Consider this Christmas cool-down a gift from Mother Nature, with temperatures forecast to dip into the low 60s this morning and the mid-70s this afternoon.
It should be a refreshing change after two nights of record heat earlier this week, where readings were about 15 degrees warmer than normal. But it won't last -- temperatures are expected to climb to near 80 degrees by Thursday and over the weekend.
Blame, or credit, the unseasonable heat on a persistent high-pressure area east of Florida, over the Atlantic. It has resulted in winds coming from the south and southwest.
That, in turn, has directed heat from the interior of the state in this direction, said meteorologist Chuck Caracozza, of the National Weather Service in Miami.
"High pressure itself doesn't create the heat because you can have high pressure and cold weather," he said. "It's the direction of the winds that influences our temperatures."
If the existing high pressure system was to our north or northwest, it likely would deliver cool or cold weather, added meteorologist Robert Molleda.
Usually, South Florida has had two or three bouts of chilly weather by this time of year, but the only real shot of cold air arrived on Thanksgiving, when temperatures dropped into the 40s and 50s.
Much of our winter weather is determined by how often cold fronts cascade in this direction and how strong they are when they arrive.
While even the strongest fronts are diluted by South Florida's subtropical climate, some are blocked by high pressure systems before they get this far. That has been the prevailing pattern during the fall and winter, Molleda said.
Jim Lushine, a retired weather service forecaster, said the cold air that reaches South Florida comes from one of three sources: the North Pacific Ocean, southern Canada and the arctic regions of Canada and Alaska.
"The coldest air comes from the arctic," he said.
In much the same way hurricanes are steered by winds, cold air masses often are guided by the jet stream, an upper level fast-moving river of air over North America.
"If the jet stream dips far enough south, due to a sharp trough of low pressure, the cold air will plunge through South Florida," Lushine said.
The Bermuda High, well known to South Floridians for either guiding hurricanes toward or away from us, is among the high pressure areas that prevent cold fronts from reaching this region, Lushine said.
"A strong high blunts approaching cold fronts and moderates temperatures, especially at night," he said.
Earlier this week, overnight lows were in the mid to upper 70s, breaking heat records. On Monday, the low was 77 in both West Palm Beach and Fort Lauderdale, breaking the previous record of 75 set in 2006 for both cities. The low was 76 degrees in Miami, breaking the previous record of 74, set in 2006.
The weather service's long-range forecast calls for temperatures to be about normal through February, leaving open the possibility for freezing conditions.
Lushine noted that being "warm and cozy" isn't such a bad thing, considering much of the nation is blanketed in snow and ice during the winter.
"Wouldn't it be nice to have a quiet hurricane season followed by a mild winter?" he said.
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