RECENT ACTIVITIES AT NOAA’S CALIFORNIA NEVADA RIVER FORECAST CENTER

Alan Haynes, Hydrologist in Charge, NOAA/NWS/CNRFC

New Forecast Locations & Recalibrations

The California Nevada River Forecast Center (CNRFC) added several new forecast points on the Central California Coast and one in Southern California:

• Uvas Reservoir

• Upper Penitencia Creek

• Chesboro Reservoir

• Lake Elsman

• Coyote Creek near Highway 237

• New River at Westmoreland

The CNRFC performs re-calibrations yearly on its watersheds on a rotating basis. Recalibrations performed in the summer of 2022 focused on watersheds on the Northern California Coast, the Klamath basin and the Santa Ana basin.

Expansion of Forecast Locations for the Hydrologic Ensemble Forecast Service (HEFS)

The CNRFC added 44 new HEFS locations in the following geographic areas:

• Central Coast including the Salinas

• Lower San Joaquin to Vernalis

• Lower Feather including Yuba City and Nicolaus

• Whitewater River in the Coachella Valley

HEFS Documentation

The CNRFC enhanced its documentation on interpreting HEFS graphics: https://www.cnrfc.noaa.gov/documentation/ hefsShortRangePeakCapabilities.php

Links were also added to additional HEFS information:

• informational videos produced by COMET/ MetED and available on YouTube

• a detailed document describing the implementation of HEFS at the CNRFC

• general theory for ensemble streamflow forecasts

• instructions on creating “build your own” HEFS graphics

• a review of current limitations of HEFS

These links are available on the CNRFC HEFS page: https://www.cnrfc.noaa.gov/hefs.php

Updated Multi-Year Accumulation Plots

The CNRFC makes multi-year accumulation plots that account for the past two years of accumulated runoff volume plus the probabilistic forecast volume for the current water year. These plots illustrate any cumulative deficits/excesses over the past two years with the current year forecast added to the mix. An example graphic is shown below for inflow to Lake Oroville:

This graphic shows that the three-year cumulative runoff volume ending September 30th, 2023 into Lake Oroville (Full Natural Flow) is likely to fall well above the record low three-year volume of 7670 kaf but below the mean volume of 16400 kaf.

New Hydrologic Forecaster Selection

The CNRFC selected Michael Hittle for a hydrologic forecaster position. Mike previously worked at the Sacramento District of the US Army Corps of Engineers as a hydrologist and previous to that he worked for Kings Canyon NP and a variety of other outdoor environmentally-focused positions. Mike has a BS degree in Environmental Physical Science from Black Hills State University and an MS degree in Environmental Science with an emphasis in Hydrology and Water Security from the University of Oklahoma Online Campus.

CW3E Meteorologist Embedded in CNRFC/DWR Operations

The CA Dept. of Water Resources (DWR) has contracted Chad Hecht, a meteorologist from the Center for Western Weather and Water Extremes (CW3E) to be embedded in joint NWS/DWR river forecast operations at the Joint Operations Center (JOC). The goal of this embedded position is to facilitate Research to Operations (R2O) and Operations to Research between river forecast operations and the research community at CW3E.

Cooperative Institute for Research to Operations in Hydrology (CIROH)

The National Oceanic and Atmospheric Administration (NOAA) has a relatively new cooperative institute to facilitate research to operations in hydrology called CIROH. The NWS river forecast community is partnering with the institute to tackle science and research and development issues associated with hydrologic prediction. A call went out for proposals in the fall of 2022 and these proposals are currently being evaluated and approved proposals will be announced and granted funding in early 2023.

Series of Atmospheric River Storms Strike California

A series of about five Atmospheric River (AR) weather systems hit California starting just after Christmas in 2022 and persisting until mid-January. ARs are winter storms that tap into significant, but narrowlyfocused tropical moisture and dump copious amounts of precipitation where they land. Over a threeweek period, these storms dropped 15-20 inches of precipitation over much of the coastal mountains from Northern CA into the Santa Ynez range near Santa Barbara and also over the Sierra Nevada, where much of it fell as snow in the higher elevations. As of late January, the statewide snow water content averaged nearly 220% of average to date, or about 125% of the April 1st average. The northern part of California’s Central Valley received in excess of ten inches of rain while the southern part of the Central Valley received about 3-6 inches. The coastal plain from Los Angeles to San Diego received 6-8 inches, while the mountains picked up 10-15 inches. The excessive rainfall caused flooding on Coastal River Systems from near Arcata to San Diego and brought the Salinas River above flood stage for the first time since 1995. Flooding was also extensive in the Central Valley of California, mainly for the smaller creeks and streams. Water levels were high in the Sacramento and San Joaquin rivers, but mostly stayed below flood stage except for some minor exceedances on the Upper Sacramento. The largest reservoirs in Northern CA mainly did not need to engage flood releases due to years of draw-down, but they did gain significant storage. For example, both Lake Shasta and Lake Oroville gained about a million acre-feet of storage and built up the snowpack in the upper watersheds. Heavy rains brought Folsom Lake above the flood pool prompting large reservoir releases up to 35,000 cfs. Lake Cachuma near Santa Barbara rose about 40 feet in less than two days at one point in January, and gained about 130,000 acre-ft since the first of the year. The CNRFC meteorologists will publish a storm summary this summer for this series of storms on the CNRFC website