New Forecasts Made on December 23：
In this week’s forecast, we are forecasting a new event, named as STRAT_J, to occur during the period of 01/21-01/27. STRAT_J looks to be a relatively weak event with multiple peaks. The associated cold air outbreaks will occur over both North American and Eurasian continents.
The stratospheric polar vortex may not break completely till the J event.
Since December 3, 2015, we have been forecasting a minor and short-lasting breakup of stratospheric polar vortex to occur in 01/6-01/12, 2016. Since none of the four consecutive stratosphere PULSE events, namely STRAT_E, F, G, and H, are super strong events (i.e., the peak intensity is weaker than 1.0 trillion tons per day), it needs more STRAT PULSE events to bring warm air into the polar stratosphere to cause a complete breakup of the polar vortex (i.e., the dominance of easterlies surrounding the Arctic instead of westerlies). Nevertheless, the vortex will be significantly weakened after STRAT_H event. The center of the polar vortex will be pushed away from the Arctic during the period 01/08-01/12, 2016. In the next two weeks, the vortex will keep wobbling due to STRAT_I and J events and is expected to eventually break up after the J event. Cold air outbreaks associated with STRAT_H and J will affect both continents more equally, whereas STRAT_I is going to mainly impact North America. Despite we are experiencing a super El Nino this winter, we expect that these three STRAT PULSE events (H, I, and J) are still capable of bringing freezing temperatures to a nearly 50% area over both continents.
Follow up on Forecasts Made in Previous Weeks:
STRAT_F (12/19-12/24) has taken place as we first forecasted on November 13, with a lead forecast time of more than 1 month. At the peak day of STRAT_F (December 22), more than 0.9 trillion tons of warm air mass was transported into the polar stratosphere. STRAT_F, together with the third main peak of STRAT_E, caused major cold air outbreaks over both continents from 12/16 to 12/21. Due to the super El Niño, most areas in mid-latitudes are going to be warmed up by the Christmas Eve, as we forecasted last week.
STRAT_G (12/25-12/29), first forecasted on December 3, will peak around 12/28 and we continue to forecast it as a weak event in this week’s forecasts. STRAT_G will lead to another round of mild cold air surges mainly into North America in the week after the Christmas.
STRAT_H (01/02-01/08), first forecasted on December 3, is still expected to on time. The twin peaks of STRAT_H are expected to occur on 01/02 and 01/07, respectively. Therefore, surface air temperature is going to decrease over both continents in the first week of 2016.
STRAT_I (01/13-01/19), first forecasted on December 11, is still expected to occur within the forecasted time range. STRAT_I is not an extremely strong PULSE event. Thus, we expect the intensity of this round of cold air surges will be moderate as well.