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SPRING FLOOD POTENTIAL OUTLOOK NATIONAL WEATHER SERVICE CALIFORNIA-
NEVADA RIVER FORECAST CENTER SACRAMENTO CA
1000 AM PST FRI FEB 28 2025

A low threat of snowmelt flooding exists across Nevada along the
Humboldt River and its tributaries. A low threat of snowmelt
flooding is present along rivers that drain into Nevada from the
eastern Sierra

There is a low threat of spring snowmelt flooding along the Humboldt
River and its tributaries. The high elevation snowpack is near to
above normal for this date. There is a low threat of spring snowmelt
flooding in the eastern Sierra along the Truckee, Carson, and Walker
rivers where snowpack conditions are currently below normal.
Flooding can occur from snowmelt, rain, or a combination of both at
any time during the winter and spring months.

Current basin conditions

Snowpack

The high elevation snowpack is near to above normal across
much of the Humboldt River basin, with most snow pillows reporting
between 100-130% of median. The snowpack at lower elevations is
nonexistent in most areas, as much of what little was in place
melted off during a warm stretch of weather the last week of
February. The snowpack throughout the Carson and Walker river basins
is below normal, with most stations reporting between 75-95% of
median. The snowpack is a bit heavier across the Truckee basin,
which is close to normal for many areas. Low elevation snow across
the eastern Sierra is modest, as several recent storm events brought
rain at relatively high elevations, which helped to melt low
elevation snow. In addition, some of the low elevation snow has
melted off as a result of warm temperatures the last week of
February.

Precipitation

Precipitation totals across northern Nevada have been
slightly below normal in most areas, with the Ruby Mountains being
slightly above normal. Precipitation across the Carson and Walker
basins has been below normal this year, with year-to-date totals
running about 10-30% below normal. Across the Truckee basin,
precipitation totals are running a bit higher, with most areas just
below normal. Soil moisture is currently tracking slightly below
normal across the Sierra basins, in addition to the upper Humboldt.
Soil moisture is slightly above normal across the lower Humboldt as
a result of recent rain events.

Seasonal (April  July) runoff forecasts

The seasonal April-July runoff forecasts are near median for many of
the tributaries in the upper Humboldt watershed. Forecasts range
from near 90% to 110% of median for most locations. In the Sierra
basins, seasonal forecasts are near median, ranging from about 90-
115% of median in the Carson and Walker basins. Forecasts are 100-
125% of median across the Truckee basin. The snowpack, particularly
at higher elevations, typically does not peak until around the first
week of April. As a result, these seasonal forecasts can change
significantly as a result of additional storms or dry, warm weather
during the month of March.

Flood exceedence probabilities

The risk of flooding during the spring is low with models currently
showing less than a 10% chance of minor flooding on the upper and
lower Humboldt River. There is a low risk of flooding for the east
Sierra, as the snowpack in these watersheds is currently below
normal. Consult the NWPS long-range flood risk map for the latest
point exceedance probabilities for the March through May time
period: https://water.noaa.gov/long_range

Summary

The risk of flooding during the spring is low along the
Humboldt River and its tributaries and in the eastern Sierra.
Flooding can occur from snowmelt, rain, or a combination of both at
any time during the winter and spring months. For a wide range of
short- and long-range hydrologic forecast products, and general
water resource information, please visit the CNRFC webpage at:
http://www.cnrfc.noaa.gov

CNRFC/MI