New Forecasts Made on January 27：
No new forecasts are made in this week’s forecast.
Minor stratospheric sudden warming event is going to happen after STRAT_J:
On 12/04, we forecasted a break-up event of stratospheric polar vortex to occur after STRAT_H. It turned out that STRAT_H indeed forced the polar stratosphere lopsided with the center relocated off the North Pole. The westerly wind surrounding the polar vortex weakened greatly (say Fig. 1 below). The polar vortex did manage to regain its strength due to lack of strong stratospheric pulse events before STRAT_J.
On 12/30, we made a forecast saying that the first stratospheric polar vortex breakup event may take place after STRAT_J because of the anticipated 1.0+ trillion-tons-per-day intensity of STRAT_J. STRAT_J just peaked two days ago, within the time period we first forecasted on 12/23 and the peak intensity of STRAT_J was as strong as 1.4 trillion tons per day. As indicated in Fig. 1 below, the mega event, STRAT_J, already led to a much weaker westerly jet surrounding the Arctic with the average zonal wind speed in the region 50-80°N around 30m/s, a nearly 40m/s weakening from that just a week ago. In the coming 3 days, STRAT_J is expected to continue transporting anomalously more warm air into polar stratosphere, causing a further weakening of the polar vortex. Therefore, we are confident about our original forecast for a minor stratospheric sudden warming event right after STRAT_J.
Follow up on Forecasts Made in Previous Weeks:
STRAT_K (02/02-02/07), first forecasted on December 31, is expected to take place on time with its peaks achieved on 02/02 an 02/06. As we forecasted, STRAT_K is a moderate PULSE event. It maybe responsible more than 60% area of North America back to below-normal temperature indicated by up to 30% increase of cold area, although it will result in only mild cold air surges over Eurasia.
STRAT_K1 (02/12-02/15), first forecasted on January 22, is expected to occur within our forecasted time window with its peak around 02/14. Mainly attributed to stronger wave activities of wave number 2, STRAT_K1 will cause below normal temperatures over both continents.
We are continuing to forecast the STRAT_L (02/19-02/26), first forecasted on January 22, to be a strong and week-long event with its peak around 02/24. As we forecasted last week, the peak of STRAT_L is mainly due to stronger wave activities of both wave number 1 and 2, thus will result in several rounds of cold air surges within the week after 02/22 over mid-latitude regions of both continents, particularly North America.