Glossary

In the context of a weather forecast, "actionable" refers to information or predictions that prompt individuals and organizations to take specific measures or make decisions to mitigate potential risks or capitalize on opportunities presented by the forecasted weather conditions. An actionable weather forecast provides clear guidance on what steps should be taken to respond effectively to the expected weather impacts.

California has been a pioneer in setting ambitious renewable energy targets to transition its energy sector to cleaner and more sustainable sources. These targets are part of the state's broader efforts to combat climate change, reduce greenhouse gas emissions, and promote renewable energy generation. Water year precipitation plays a critical role in California's renewable energy landscape, particularly for hydropower generation and water resources. Balancing water availability, hydropower output, and the impacts of changing precipitation patterns is essential for maintaining a sustainable and reliable renewable energy supply in the state.

The Climate Prediction Center (CPC) is a division of the National Weather Service (NWS) under the National Oceanic and Atmospheric Administration (NOAA) that specializes in providing climate forecasts and outlooks. The CPC Seasonal Precipitation Outlooks are forecasts that predict the likelihood of above-normal, near-normal, or below-normal precipitation conditions for specific geographic regions during a particular season.  These outlooks are based on analysis of historical climate data, current oceanic and atmospheric conditions, and global climate models.  They are typically issued on a monthly basis and are valid for a 3-month period.

Hydropower curtailment is the intentional reduction of hydropower due to various reasons but often related to changing water availability. An accurate water year precipitation forecast can be a critical input for estimating water levels in reservoirs which directly affects hydropower generation potential. Knowing the reservoir water availability can allow for optimized generation scheduling.

California is known for its highly variable and often extreme precipitation patterns.  From periods of drought to atmospheric rivers and floods, these extremes have a profound impact. Climate phenomena like El Niño (warmer Pacific Ocean waters) and La Niña (cooler Pacific Ocean waters) can influence California's precipitation patterns.  Overall, precipitation extremes underscore the importance of proactive planning, resilient infrastructure, and sustainable water management practices.

In meteorology, a "forecast domain" refers to the specific geographic area for which a weather forecast is generated.

In meteorology, "lead time" refers to the amount of time in advance that a forecast is provided before a specific weather event is expected to occur. A long-term forecast such as the CAP report gives customers ample time to plan.  This is a critical concept within every industry, as it determines the preparation and response time available for various activities and decisions.

For our purposes, the “normal precipitation” for the state of California refers to the long-term average amount of precipitation (rain, snow, etc) that the state receives within a given water year.  It is important to note that California’s precipitation varies widely due to its diverse geography. The normal annual precipitation value provides a baseline for comparison and helps put current weather patterns into context. It aids in making informed decisions related to water management, agriculture, infrastructure planning, and disaster preparedness.

This phrase refers to the CAP forecast process. CAP is a deterministic forecast; it provides a single, fixed precipitation range for the water year and remains unchanged regardless of how the actual weather conditions evolve. This contrasts with probabilistic forecasts or other forecasts that are regularly updated as new data becomes available (see CPC outlooks). Deterministic forecasts are often considered more actionable than probabilistic forecasts due to their straightforward and specific nature.

Refers to any form of water- liquid or solid- that falls from the atmosphere to the surface.  This includes rain, snow, sleet, hail.  Precipitation is a critical factor in California’s climate, as it affects overall water supply, reservoir levels, agriculture, and overall environmental conditions.

A water year precipitation forecast for California refers to a combined snowfall and rainfall prediction that is anticipated to occur within the specific water year period (October 1st to September 30th), aligning with the state's hydrological patterns and economic needs.  In California, a precipitation forecast of this type is essential for water management, drought and flood preparedness, reservoir planning, agriculture, renewable power generation, and emergency response to name just a few.

This agricultural term refers to a situation where growers are unable to plant crops on all of their intended acreage due to various reasons, including precipitation extremes. Farmers can utilize preventive planting provisions in crop insurance policies to mitigate financial risks associated with unplanted acreage.

A probabilistic forecast is a type of weather prediction that emphasizes the inherent uncertainty in predicting future atmospheric conditions. Unlike deterministic forecasts that provide a single expected outcome, probabilistic forecasts offer a range of possible outcomes along with associated probabilities (percent chance) for each outcome.

While the CAP domain includes most of the state of California, the precipitation forecast can be regionalized further to meet end-user needs. Customization involves dividing the state into smaller, more localized regions to provide tailored precipitation predictions for specific sub-areas.

A statistical model in meteorology is a mathematical framework that uses historical data and statistical techniques to analyze and predict weather-related phenomena. Unlike physical models, which simulate the underlying physics of the atmosphere, statistical models focus on identifying patterns and relationships within observed data to make predictions about future weather conditions.  Statistical models in meteorology are particularly useful when the underlying physical processes are complex and difficult to model accurately, or when data is limited.

Water allocation refers to the distribution of available water resources to various sectors, such as agriculture, urban areas, industry, and the environment. Allocation decisions are made by water managers, agencies, and regulatory bodies to balance the demands. Precipitation forecasts provide crucial information that water managers use to make informed decisions about water resource planning, including effectively and sustainably allocating water resources.

California water managers are individuals, agencies, and organizations responsible for the planning, development, allocation, and conservation of the state's water resources. The California State Water Project (SWP) and the Central Valley Project (CVP) are two significant water management systems in CA.  Managed by state and federal authorities, respectively, these projects are designed to capture, store, and distribute water for various uses.  Given California's diverse climate, geographical features, and water needs, effective water management is crucial to ensure a reliable and sustainable water supply.

In California, a "water year" is a term used to refer to the period of time that begins on October 1st of one calendar year and ends on September 30th of the following year. This timeframe aligns closely with the state's precipitation and hydrological patterns, particularly the rainy season, which typically occurs during the fall and winter months.  “Water year” is especially significant in California due to the state's reliance on precipitation for its water supply, particularly in the form of snowpack in the Sierra Nevada mountains. Snow that accumulates during the colder months serves as a natural reservoir, melting gradually in the spring and summer, releasing water downstream into rivers and reservoirs.  By defining the water year in this manner, hydrologists, water managers, and policymakers can better analyze and predict water availability and plan for water allocation and management. Monitoring snowpack levels, streamflow, reservoir storage, and groundwater recharge within the context of a water year provides a more accurate representation of the state's water resources and helps guide water-related decisions.