Atmospheric River Scale Forecast Alerts

The AR scale was designed to be applied to Atmospheric Rivers during the winter months. Due to this CW3E will be suspended AR Scale alerts during the summer starting May 1. Alerts will begin again starting October 1, 2024. You may still subscribe to alerts at any time, any additions during the summer months will take effect on October 1.

The AR scale is determined based on the duration of AR conditions (IVT >250 kg m-1 s-1) and maximum IVT during the AR as described in Ralph et al. 2019.

Below you can sign up to receive email or text alerts when ARs are forecasted to impact the U.S. West Coast in the next seven days based on the AR Scale using the Global Ensemble Forecast System (GEFS) or the European Centre for Medium-Range Weather Forecasts Ensemble Prediction System (ECMWF EPS) control forecast. You may choose to receive alerts approximately every six hours (with each new model initialization; GEFS only), twice a day (00 and 12 UTC (4 PM and 4 AM PDT) model initializations), or once a day (00 or 12 UTC (4 PM or 4 AM PDT) model initializations) if an AR is forecasted to impact the region chosen below. Note alerts will be sent ~5-6 hours after model initialization time. Alerts from the ECMWF EPS are only available for the 00 and 12 UTC initialization times .To sign up for these alerts provide you name, email address and/or phone number and mobile provider (phone number only required if text messages are chosen) that would like to receive the alerts at, your affiliation, and the model(s), region(s), thresholds, and frequency you would like to receive alerts for. Model options are the control members from either the NCEP Global Ensemble Forecast System (GEFS) or the European Centre for Medium-Range Weather Forecasts Ensemble Prediction System (ECMWF EPS). Threshold options for receiving alerts are to be alerted of all ARs (AR Scale 1-5) or just strong ARs (AR Scale 3-5). Options for regions to receive alerts are the full U.S. West Coast (Washington, Oregon, and California), the Pacific Northwest (Washington and Oregon), British Columbia, California, Washington, Oregon, Northern California (42oN – 38oN), Central California (38oN – 35oN), or Southern California (35oN – 32.5oN) (see map on right). Note that some regions encompass smaller regions, if a larger region is chosen it is not necessary to also select the smaller regions for the same AR Scale threshold. You will receive a separate email for each region/threshold that is chosen below.

Due to SMS message restrictions text message alerts will provide less information than full email alerts and thus will only contain the maximum forecasted AR Scale for the region chosen.

Email alerts will contain the maximum forecasted AR Scale for the region chosen and the coastal maximum AR Scale and precipitation forecast graphic will be attached. Each email will also contain a link to the AR Scale forecast webpage.

To sign up for alerts provide the requested information, select the alerts you would like, and click submit. You may submit up to five different alert types with each submission, to submit less than five simply leave the rows that you do not want blank, to submit more than five alert types you may do multiple submissions.

AR Scale Alerts 2

To unsubscribe or change your alerts please contact

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