Science for Cold Air Outbreak Forecasts 3-5 Weeks in Advance:

 

Our forecasts for cold air outbreaks in winter season are based on the relationship of the atmospheric mass circulation 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, our research 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.

 

We calculate 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.

 

Because cold air outbreak events are accompanied with development of low and high pressure system 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.

 

 

Key References

 

• Johnson, D. R., 1989: The forcing and maintenance of global mon- soonal circulations: An isentropic analysis. Adv. Geophys., 31, 43-31.

• Yu, Y-Y, M. Cai, R-C Ren, H. M. van den Dool, 2014: Relationship of Warm Air Mass Transport into Upper Polar Atmosphere and Cold Air Outbreaks in Winter. J. Atmos. Sci., 10.1175/JAS-D-14-0111.1.

• Cai, M., and C-S Shin, 2014: A Total Flow Perspective of Atmospheric Mass and Angular Momentum Circulations: Boreal Winter Mean State. J. Atmos. Sci., DOI:10.1175/JAS-D-13-0175.1.

• Zhang, Q., C-S Shin, H. van den Dool, and M. Cai, 2013: CFSv2 Prediction Skill of Stratospheric Anomalies.   Clim. Dyn. DOI:10.1007/s00382-013-1907-5.

• Ren, R-C and M. Cai, 2008: Meridional and downward propagation of atmospheric circulation anomalies.  Part II: Southern Hemisphere cold season variability. J. Atmos. Sci., 65, 2343-2359.

• Ren, R-C, and M. Cai, 2007: Meridional and vertical out-of-phase relationships of temperature anomalies associated with the NAM variability. Geophys. Res. Lett. , 34, L07704, doi:10.1029/2006GL028729.

• Cai, M., and R-C Ren, 2007: Meridional and downward propagation of atmospheric circulation anomalies.  Part I: Northern Hemisphere cold season variability.  J. Atmos. Sci., 64, 1880-1901.