How cold did South Florida get this morning?

No record cold temperatures were broken overnight in coastal Palm Beach County, but the temperature at the airport did read 42 degrees just before dawn.

The record low is 38 degrees in 1903.

And it’s not even the coldest the region has gotten this year. A low temperature of 40 degrees was recorded in January. Miami dipped to 50 degrees overnight, with Fort Lauderdale reaching 48 degrees.

National Weather Service forecasters in Miami said a sheet of cirrus clouds help to keep the mercury from plunging too deep.

Still, it was chilly, and there’s an interesting reason why.

Florida is feeling the caress of an icy finger of arctic air as the polar jet stream for the first time this season plunges deep into the heart of the south.

The dive into more tropical realms means dawn temperatures Thursday in the 40s along the coast and possibly high 30s in more northern and interior areas of Palm Beach County.

Accompanied by a piece of the polar vortex, which oozed free of its spinning stronghold to mosey south, the frigid air mass has added to the longest stretch of below normal temperatures in South Florida all year.

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Today’s high could reach 65 degrees, a full 11 degrees below normal for this time of year. Sunday’s daytime high of 62 was a whopping 14 degrees below normal. Wednesday also reached a high of just 62 degrees.

“The polar jet has stayed north of Florida, but when it comes down, it brings some pretty good arctic air with it,” said Dan Kottlowski, a meteorologist with the Pennsylvania-based AccuWeather. “It’s bottoming out in the Gulf of Mexico and sweeping right through South Florida.”

The jet stream is a narrow river of swift-moving air at about 30,000 feet that generally blows west to east. In winter, when temperature differences between northern and southern regions are the greatest, it can move at more than 200 mph.

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