View from the top of the world (H. Michael Mogil, CCM, CBM, DMS)
I decided to use NCEP forecast upper level (Fig. 1) and surface (Fig. 2) maps for Jan. 7, 2017 (eight days into the future) just because the patterns on these maps would be the easiest to explain. There are three important observations that I’d like to share.
First, the jet stream (a long, thin ribbon of high altitude, high speed moving air), shown by shades of blue, extends in a more-or-less continuous band around the globe. However,
there are times when the jet stream exhibits a more broken pattern. In general, the jet stream separates colder air on its polar side from warmer air on its Equatorward side.
Second, the jet stream exhibits dips (troughs or low-pressure areas – shown by orange lines in Fig. 1) toward the Equator and bulges (ridges or high-pressure areas) toward the pole. Associated with these upper level features are matching surface features (typically displaced slightly to the east of their upper level counterpart). Most of the upper level troughiness and most of the surface low-pressure systems lie within the 45 to 60 degree North latitude band. This is slightly south of the climatologically-preferred latitude.
Third, the “polar vortex” is not a single upper level low-pressure system, but rather a large zone (covering much of the high latitude region) with many low-pressure systems within it. These low-pressure systems rotate in a counterclockwise sense (west to east) around the overall “vortex” center. Here, one larger lobe of the “vortex” covers much of Canada.
The troughs noted under item two above actually appear like spokes on a wheel, as they, too, rotate around the main polar vortex circulation center.
Given this “polar vortex” and jet stream pattern, northern states will continue to be ruled by cold air, while southern states will enjoy well-above average temperature readings. In between, warm and cold air will battle for control, with a much more changeable weather pattern.
NCEP’s eight- to fourteen-day forecast (Fig. 3) shows this overall pattern. The only exception is that below average readings should trend further southward thanks to more troughiness in the west, an expected slight jet stream dip southward, and the further southward displacement of cold surface air.
Finally, the storm track suggests that the Northeast will be the recipient of the most stormy weather action. Based on details of longer range model forecasts (not shown), more meteorological “bombs” (very rapid low-pressure deepening) are coming.
© 2016 H. Michael Mogil
Originally posted 12/30/16