Sub-seasonal Forecasts of Winter Storms and Cold Air Outbreaks
"Our technology is a dynamics-statistics hybrid model to forecast continental-scale cold air outbreaks 20-50 days in advance beyond the 2-week limit of predictability for weather."
Professor Cai's team has developed a technology that allows them to make Sub-seasonal forecasts for cold air outbreaks in winter season. These forecasts are made on the basis of the relationship of the atmospheric mass circulation intensity and cold air outbreaks. The atmospheric poleward mass circulation aloft into the polar region, including the stratospheric component, is coupled with the equatorward mass circulation out of the polar region in the lower troposphere. The strengthening of the later is responsible for cold air outbreaks in mid-latitudes.
Due to the inherent predictability limit of 1-2 weeks for numerical weather forecasts, operational numerical weather forecast models no longer have useful forecast skill for weather forecasts beyond a lead time of about 10 days. Recently, the research carried out by Professor Cai and his team shows that operational numerical weather forecast models do possess useful skill for atmospheric anomalies over the polar stratosphere in cold seasons owing the models' ability to capture the poleward mass circulation into the polar stratosphere.
They calculate the stratospheric mass transport into the polar region from forecast outputs of the US NOAA NCEP's operational CFSv2 model and use it as our forecasts for the strength of the atmospheric mass circulation. The anomalous strengthening of it is indicative of the high probability of occurrence of cold air outbreaks in mid-latitudes.They further derive a set of forecasted indices describing a state of stratospheric mass circulation to obtain detailed spatial pattern and intensity of the associated cold air outbreak events.
Because cold air outbreak events are accompanied with development of low and high pressure systems and frontal circulations, our forecasts of cold air outbreaks are also indicative of snow, frozen rain, high wind, icy/freezing and other winter storm related hazards besides a large area of below-normal cold temperatures.