Text Products for ESF Issued by REV

Flood Potential Outlook
Issued by NWS Reno, NV
Versions: 1
000
FGUS75 KREV 051611
ESFREV
CAZ070>073-NVZ001>005-NVZ030>031-NVZ033>041-122300-

Spring Flood Potential Outlook
National Weather Service Reno NV
810 AM PST Tue Mar 5 2024

...Above normal threat of snowmelt flooding along the Humboldt River
and tributaries, and from watersheds draining far northern Nevada,
including the Owyhee, Jarbidge, Bruneau, and Salmon Falls Creek..
Normal threat of flooding from rivers that drain from the eastern
Sierra...

There is an above normal threat of spring snowmelt flooding along
the Humboldt River and its tributaries due to an above normal
snowpack throughout northern Nevada. There is a typical threat of
spring snowmelt flooding for areas along the Carson and Walker
rivers where snowpack conditions have recently climbed to near
normal conditions.

Flooding on rivers can occur from heavy rainfall at any time, or
combined with snowmelt during the spring.

Observations and forecast runoff predictions reported here may
change significantly with additional storms this spring. Please
visit the CNRFC webpage (http://www.cnrfc.noaa.gov) for the latest
information.

Current basin conditions:

Snowpack:

After a dry start to the water year in the Sierra,
numerous storm systems have moved across the region the past two
months, greatly improving the snowpack conditions throughout
California and Nevada. Early March Storms added 4 to 12" of snow
water equivalent (SWE) gains throughout the Sierra, and more modest
gain elsewhere. As of March 4th, the eastern Sierra snowpacks are
near to slightly above normal and well above normal in the remainder
of northern and northeastern Nevada. The Humboldt Basin and other
far northern Nevada basins have already exceeded their median
seasonal peak snowpacks about three to four weeks early. Snowpacks
in the Owyhee, Bruneau, Jarbidge and Salmon Falls Creek all exceed
last year`s snowpack at this time. The early March storm brought
snow to all elevations boosting the low elevation snowpack and
vastly expanding the snow covered area. The eastern Sierra snowpack
is currently 108% of median to date, and 94% of the median seasonal
peak. The snowpack in the Humboldt watershed is currently well above
normal at about 150% of median to date and 120% of median seasonal
peak. Soil moisture is near to slightly above normal in the eastern
Sierra and well above normal throughout the Humboldt and far
northern Nevada. Near normal base flows have been observed from the
east Sierra, and above normal along the Humboldt and northern
Nevada. Accumulated volume on the lower Humboldt at Imlay is nearly
double the to-date median.

Precipitation:

Precipitation totals across northern Nevada are now near normal in
the Sierra and above normal in northern Nevada. Precipitation
outlooks from the Climate Prediction Center currently show near
normal precipitation across California and Nevada during the 1 to 2
week timeframe. No clear signals for above or below normal
precipitation exist for the week 3-4 timeframe and into April-May.
Temperatures are projected to lean above normal this spring but
confidence is mixed.

Seasonal (April - July) runoff forecasts:

The seasonal April-July runoff forecasts are above average
throughout the Humboldt watershed. Forecasts range from near 135% to
170% of average along the mainstem of the Humboldt River. In the
Carson and Walker basins, seasonal forecasts are near normal at
around 80-100% of average. These seasonal  forecasts may change
significantly with spring storms, or lack thereof. Please check
cnrfc.noaa.gov for updates.

Flood exceedance probabilities:

The risk of flooding during the spring is elevated in the Humboldt
basin due to the above normal snowpack and elevated baseflow. With a
shallow, low elevation snowpack in place across the northern
Humboldt watershed, the flooding potential is further elevated due
to the potential for a late season rain-on-snow event or an early
heat wave. Models currently show a near 75% chance of minor flooding
on the Marys River and along the Humboldt River at Comus. There is
also an elevated flood risk for the Owyhee, Bruneau, Jarbidge, and
Salmon Falls Creek in far northern Nevada. There is a slight risk of
flooding on the Carson and Walker rivers, as the snowpack in these
watersheds is now near normal with significant low elevation snow.
The flood risk is low for the Truckee, Susan and Middle Fork of the
Feather from snowmelt alone. These drainages and others are all
susceptible to flood risk in the event of a warm and strong late
season atmospheric river event.  Consult the AHPS long-range flood
risk map for the latest point exceedance probabilities for the March
through May time period:
https://water.weather.gov/ahps/region_long_range.php?rfc=cnrfc

Summary:

The risk of flooding during the spring is elevated along the
Humboldt River and its tributaries, as well as the Owyhee, Jarbidge,
Bruneau, and Salmon Falls Creek, due to the above normal snowpack,
low elevation snow, and above average baseflow and soil moisture.
The flood threat is near normal along the Carson and Walker rivers,
where the current snowpack is near average. Flooding can occur from
snowmelt, rain, or a combination of both. Refer to the long range
outlook product for updates to flood exceedance probabilities at
specific locations throughout the spring. For short term hydrologic
forecasts and general water resource information, please see the
CNRFC webpage at: http://www.cnrfc.noaa.gov

For more detailed water supply and streamflow forecast information
for Nevada and eastern California, please refer to the following web
sites,

NWS California-Nevada River Forecast Center...
http://www.cnrfc.noaa.gov/water_supply.ph

NWS Reno for weather updates along with watches and warnings for
hazardous weather and flooding conditions...
http://weather.gov/reno

Nevada Natural Resources Conservation Service...
http://www.nv.nrcs.usda.gov/snow/

California Department of Water Resources...
http://cdec.water.ca.gov/

NWS Climate Prediction Center Long Range Outlook Maps...
http://www.cpc.ncep.noaa.gov/products/forecasts/

U.S. Drought Portal...Including U.S. Drought Monitor...
http://drought.gov/

TB/MI
National Weather Service Weather Forecast Office
