When it comes to precipitation forecasting, understanding both the amount and timing is crucial. 

The California Annual Precipitation (CAP) forecast by Weather Tools was developed to answer the question so many Californians are asking – “Will it be a wet or dry year?” 

CAP is the only forecast that has accurately predicted the total water year precipitation for seven consecutive years.  

But can CAP tell you when it will rain?

The CAP forecast is designed to provide an overview of the expected total water year precipitation for California, expressed in 20% ranges relative to normal. 

For instance, it might forecast that the state will receive 20-40% above normal precipitation for a given water year. 

However, CAP does not directly forecast precipitation timing.  Despite this limitation, CAP can still offer timing insights as the water year progresses. 

By tracking the cumulative precipitation and comparing it to the CAP forecast, we can make inferences about what lies ahead.

For example, during the 2022-23 water year, CAP forecasted that California would receive 20-40% above normal precipitation. 

Yet, in the January update, the state had only reached 42% of water year total. 

Seeing this significant gap between the current and forecasted numbers, we alerted subscribers that a wet spring was in store, potentially coinciding with rice planting and almond bloom. 

Indeed, significant rains followed, and by the close of the water year (September 30) the water year total was 43.3% above normal.

While CAP gives subscribers a high-level view, our portfolio includes additional products for more granular forecasting. 

The daily forecast product, leveraging a network of 47 automated weather stations, provides hourly updates and a 10-day forecast of key atmospheric variables. 

This daily forecast includes additional value-added metrics and gives actionable insights based on current and short-term weather data.

These daily forecasts use machine-learning techniques to enhance accuracy, even in areas with sparse data. 

For precise timing information, CAP can be complemented with Weather Tools daily forecasts. 

This combination ensures that Californians are well-equipped to manage their water resources effectively throughout the year.

If you’re interested in learning more about how our CAP or daily forecast can serve your needs, send an email (rob@weathertools.org) or give me a call (530-774-5475)!