National Weather Service Raw Text Product

122 
AGUS74 KWCO 221326
AHDNWC

Area Hydrological Discussion #311 - EXPERIMENTAL
NWS National Water Center - Tuscaloosa, AL
712 AM CST Fri Nov 22 2024

WHAT: Small stream, river, and flash flooding
WHERE: Northern California
WHEN: Through this evening

FORECAST RAINFALL AND ANTECEDENT CONDITIONS...
QPF: 2 - 4"+ (HRRR)
Rainfall Rates: 0.25 - 1"/hr (WPC)
QPE: Widespread 2 - 7", locally higher (48 hr MRMS QPE)
Soils: Saturated (80%+ 10 - 40 cm RSM, NASA SPoRT)
Streamflows: Above normal (USGS)

DISCUSSION...
Rainfall will continue across the area of concern through this
evening as the atmospheric river affecting the region persists. Based
on antecedent conditions, any additional rainfall is expected to
quickly and efficiently lead to runoff. Soils are nearly completely
saturated and streamflows are all running higher that the 95th
percentile for historical flows. This will likely produce associated
pluvial and fluvial hydrologic responses, which should also increase
in number and magnitude as time progresses. Additionally, rockslides
and landslides will become increasingly possible as soils become
completely saturated and thus unstable.

The National Water Model (NWM) Short Range Forecast (SRF) continues
to highlight potential for rapid onset flooding (ROF) between Eureka
and San Francisco and along western slopes of the northern Sierra
Nevada between Redding and Chico. Probabilities for ROF are generally
between 25-50%. Corresponding flows also within these areas are
mostly near 50% with localized probabilities less than 10% AEP,
suggesting confidence in small stream flooding.

GRAPHICAL REPRESENTATION weather.gov/owp/operations-ahd

Additional National Water Center products are available at
weather.gov/owp/operations

//TMK

ATTN...WFO...MFR...REV...MTR...EKA...STO
ATTN...RFC...RSA...WPC