An eastward shift of the Madden Julian oscillation from the equatorial Pacific Ocean into the Atlantic in the 6-10 day period coupled with a stratospheric warming event over northern Canada next weekend forces arctic air formation in south-central Canada this weekend released into the West and Central U.S. early next week. The air mass races into Texas moderating south of snow cover nevertheless having quite a cold punch. Eventually, the air mass shifts into the East days 11-15. An expansive U.S. snow cover evolves during the period.
So far, despite brief periods of cold the U.S. is super warm for December 2017. The second half of the month according to the midday operational GFS (model) as depicted by Storm Vista Weather Models indicates eastern Canada turns frigid but most of the U.S. remains warmer than normal. What climate factor is the leading cause of the warm start to winter?
The historic 2010-13 cool phase of the PDO was followed by an even more impressive warm phase (2014 into 2017). The extreme PDO signature has ended. Analogs indicate neutral phase will continue for 2018. The analogs indicate that nationally a drier than normal climate will evolve which the 90-day precipitation trend is indicating that potential scenario has already developed.
Earlier in today's forecasts we mentioned stratospheric warming over northern Canada causing some extreme cold into the northern U.S. Christmas week. Now let’s evaluate the role of the MJO. The MJO forecasts vary but Climate Impact sides with the persistence forecast (GFS) for days 4-8/6-10 followed by a progressive MJO toward the Atlantic (as indicated by the ECMWF). The implications are an eastward shift of the anomalous warmth anchored West (recently toward the East Coast while the cold pattern in the East retreats to snow cover. In the 11-15 day period the MJO shift s to the Atlantic and coupled with stratospheric warming leads to an arctic outbreak into the Central U.S. Briefly very warm East ahead of that cold air.