The Importance of the Polar Vortex Right Now

January is the coldest month of the year for a majority of the nation. 

A Polar Vortex (PV) is a persistent large-scale cyclone that can exist in the middle and upper atmosphere at one or both of the earth’s geographical poles. The core of coldest air is usually associated, and confined, to the region within the PV.  The vortex is the strongest in winter and can disappear in summer.

The PV is not always symmetrical in shape.  It can, and often is, elongated in shape — dipping southward across the Upper Midwest, Great Lakes, and eastwards into the Ohio Valley and parts of the eastern U.S. These “lobes” also rotate around the primary core vortex which can be anchored well to the north. As each rotational lobe dips south cold arctic air is reinforced.

The PV is not always symmetrical in shape.  It can, and often is, elongated in shape — dipping southward across the Upper Midwest, Great Lakes, and eastwards into the Ohio Valley and parts of the eastern U.S. These “lobes” also rotate around the primary core vortex which can be anchored well to the north. As each rotational lobe dips south cold arctic air is reinforced.

When the polar vortex is strong, the jet stream is anchored further north which tends to contain cold air resulting in milder weather over much of the U.S.

When the polar vortex is weak, the jet stream dips south allowing cold air to sink over parts of the eastern U.S. 

January Outlook

Right now, the PV is stable and relatively strong, confining the coldest air mainly within arctic regions. For the rest of January, this stable pattern will set the stage for persistent temperature anomalies — unusually-cold air over the Northern Plains and unusually-mild over the Eastern U.S.

Note the anticipated persistence of these strong temperature anomalies for at least the next 2 weeks

Active Weather Ahead

There will be a strong boundary between these contrasting air masses. Active weather is likely along this boundary with an enhanced risk for severe storms, heavy rain, and flooding.

In fact, a very potent storm system will impact parts of the eastern U.S. later this week into the weekend.

 

Heavy Rain Threat Next 5 Days