MILD WEATHER TO CONTINUE

A prolonged period of mild DEC weather will continue working its way into the eastern US as the week progresses, though cold air over the Great Lakes into New England will likely keep Temps closer to normal for the next few days. Meanwhile, a short wave TROF digging southeastward across the Midwest into the Southeastern US will bring enough cloudiness, showers and cool air aloft to keep Temps near or slightly below normal in the SE US this week. By next weekend, the very mild air over the western and central US will spread eastward – bringing a surge of much above normal temps to much of the nation in the 7-12 day period. A possible storm development near Florida could keep Temps slightly below normal over the state during Week 2.

The global models and their ensembles have come into much better agreement today with the large scale pattern during Week 2 going into Week 3, with a strong TROF expected to move inland from the EPAC into the central US in about 10 days, with colder air behind it. This will set up the upper level dynamics for at least one (1), if not two (2), fairly large storm systems that will form in the lower Plains during Week 2, and will then head towards the Great Lakes and New England in about 12-15 days. Unseasonably mild air will finally overspread the eastern seaboard during Week 2, while more seasonal Temps begin to take hold in the central US and Rocky mountain region. 

It should be noted that the pattern change forecast to develop during Week 2 is supported by the current eastward propagation of a moderately strong MJO in the West Pacific, which will enter Phase 7 and 8 next week as it weakens. (Phase 7 & 8 generally favor colder than normal Temps across the US – assuming there are no other major forcing mechanisms at play.) That said, the details associated with the pattern change remain highly uncertain, which is typical during major pattern changes, and is especially true with the current event as numerous short wave TROFs and forcing mechanisms are impacting the Pacific basin. It is fairly certain, however, that very cold and deep arctic air will not be able to reach into the US before the closing days of DEC as it will take some period of time for the mild air now across Canada to give way to the development of a deep & very cold air mass – and some type of ‘cross-polar’ flow to develop. (NOTE: Regardless of exactly what pattern may evolve in 10-14 days, the GFS was clearly ‘ahead’ of the EURO and all ensembles again in calling for this longer range pattern change. Impressive, since the ECMWF is ‘known’ for its superiority with such patterns changes in the longer ranges.)