Bolaris: Another 'Polar Vortex?'

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A man walks through the rain in Franklin Delano Roosevelt Park, in Philadelphia, on Tuesday, June 18, 2013. ( Stephanie Aaronson / Staff Photographer )

Though we've been hearing the past few days about "the return of the Polar Vortex", you can rest assured there is more pressing weather on the way.

The National Weather Service has issued a severe thunderstorm watch through 8 p.m. for several counties in the region including Philadelphia, Montgomery, Bucks, Chester and Delaware counties. 

The launch of severe cells for the Philly region are dropping southeastward from our northern and western suburbs. The best chance of severe storms is during maximum heating in the late afternoon and evening hours.

A flash flood watch is also in effect through tomorrow evening. Indeed, tomorrow we will see a widespread lashing of heavy rain and possible storms will result in high probability of flash flooding and plenty of street and highway floods. The result could be one to three inches of rain.

The atmosphere will stabilize on Wednesday. Dry air will take over as the rain and storms nudge off the coast.

That brings us to the so-called Polar Vortex. The term makes for interesting weather headlines, but it is misleading. Let me explain.

Yes, the coolest air mass of the season is dropping down across the upper Midwest and, by summer standards, could set records. Temperatures across the upper Midwest in towns like Chicago and Detroit will see temps drop 10-20 degrees below normal.

That massive pool of cool air will drop southward from the Northeast Pacific. But it is not the same polar vortex that originates from Hudson Bay in Canada that resulted in those big winter snows in the East. The polar vortex is a cyclonic, ultra-cold storm stacked well into the atmosphere.

This summer system is different, though it will produce unusual cold across the upper Midwest and ignite severe storms along its leading edge into the Northeast and Mid-Atlantic later this week.

The battle zone between the dynamic cooling arriving from the west occurs when the mass collides with very warm and unstable air as it flows to the east. The result could cause multiple rounds of severe storms and flooding in our backyards.

So it's not really the Polar Vortex, but rather a massive pooling of unseasonably cool air that has potential to create headaches for the entire Delaware Valley.

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