Sunday, July 13, 2014

The Definitely NOT Polar Vortex And The July Chill In The Great Lakes

Chilly for July, but nothing like this. So relax and enjoy.  
I've been struck by how many weather watchers, geeks and bloggers have been more excited to inform us that the current cool spell in the upper Midwest is NOT the polar vortex, and less excited to tell us just how cool it is.  

"Polar vortex" came into the national vernacular last January, when a sharp cold snap, caused in part by a spinning upper level low pressure system that drifted much more south than usual, got everybody both shivering and all warm and gooey with the new weather term.

Turns out, the weather term isn't all that new. A polar vortex is a normal feature in the high Arctic much if not most of the year, and that January cold wave wasn't really a true polar vortex getting lost.

After that chilly January week, every hint of chill has been referred to in some circles as the polar vortex. Same with this cold wave at a time of year when we don't have cold waves that often.

The Weather Powers That Be have been sounding the alarm for days now: Don't call this the polar vortex because it's not. The chill is almost besides the point.

They're right. This is just an unusual southward dip in the jet stream causing the cool weather.  Believe it or not, a typhoon that hit Okinawa, Japan last week is partly the cause of this cool spell. The typhoon pushed the jet stream far northward out ahead of it, which helped make the entire jet stream temporarily wavier than usual for July in the Northern Hemisphere.

That means a big push of hot air way into northwestern Canada, and the big southward dip in the jet stream that is giving the Continental U.S. it's current cool spell.

To be honest, it is a pretty sharp cold wave for July, but it's not unprecedented. The worst of it will hit Upper Michigan, where the next couple of days will feature high temperatures only in the 50s. But it's been that cold there before in July.

There might be a smattering of daily record low temperatures during this, but I doubt there will be all-time record lows for July.

The cool spell is probably welcome in the South, where it will push a cold front much further south than they normally get this time of year.  In Oklahoma, where temperatures are routinely in the 90s to around 100 this time of year, high temperatures midweek should only make it into the 70s.

The push of cool air will sort of run out of gas as it approaches the East Coast, so the Northeast will get what will be some nice, refreshing air, but not an unusual cold snap.

Here in Vermont, for instance, high temperatures during the second half of the week will be in the mid 70s, which is only about five degrees cooler than normal.

The big problem with this cool air is it's invading the normal hot, humid air that usually sits over the country this time of year. The invasion looks like it will set off another outbreak of severe thunderstorms today through Tuesday in parts of the Midwest and Northeast.

Today, Sunday, the severe storms will be most focused from western New York through the Ohio Valley and on toward Illinois, the same areas that got hammered last Monday and Tuesday by wicked storms.

Monday, the worst of the storms will hit from the Mid-Atlantic area back into Tennessee.

This July cool spell won't last long in most places in the country.  By next weekend, almost everyone in the nation will be at least starting to approach normal July temperatures.

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