A team of researchers led by Scripps Institution of Oceanography at the University of California San Diego has created a scale to characterize the strength and impacts of “atmospheric rivers” mainly for the mid-latitudes. This Polar AR scale utilize an adapted version of the original AR Scale with additional IVT thresholds based on a climatological study of IVT over the Antarctic region to account for lower water vapor transport. Three additional AR rankings (AR A1, AR A2, and AR A3) have been added to the scale. The Antarctic AR scale is determined based on the duration of AR conditions (IVT >100 kg m-1 s-1) and maximum IVT during the AR, the same methodology as described in Ralph et al. 2019, but with lower thresholds added. This Polar AR scale was widely tested during the YOPP-SH Winter Targeted Observing Periods and has been proven to be able to quantify the impacts of ARs accurately based on their strength and duration, which benefits both forecast operations and research.

Real-time forecast products are host at Center for Western Weather and Water Extremes (CW3E) website: https://cw3e.ucsd.edu/arscale/

This polar AR scale is developed at CW3E with help from Dr. F. Martin Ralph, Dr. Jason Cordeira, Dr. Zhenhai Zhang, Brian Kawzenuk.