Drought Status Update and Resources for California-Nevada | December 22, 2020

Some rain and snow last week and some ahead though drought conditions remain.

Key Points

Building on dry conditions in the last year, drought has expanded and worsened in California and Nevada since the start of the water year due to below average precipitation and above normal temperatures and evaporative demand.
D4 (Exceptional Drought according to the U.S. Drought Monitor) is now present in California as well as Nevada.
Last week the northern parts of California and Nevada received between 0.5 to 2 inches of rain throughout much of the region.
7-day precipitation forecasts indicate between a trace and 3 inches of precipitation for Central and Northern California and far Northwest Nevada.
Even with the recent and forecast precipitation, drought impacts remain and preparation for a potential dry year (and second dry year for some areas) is needed.

U.S. Drought Monitor Conditions: California-Nevada |

December 15, 2020

Regions affected by Moderate (D1) to Exceptional (D4) Drought:

95%

of California is experiencing Moderate to Exceptional Drought (D1-D4)

21%

of California is experiencing Extreme Drought (D3)

of California is experiencing Exceptional Drought (D4)

99.7%

of Nevada is experiencing Moderate to Exceptional Drought (D1-D4)

24%

of Nevada is experiencing Exceptional Drought (D4)

Population affected by drought:

30.5 Million

people in California are in drought

2.7 Million

people in Nevada are in drought

U.S. Drought monitor map of California and Nevada, as of December 15, 2020. Shows drought conditions throughout most of California and Nevada, including Exceptional Drought (D4) in eastern Nevada.

U.S. Drought Monitor for CA/NV for December 15, 2020. Source: https://droughtmonitor.unl.edu/.

95%

of California is in Moderate to Exceptional Drought (D1-D4)

99.7%

of Nevada is in Moderate to Exceptional Drought (D1-D4)

20%-30%

odds of reaching normal precipitation for Water Year 2021

Current Conditions

The dry start to the 2021 water year (Oct. 1, 2020 - Sept. 30, 2021) continues to build California and Nevada precipitation deficits from last year with new development in Southern California.
According to the U.S. Drought Monitor, areas of Severe Drought (D2) to Exceptional Drought (D4) expanded in S. California where precipitation during the past 90-day period has generally been less than 25% of normal. These areas largely have missed recent storm events that have impacted central and northern portions of the state.
In S. Nevada, areas of Exceptional Drought (D4) expanded in Clark County. McCarran International Airport (through Dec. 1) has had 240 days without measurable precipitation ending on 16th Dec, a station record observed for the period.
Evaporative demand over the last month has been high and soil moisture and shallow groundwater is low throughout the region.
Water Storage (reservoir+snow) in Lake Tahoe region is above normal because of high lake levels after recent wet years and below normal in the Sierras due to low snowpack. Dry snow drought conditions due to low precipitation are present across the Sierras and the Southwestern U.S.
The odds of reaching normal precipitation for the water year is between 20% to 30% throughout much of California and Nevada.

Map of California and Nevada Showing Percent of Normal Precipitation for the Last Year. Most regions show lower precipitation than normal, including regions with values of 5% or lower in southeast California and Nevada — Percent of Normal Precipitation for the Last Year. Source: HPRCC

1-Month Evaporative Demand Drought Index (EDDI) from NOAA/ESRL and the Great Basin Dashboard. Valid December 17, 2020, and shows ED4 drought conditions in southeastern California and Nevada. — 1-Month Evaporative Demand Drought Index (EDDI) from NOAA/ESRL and the Great Basin Dashboard. Valid December 17, 2020.

California-Nevada Map Showing Soil Moisture Intensity from the UCLA Drought Monitor. Valid December 19, 2020. — Soil Moisture Percentiles from the UCLA Drought Monitor. Valid December 19, 2020.

NASA GRACE-based shallow groundwater drought indicator map for the contiguous U.S. Shows dry conditions across the western U.S., including California and Nevada. Valid December 14, 2020. — NASA GRACE-based shallow groundwater drought indicator. Valid December 14, 2020. Source: https://nasagrace.unl.edu/

Graph showing water storage in 28 Western Sierra reservoirs plus snowpack. Water storage compared to 1981-2010 was below normal through December 15, 2020.

