Extended Streamflow Guidance
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FGUS65 KSTR 072127
ESGNM
TTAA00 KSLR DDHHMM
NATIONAL WEATHER SERVICE
COLORADO BASIN RIVER FORECAST CENTER
SALT LAKE CITY UT
May 7, 2019

 SAN JUAN RIVER BASIN SPRING FLOOD POTENTIAL OUTLOOK


Peak flows due to snowmelt are expected to be above average
this spring. Highest peaks in the San Juan Basin are more
frequently associated with summer monsoon rain events than with
snowmelt. The latest hydrologic model guidance does not indicate
flood levels being reached even at the 10% exceedance probability
level.

Streamflow peaks are expected to run in the top 25-30 percent of
the historical record throughout the San Juan Basin. Areas that
have experienced high water issues during heavy snowpack years will
be at risk again this year.

The primary flood threat may be if heavy rainfall occurs during
the peak runoff period when channel capacities are reduced. Additionally
recent rain and low elevation snowmelt has all but eliminated soil
moisture deficits in those areas that existed when the runoff season began.
Any additional heavy rainfall is likely to run off with greater
efficiency than it would have over the past few weeks.

As of early April snowpack conditions in the San Juan Basin are 145
percent of normal above Navajo Reservoir and 180 percent of average
in the Animas River Basin.

Seasonl runoff volumes (April-July) are expected to range from near
110 to 140 percent of average.

Given the large snowpack this year the spring runoff peak flow outlook
will continue to evolve with a and possibly change over couple of weeks
depending on the snowmelt pattern and future weather.

The most recent snowmelt peaks can be accessed on the CBRFC website
at:

https://www.cbrfc.noaa.gov/lmap/lmap.php?interface=peak

G. Smith/ CBRFC

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