California State Climatologist
California State Climatologist
What is CoCoRaHs?
CoCoRaHS (Community Collaborative Rain, Hail and Snow Network) is a grassroots volunteer network of backyard weather observers of all ages and backgrounds working together to measure and map precipitation (rain, hail, and snow) in their local communities. For more information on this program, please visit the National CoCoRaHS website or the State of California CoCoRaHS website. To become a CoCoRaHS observer, use the online application.
Climate Change Symposium From May 23 to May 26 in Palm Springs, CA
From May 23 to May 26, the American Society of Civil Engineers Environmental Water Resources Institute is hosting a climate change symposium in Palm Springs, CA. More information on the event can be found at: http://content.asce.org/conferences/ewri2011/.
New Product for Evapotranspiration Forecasting
The National Weather Service Sacramento Weather Forecast Office in partnership with the University of California and Department of Water Resources has launched a new experimental forecast product for evapotranspiration. For more information on this product, please visit National Weather Service Sacramento Weather Forecast Office. We are seeking comments and feedback on the new product. Please send any feedback about the ETo forecast to the Sacramento NWS Webmaster.
The California State Climatologist collects and interprets climate data for California, and disseminates climate data and information through various means including this portal. The California State Climatologist is a function of the California Department of Water Resources' Division of Flood Management and is a member of the American Association of State Climatologists.
Climate vs. Weather (What to expect vs. What is happening)
April Climate Notables
- Maximum: 13.0 inches in WY1948
- Minimum: 0.43 inches WY1939
- Average: 3.9 inches
- Maximum: 13.13 inches in WY1967
- Minimum: 0.20 inches WY2008
- Average: 3.5 inches
- Eureka 56.4
- Redding 71.3
- San Francisco 63.9
- Sacramento 71.1
- Los Angeles 71.0
- Fresno 74.5
- San Diego 67.4
- Death Valley 89.8
Climate is the expected state of weather variables such as precipitation or temperature. Climate values are defined as averages of weather variables over time periods such as 30 years. For example, the monthly mean temperature for December is a climate variable. This value is computed using observed temperatures in December over a time period of 30 years. Weather is the state of the atmosphere at a given moment in time. An example would be the air temperature on January 1, 2006. Over time, the individual weather values are incorporated into the climate values as they are averaged into the long-term value. A climate forecast provides information on how close the coming monthly values are expected to compare to the long term values for large spatial areas. A weather forecast is much more specific in that it provides information on temperature, precipitation, wind, etc. for the next several days at given locations. For weather summaries and forecasts, please visit the California State Meteorologist site.
Regional Climate Data
Each hydrologic region in California on the map below leads to tables of regional climate normals based on the 1971-2000 period as well as climate normals for selected sites in that region. For the selected sites, the tables may include mean monthly maximum, minimum and average temperatures, monthly average precipitation, and average HDD and CDD values. Temperatures are in degrees Fahrenheit and precipitation is in inches. HDD and CDD values are explained below.
Heating Degree Day units - Monthly sum of the difference between the base temperature and the daily average temperature computed for each day. One HDD unit is accumulated for each degree Fahrenheit the average temperature is below the base temperature. Negative numbers are not included. Example: If the day's average temperature were 47, the base 50 HDD value for the day is 50 - 47 = 3. This is done for each day of the month and the monthly sum is the HDD value.
Cooling Degree Day units - Monthly sum of the difference between the daily average temperature and the base temperature. One CDD unit is accumulated for each degree Fahrenheit the average temperature is above the base temperature. Negative numbers are not included. Example: If the day's average temperature were 75, the base 60 CDD value for the day is 75 - 60 = 15. This computation is done for each day of the month and the monthly sum is the CDD value.
Also, climatologic averages, trends, and extremes for California can be found by following the Climate Data link. Check out the Related Links page for additional sources of climate data and information.