Southeast ridge will flex its muscles late month

All things considered, after much conversation and discussion, meteorological winter came in cold and active during the month of December. Multiple shots of arctic air and several winter weather events, particularly in the interior, have given us a December much different than the past few years, when warm air dominated the Eastern United States’ weather pattern. That very same cold and active pattern looks likely to take a hiatus over the next few weeks.

The hemispheric pattern is undergoing changes once again — this time, pulling back the reigns on an active, amplified pattern which saw polar air drop into New England last week. This time, the stratospheric polar vortex will tighten and strengthen near the North Pole, pulling back much of the arctic air and reforming the vortex near its usual whereabouts. For much of the Northeast US, this means that arctic air will gradually become less available over the next two weeks.

gefswarm

Exacerbating the issue will be the development of troughing from Alaska into the Northeast Pacific Ocean — occasionally shifting into the Western United States. That type of weather pattern tends to favor storm systems and disturbances dropping into the Western USA and ejecting northeastwards. But without any blocking, and the stratospheric polar vortex strengthening, a Southeastern US ridge is likely to develop.

While the active storm track is likely to continue with the Pacific jet stream staying energized, disturbances are likely to track into the Western USA and then eject through the Central US. In the Northeast US this is a warmer pattern, with above normal air and more difficulty attaining widespread winter weather like much of the area saw on Saturday morning.

Forecast model guidance has caught on to the developing pattern, with both the ECMWF and GFS operational and ensembles suites showing the development of above normal temperature anomalies in the Eastern US by the end of December. This looks likely to peak around Christmas — ironically, the same time as some of the past few seasons — but may continue well into the first week of January.

GEFS Ensembles showing temperatures moderately above average for a 5-day average period ending January 2nd, 2017.

GEFS Ensembles showing temperatures moderately above average for a 5-day average period ending January 2nd, 2017.

Warmer than normal air doesn’t mean winter weather is impossible in the Northeast; in fact, a Southeast Ridge can serve as a highway for storm systems on its northern periphery. But it does mean that widespread winter weather will be harder to come by, especially along the coastal plain where the lack of cold air supply becomes a large mitigating factor.

Stay tuned over the next few days for more information on the evolving pattern. Tomorrow’s products will include a video discussion, a look at individual storm systems ahead, and ideas as to when the warmer pattern will break (hint: we don’t think it will last all that long). Have a great Sunday evening!