Graph showing water stored in Lake Tahoe (above rim) plus snowpack. Water storage compared to 1981-2010 is near normal through December 16, 2020. — Water Storage compared to 1981-2010 was below normal in the Western Sierra through December 15 (top) and near normal in Lake Tahoe through December 16 (bottom). Source: CNAP Water Storage Tracking

Map of the western U.S. showing the odds of Water Year 2021 reaching 100% of water year normal precipitation. The odds of reaching normal precipitation is between 20-30% throughout the region. — The odds of reaching normal precipitation based on historical water year totals. The dry start to the water year means the odds of reaching normal precipitation is between 20-30% throughout the region. Learn more about the product at CW3E website.

Drought Impacts

The impact of both short- and long-term dryness in parts of California has been affecting the cattle ranching industry with numerous drought impact reports describing severe impacts to pasture and rangeland conditions as well as reports of ranchers having to sell livestock.
The California Department of Water Resources announced the initial water allocation of 10% for the State Water Project (December 1st).

Report Your Drought Impacts

Drought & Climate Outlook

ENSO

NOAA’s ENSO alert system status is currently a La Niña advisory and is likely to continue through the Northern Hemisphere winter 2020-21 (~95% chance during January-March). For more information please check out the NOAA ENSO blog.

Western Regional Climate Center recently developed a handout about the La Niña impacts for the West. Check it out to see how La Niña historically has affected your region.

Seasonal Drought Outlook

As of the mid-December seasonal (3-month) drought outlook, drought is expected to persist for most of the region and develop in the far southern coast of California.

Temperature & Precipitation

Current forecasts show potential moisture in N. and central California later this week, with a possibility of precipitation in S. California early next week. The 8-14 forecast (below) shows drier than normal conditions for most of the region. Newly released NOAA NWS Climate Prediction Center seasonal forecasts continue to show the dipole of wet/cool and dry/warm conditions along the west coast as common with La Niña conditions.

December 29 - January 4 temperature outlook for the United States. Shows probability of below-normal temperatures for Nevada and southern California. — December 29-January 4 Precipitation Outlook (top) and Temperature Outlook (bottom). A = chances of above-normal; EC = equal chances of above, below, normal; B = chances of below-normal. Source: NOAA NWS Climate Prediction Center. How do I interpret these graphics?

6-day precipitation forecast from from December 22-28 from the National Weather Service's California-Nevada River Forecast Center. — 6-day forecast precipitation from from December 22-28 from NOAA NWS California-Nevada River Forecast Center.

Drought Early Warning Resources

Observations & Monitoring

U.S. Drought Portal: Snow Drought Current Conditions Update (launched December 17)
U.S. Drought Monitor
California State Climatologist, California Data Exchange Center,
Nevada State Climatologist
National Drought Mitigation Center: Condition Monitoring Observer Reports (CMOR) and Drought Impacts Reporter
Western Regional Climate Center (Past ENSO strength/precipitation figures)
WestWide Drought Tracker
Community Collaborative Rain, Hail, and Snow Network (CoCoRaHS)
California-Nevada Applications Program Resources: Water Storage Tracking, UCLA Drought Monitor, Precipitation Tracking
Climate Engine
Great Basin Dashboard
U.S. Water Watcher

Predictions & Forecasting

Weather Forecasts: Your Local National Weather Service office, NOAA NWS California-Nevada River Forecast Center (streamflows)
Subseasonal-to-seasonal (two weeks to three months): NOAA NWS Climate Prediction Center, ENSO, ENSO Blog
1-month Evaporative Demand Drought Index (EDDI) Forecasts
Experimental Forecasts from the Center for Western Weather and Water Extremes Precipitation Forecasts, including:

Planning & Preparedness

Prepared By

Amanda Sheffield
NOAA/NIDIS California-Nevada DEWS Regional Drought Information Coordinator
Email: amanda.sheffield@noaa.gov

Julie Kalansky
Program Manager, California-Nevada Applications Program (NOAA RISA team)
Email: jkalansky@ucsd.edu

Special Thanks

This Drought Status Update is issued in partnership between the National Oceanic and Atmospheric Administration (NOAA) and the California-Nevada Applications Program, a NOAA RISA team, to communicate the current state of drought conditions in California-Nevada based on recent conditions and the upcoming forecast. NIDIS and its partners will issue future Drought Updates as conditions evolve.

The next California-Nevada Drought & Climate Outlook webinar will take place on Monday, January 25 at 11 am PT.