CW3E Launches New Forecast Tools for the Atmospheric River Scale

November 2, 2020

CW3E has recently launched new tools focused on forecasting the Atmospheric River Scale. The new tools (available here), offer a 7-day forecast and review of the past 7 days for the Atmospheric River (AR) Scale. The AR Scale was originally launched in 2019 (overview video to the right). Similar to the Saffir-Simpson Hurricane Scale, it categorizes atmospheric rivers 1-5. Storms are characterized by the maximum strength, determined by the amount of water vapor they carry, and the winds, and their duration in a given location. Category is assigned based on if the storm will potentially be weak (AR 1), moderate (AR 2), strong (AR 3), extreme (AR 4), or exceptional (AR 5). The scale also indicates if the storm will be beneficial, by relieving drought and refilling water supply, or hazardous, causing flooding and dangerous conditions.

There are two new forecast tools on the page:

1. A forecast of incoming atmospheric rivers and the potential corresponding AR scale ranking at various latitude grid points along the West Coast. Also looks at the past 7 days.

2. A measure of integrated vapor transport (the mix of water vapor and wind that is a signature of atmospheric river storms) at grid points along the West, to give more detail on the magnitude of the storm. Colored shading represents the AR scale observed or forecast for the given time, calculated using the control forecast or ensemble mean.

Interested parties can sign up to get AR Scale alerts via text or email on this page: /arscale_alerts/. Alerts can be customized by locations, frequency, and various thresholds on the AR Scale.

The Center expects the new AR Scale forecast tool to be useful to water agencies that rely on forecasts for reservoir management, as well as broadcast meteorologists. Additional AR forecast tools created by CW3E can be found here: /iwv-and-ivt-forecasts/.

To learn more about atmospheric rivers and the AR Scale, please see the video below: