(12/25/2014 − 12/31/2014)
· STRAT_E is going to peak on January 1, 2015 as we originally forecasted on November 20, 2014 (lead time: 40 days). This event turns out to be the strongest event recorded so far this winter, delivering approximately 1.5 – 1.8 trillion tons of air per day at its peak time into the polar stratosphere. The cold air branch had peaked already (12/29/2014), delivering a net of 17 trillion tons of the polar cold air per day at its peak time to mid-latitudes, responsible for the ongoing major cold air outbreaks over North America and Europe. The STRAT_E is going to have an aftermath minor peak around 01/07. As a result, we will have weak cold air surge events around 01/07. The combination of the ongoing major cold air outbreak events this week and the aftermath weak cold air surge event in the following week will make the first two weeks of January substantially below normal over both continents, particularly North America which has been hit hardest by the cold air outbreaks associated with the main peak of STRAT_E.
· Despite of the anomalously strong intensity of STRAT_E event, the stratospheric polar vortex seems still to survive from it. Therefore, we expect STRAT_F to be on time (no delay), peaking around 01/15-20 as we first forecasted on 12/4. This event is expected to be not as strong as STRAT_E, but is still capable of bringing cold air surges to mid-latitudes in the end of the second week and beginning of the third week of January.
· The fact that STRAT_E failed to lead a collapsing of the stratospheric polar vortex implies that the timings of STRAT_G1 and STRAT_G2, first forecasted on 12/17, are expected to occur a few days earlier. Now we forecast G1 around 01/24-27 (instead of 01/27-30) and G2 around 02/02-06 (instead of 02/04-06), respectively. Nevertheless, we still expect the last week of January and the first week of February to be cold periods over both continents due to back-to-back STRAT_G1 and G2 events.
· The clustering of STRAT events, E, F, and G1 is expected to make the January of 2015 a cold winter month in term of the monthly mean temperature anomalies.
Forecasts Made on December 31, 2014
Follow up on Forecast Made in Previous Weeks:
· STRAT_F event is expected to peak around 01/15-20 as we first forecasted on 12/4. The cold air surge events associated with STRAT_F will be relatively minor in comparison to STRAT_E.
· STRAT_G event, that was first forecasted on 12/17 but split into STRAT_G1 and STRAT_G2 in the last week’s forecast because of the apparent separation of these two peaks, will take place a few days earlier. The peak days for G1 are expected to be around 01/24-27 and G2 around 02/02-06. The last week of January and the first week of February are expected to have below-normal temperatures.
New Forecasts Made on December 31, 2014
· No new forecasts are made in this week.