New Forecasts Made on February 11：
No new PULSE event is forecasted in this week.
Major stratospheric sudden warming event took place after STRAT_K:
The first stratospheric polar vortex breakup event, which was minor and was first forecasted on 12/30 by us, took place after the mega PULSE event, STRAT_J. After that, the polar vortex was significantly weakened but the westerly jet was not reversed. There was another PULSE event, STRAT_K, took place soon after STRAT_J (first peak on 02/04 and the second peak on 02/08), as we first forecasted on 12/31/2015 to occur within the time window from 02/02 to 02/7. The STRAT_K, though not a large amplitude PULSE event, delivered the final punch to the already weakened polar vortex, causing the reversal of the polar jet from westerly to easterly right after the first peak of STRAT_K. Therefore, it was the combined effect of the STRAT_J and STRAT_K that caused the first major SSW event in the winter of 2015-16. During the process of breaking up the polar vortex, the STRAT_J transported nearly three times more of warm air into the polar stratosphere that paved the way for STRAT_K to squeeze the polar vortex out of the Arctic completely. STRAT_K1 is the aftermath stratospheric PULSE event associated with relocation of the polar vortex back to the Arctic, which will deliver another round of massive cold air outbreaks in the mid-latitudes within the next few days.
Follow up on Forecasts Made in Previous Weeks:
STRAT_K1 (02/12-02/15), first forecasted on January 22, is coming soon. This is a successful forecast made at lead times of more than 20 days. As we forecasted, STRAT_K1 is mainly driven by stronger wave activities of wave number 2, leading to cold air outbreaks over both continents in the mid-latitudes during 02/12-02/17, which is consistent with the GFS week-1 forecasts for surface air temperature. The GFS week-1 forecasts suggest that the below-normal temperatures will take place mainly over the eastern half of the North America, East Asia and Central Asia.
STRAT_L (02/19-02/26), first forecasted on January 22, is expected to occur on time. As we forecasted, STRAT_L is an extra long-lasting and strong event. The two peaks that we forecasted last week tend to merge into one main peak on 02/21 according to this week’s forecast data. The main peak is expected to be as large as 1.1 trillion tons per day and be driven by stronger wave activities of both wavenumber 1 wavenumber 2. Therefore, we expect massive cold air outbreaks occur over North America first and then spread over both continents shortly. GFS week-2 forecasts confirmed our forecasts by showing that there is a round of cold air surge over eastern North America around 02/20, and then another round of strong cold air outbreaks is expected to take place over the entire North American continent and the mid-latitude regions of Eurasia.
STRAT_M (03/03-03/08), first forecasted on February 4, is still expected to take place during the forecasted time range with its peak around 03/04. Mainly driven by stronger wave activities of wave number 2, the STRAT_M event will lead to cold air surges over both North America and Eurasia during the forecasted time period, as we forecasted last week.