New Forecasts Made on February 4：
In this week’s forecast, we are forecasting a new STRAT PULSE event, named as STRAT_M, to take place during the period 03/03-03/08 with its peak around 03/04. The STRAT_M event will lead to cold air surges over both North America and Eurasia during the forecasted time period.
Minor stratospheric sudden warming event has taken place after STRAT_J as we forecasted:
The first stratospheric polar vortex breakup event, first forecasted on 12/30, has taken place after a mega PULSE event, STRAT_J. As indicated in Figure below, the STRAT_J already peaked on 01/26. Because of the massive warm air mass transported into the polar stratosphere during STRAT_J, the westerly jet surrounding the Arctic decreased substantially, reaching a minimum velocity of 17 m/s at 5 hPa on 01/31 from 67 m/s just a week ago. This corresponds a minor stratospheric sudden warming event. In short, our forecasts for this polar vortex breakup event were successful in terms of both timing and intensity.
Follow up on Forecasts Made in Previous Weeks:
STRAT_K (02/02-02/07), first forecasted on December 31, has been materialized, which makes it a 30+ day forecast. As we forecasted, the first peak of STRAT_K was recorded on 02/02 and the second peak is going to take place on 02/06. Both peaks have a moderate peak intensity of 0.6 trillion tons warm air mass transported into the polar stratosphere per day. Despite of the moderate intensity, it is driven by stronger wave activities of wave number 1, which is more favorable for cold air outbreaks to take place over North America. It will cause 60% area of North America with below-normal temperature and only mild cold air surges over limited areas of the Eurasia. According to GFS week-1 forecasts for the surface air temperature, the cold temperature will first occur over the western regions of North America and then spread over the entire continent.
STRAT_K1 (02/12-02/15), first forecasted on January 22, is expected to occur within our forecasted time window with its peak around 02/12. Mainly driven by stronger wave activities of wave number 2, STRAT_K1 will cause below-normal temperatures over a large area of both continents. The GFS week-2 forecasts suggest that from 02/12 to 02/17, there will be large-amplitude cold temperature anomalies over both continents.
STRAT_L (02/19-02/26), first forecasted on January 22, is expected to occur on time. This event seems to be extra long-lasting event with multiple peaks. The first peak could occur as early as 02/18 and the second peak is on 02/25, as we forecasted last week. The first peak is more associated with wavenumber 1 and the second peak with both wavenumber 1 and 2. Therefore, based on the statistical relationship between PULSE events and spatial patterns of cold air outbreaks, we expect a substantial increase in the cold area first appearing over North America, and then expanding to both continents due to multiple back-to-back cold air outbreaks associated with this extra long-lasting PULSE events with multiple peaks.