Warm and Dry Conditions Favored to Continue: La Niña Likely Through Spring
- 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.
- Forecasts favor continued above normal temperatures, dry patterns especially the southern part of the region, and continued drought degradation.
- Drought impacts are growing and preparation for a potential dry year (and second dry year for some areas) is needed.
U.S. Drought Monitor Conditions: California-Nevada |
U.S. Drought Monitor for CA/NV for December 8, 2020. Source: https://droughtmonitor.unl.edu/.
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.
- Extremely dry fall has degraded and expanded drought conditions. Current ridging off the California coast has directed moisture north towards Alaska.
- Evaporative demand has been extremely high and soil moisture is low throughout the region.
- Water Storage (reservoir+snow) in Lake Tahoe region is above normal and near normal in the Sierras but declining.
- There is potential for the development of snow drought conditions due to warm temperatures and/or low precipitation.
Percent of Normal Precipitation for the Last Year. Source: HPRCC
3-Month Evaporative Demand Drought Index (EDDI) from NOAA/ESRL and the Great Basin Dashboard.
Soil Moisture Percentiles from the UCLA Drought Monitor.
Drought Impacts
- The California Department of Water Resources announced the initial water allocation of 10% for the State Water Project.
- Condition monitoring reports since the start of the water year note impacts such as reduced pasture and animal and plant stress, and reports recall conditions similar to 2014/2015.
- Wildfire threats have continued into December due to record warmth and dry fuels.
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) with a potential transition to neutral conditions in April - June (~50%). For more information, check out the NOAA ENSO blog. Although La Niña events historically have resulted in drier conditions in southern CA and NV, this is not always the case. The figure below illustrates the precipitation anomaly for the different climate divisions during the most recent 4 La Nina years.
Seasonal Drought Outlook
As of the mid-November seasonal (3-month) drought outlook, drought was expected to persist for most of the region and develop in the central and southern coast of California. Drought has developed in much that region with no improvements yet in northernmost California-Nevada as forecasted. The next season drought outlook will be released later this month.
Temperature & Precipitation
Current forecasts show dry conditions for the next two weeks in southern California and Nevada and potential moisture to the north early next week. However, seasonal forecasts continue to show the dipole of wet/cool and dry/warm conditions along the west coast as common with La Niña conditions. Seasonal forecasts from NOAA NWS Climate Prediction Center will be updated later this month.
December 16-20th 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 forecast precipitation from from Dec 10-16 from NOAA NWS California-Nevada River Forecast Center.
Drought Early Warning Resources
Observations & Monitoring
- U.S. Drought Portal: Snow Drought Current Conditions Update (launching Dec 17th)
- 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 Impact 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
- National Drought Mitigation Center Drought Planning
- California Drought Planning Resources
- Nevada Drought Planning Resources
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
This Drought Status Update is issued in partnership between the National Oceanic and Atmospheric Administration (NOAA) and the California-Nevada Climate 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.
