending
on future precipitation and temperatures, all of these rivers will have to be
monitored closely during runoff over the next several months.
Current snowpack as of May 1st for the entire San Juan Basin is 110 percent
of average. The area above Navajo Reservoir currently has 120 percent of average.
April precipitation was 45 percent of average across the entire Basin,
with seasonal totals since October 2007 at 110 percent of average. The volume
forecast for the April-July runoff period is above average.
It is also important to keep in mind that an extended period of high
temperatures resulting in rapid snowmelt, or heavy rainfall during the peak
flow period when stream channel capacities are reduced, may cause or exacerbate
flood problems this year.
Specific spring peak flow forecasts (maximum mean daily flow) as of May 5th.
Forecast peaks for this year are 50% exceedance values. For full probabilistic
distributions of possible peaks, see:
Fcst 2007 Flood Bankfull Average Period
Peak Peak Flow Flow Peak of
River / Site (cfs) (cfs) (cfs) (cfs) (cfs) Peak
------------------ ------- ------- ------- ------- ------ -----------
San Juan - 3800 1920 6760 4990 2485 5/15 - 6/12
Animas - 6550 3440 10200 6100 4675 5/28 - 6/14
Animas - 7150 3560 9490 7030 4900 5/31 - 6/15
San Juan - 11800* 7250 40700 29330 7340 5/21 - 7/4
* - Peak flow forecast on the San Juan below Navajo Reservoir include
the maximum spring releases for 2008 by a proposed modified Spring Release
(26-days at 5,000 cfs) would be made as determined by the Flow
Recommendations. The modifications would extend the Spring Release by
beginning sooner to by-pass the larger than average inflow and also
running it longer to meet end-of year target storage. The final
decision on the exact nature of this modified Spring Release has not
been determined, but the Bureau of Reclamation's current proposal is to
hold at 2200 cfs until mid May when the maximum Spring Release will begin
to ramp up to 5,000 cfs. The normal 21-day 5000 cfs release will be extended
5 days and then ramp down 1000 cfs each day in late July to the target
baseflow of 750 cfs.