New Forecasts Made on December 17：
No new event is forecasted in this week’s forecasts.
Continue to forecast the first breakup of the 2015/16 stratospheric polar vortex to occur after STRAT_H (01/06-01/12)
We continue to forecast the 1st breakup of the 2015/16 stratospheric polar vortex to occur right after STRAT_H, as we first forecasted on December 3. The successive four stratospheric PULSE events, STRAT_E, F, G, and H have been transporting anomalous more warm air mass into the polar vortex core in the stratosphere for a month, filling in the polar vortex at a rate much higher than the radiative cooling rate and gradually eroding the polar vortex. In particular, the two pronounced PULSE events (STRAT_F and H), powered by stronger wave activities of wave number 1 and 2, first cause the vortex off-centered the Arctic and then split into two pushed away from the Arctic. The latest GFS forecasts have already indicated that a pocket of warm air will first get into the Arctic on December 30. Nevertheless, we note that none of the PULSE events that have happened or forecasted so far in this winter are remarkably stronger than those last winter. Therefore, the polar vortex may be restored back to the Arctic very quickly. For this reason, we expect the 1st breakup of the 2015/16 stratospheric polar vortex to be minor and short-lasting. In addition, we still cannot rule out the possibility that the first breakup could be delayed after the STRAT_I event, as we reported last week. Associated with the first breakup of polar vortex, there will be several rounds of large-amplitude cold air outbreaks in the first two weeks of 2016, affecting most regions in both continents.
Follow up on Forecasts Made in Previous Weeks:
STRAT_E (12/11-12/16), first forecasted on November 12, have been materialized. The second and third main peaks of STRAT_E have already occurred on 12/12 and 12/15 respectively. These two peaks of STRAT_E have led to below-normal temperatures mainly over the regions of East Asia and the western half of North America.
STRAT_F (12/19-12/24), which was first forecasted on November 12, is going to occur on time. STRAT_F, powered by stronger wave activities of wave number 1 and wave number 2, will transport more than 0.7 trillion tons of warm air mass per day into the polar stratosphere. STRAT_F, together with the third main peak of STRAT_E, is expected to cause major cold air outbreaks over both continents. For North America, waves of cold air temperature will move through the whole continent. The impact of STRAT_F on Eurasia, which will be mainly over East Asia, is expected to be less severe.
Cold surges associated with STRAT_E and STRAT_F could affect the pre-holiday travel. However, most areas in mid-latitudes are expected to be warmed up soon, which is due to a super El Niño this year.
STRAT_G (12/25-12/29), first forecasted on December 3, is still quite weak in this week’s forecasts. But it is coupled with a stronger cold air mass transport out of the polar region near surface, thus associated to another round of mild cold air surges mainly to North America in the week after the Christmas.
STRAT_H (01/02 -01/08), first forecasted on December 3, is still expected to take place as we forecasted. The twin peaks of STRAT_H are expected to occur on 01/02 and the other on 01/08, respectively. The first peak is mainly due to wave number 1 while the second one is mainly contributed by wave number 2. The successive stronger wave activities may lead to temporary short-lasting split of the polar vortex. Therefore, colder air is expected to return to both continents in the first week of 2016.
STRAT_I (01/13-01/19), first forecasted on December 11, is expected on time. It is highly possible that STRAT_I is not as strong as we forecasted last week since polar vortex may break up before it. We expect this round of cold air outbreak events will be felt strongly over both North American and Eurasian continents.