Summary of CW3E Outlooks During Water Year 2024

April 22, 2024

CW3E summarizes and disseminates key forecast information about potentially hazardous weather over the Western US, with a strong emphasis on landfalling ARs, as part of the California Atmospheric River (AR) and Forecast Informed Reservoir Operations (FIRO) programs. These activities consist of written outlooks, “quick looks”, and post-event summaries of high-impact storms. The outlooks and quick looks provide valuable information and situational awareness guidance to stakeholders, such as the California Department of Water Resources and local water agencies, as well as the general public.

CW3E created and posted a total of 25 outlooks, 27 quick looks/Twitter threads, and 10 event summaries during October 2023 through March 2024. During a particularly active four-week period between 21 January 2024 and 17 February 2024, CW3E posted six outlooks and five quick looks. This period included the record-breaking precipitation and severe flooding event in San Diego County on 22 January 2024 and a strong AR in early February 2024 that produced >10 inches of rain in the Los Angeles metro area. Some locations in Southern California received more than a year’s worth of precipitation in the first 3 weeks of February 2024.

The CW3E outlooks and post-event summaries focus on storm events over the Western US; however, the team also prepared outlooks and event summaries for two exceptionally strong ARs that produced extreme precipitation and widespread flooding over the Eastern US in mid-December 2023 and early January 2024. These activities were sponsored by the nationwide expansion efforts of the FIRO program and funded projects with the NOAA Cooperative Institute for Research to Operations in Hydrology (CIROH).

A more recent initiative supported by the AR Program has involved the creation and posting of subseasonal-to-seasonal (S2S) forecast information via regularly scheduled Subseasonal and Seasonal Outlooks. While the AR outlooks and quick looks focus on weather time scales (forecast lead times of up to 10 days), the Subseasonal and Seasonal Outlooks focus on 2–6 week and 1–3 month lead times, respectively, and are posted between November and March. These longer time scales are a primary concern for the water resource management community, especially given the implications of cool-season precipitation and snowpack for drought and water supply in the Western US. CW3E posted its first S2S outlook in December 2021, and the S2S outlooks team has continuously worked to augment and improve the content in these updates based on an iterative process with direct input provided by practitioners.

In Water Year (WY) 2024, CW3E began posting subseasonal and seasonal forecast information in two unique outlooks; the Subseasonal Outlooks are typically posted weekly, and the Seasonal Outlooks are posted monthly. Both the Subseasonal and Seasonal Outlooks include information from experimental forecast products developed at CW3E and collaborating institutions such as NOAA and the International Research Institute for Climate and Society (IRI), as well as a single prediction based on a synthesis of the products. During WY 2024, CW3E posted 17 Subseasonal Outlooks and 5 Seasonal Outlooks. CW3E will solicit further feedback from users this year and aims to incorporate additional forecast products currently under review into its WY 2025 Subseasonal and Seasonal Outlooks.