FGUS65 KSTR 051825 ESGNM 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: http://www.cbrfc.noaa.gov/product/peakpeak.cgi 2008 Normal 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 Pagosa Springs Animas - 6550 3440 10200 6100 4675 5/28 - 6/14 Durango Animas - 7150 3560 9490 7030 4900 5/31 - 6/15 Farmington San Juan - 11800* 7250 40700 29330 7340 5/21 - 7/4 Bluff * - 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. CBRFC/tjc NNNN $$