The California State Climatologist collects and interprets climate data for California, and disseminates climate data and information through various means, including this website. The California State Climatologist is a function of the 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)
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 section.
The California Hydroclimate Report
Recent observed extremes in temperature and precipitation have raised awareness of the potential influence of a changing climate on meteorological and hydrological outcomes. As a complement to the advance planning work on adapting to and mitigating climate change impacts, the Hydroclimate Report looks to document the events of each water year and provide context of those events to the current climate state and expectations for change. The report series begins with water year 2015, when a new record low for April 1 snowpack was observed, and continues through water year 2018. The report for the previous water year is expected to be available around the beginning of the new calendar year. Older editions of the report are being formatted to meet ADA accessibility standards and will be linked to this page when they are complete.
- 2021 Hydroclimate Report (PDF, 6 MB)
- 2020 Hydroclimate Report (PDF, 18 MB)
- 2019 Hydroclimate Report (PDF, 24 MB)
- 2018 Hydroclimate Report (PDF, 24 MB)
- 2017 Hydroclimate Report (PDF, 23 MB)
- 2016 Hydroclimate Report (PDF, 8 MB)
- 2015 Hydroclimate Report (PDF, 21 MB)
Climate Summaries from 2006-2018
Each month the State Climatologist compiles a brief summary of weather conditions, snowpack, and water supply conditions, as well as graphics showing statewide temperature and precipitation rankings for the month. These summaries have been compiled into single Adobe Acrobat files for previous calendar years, while monthly summaries for the current year will be posted separately. These files are available by sending a request to Flood@water.ca.gov.
The California State Meteorologist prepares weather summaries for forecasting and flood operations and coordinates DWR's meteorological activities with the National Weather Service and other relevant government agencies and interested parties. Other activities include:
- Advising on developments in meteorology and climatology and representing California's interests in the meteorological aspects of water resources;
- Coordinating data collection on wind, temperature, radiation, humidity and evaporation;
- Advising engineers on meteorological conditions affecting design of hydraulic structures; and
- Planning and coordinating meteorological studies for refining forecasting techniques regarding water supply and floods, especially at key geographical locations that concern DWR.