Tuesday 7:15 a.m.
My video shows the heat wave setup for the northeastern third of the country and explains why the heat wave should be cut down during the coming weekend.
The map showing today's upper air flow pattern includes a huge high pressure area aloft centered over Ohio. This kind of high is a classic signature for a heat wave. Note how the prevailing westerlies are pushed well north into Canada.
Most of the time when a big ridge is in charge, there is little or no precipitation. Air sinks in high pressure areas, and sinking air becomes warmer and drier. Yesterday, thunderstorms were most numerous in the Southeast and back into Texas, well south of the high pressure center. However, the hot air mass is so humid that some thunderstorms popped in response to intense ground-level heating right into the central part of this high pressure area.
This forecast map of the upper air flow for Saturday shows a big high is gone and the westerlies are expanding southward through the Great Lakes region. This strongly suggests a cold front will be moving into the Northeast with thunderstorms (perhaps severe) followed by an end to this heat wave.
This table shows the ensemble means for the next two weeks at Philadelphia: It suggests that whereas it does turn cold, any snowfall looks quite limited.
It is too early to be confident about any forecast for Christmas Day (or even the week before). However, the GFS model does go out 16 days, and it has a cold look for the Northeast exactly one week before Christmas.
As the flow aloft becomes southwesterly, mild moist air will spread northeastward from the Gulf States. In summer, this creates a hazy, very warm and humid scene for the Northeast. Now though, the warmth is slowly drained away as the moist mild air advances over cold ground. With temperatures near the saturation point, clouds form.
If each one of us lights an inner flame for just one thing- just one aspect of our lives we are thankful for, the warmth we create can light the world on Thanksgiving. The flame of warmth and love can burn so bright that no cold wind on earth can blow it out.
One concern for later this afternoon and evening is a trailing batch of precipitation moving northeast from the Carolinas. If this survives to reach the I-95 corridor just as the cold air arrives, there could be a brief but nasty episode of snow that makes it slippery.
The exact placement of the storm center will determine who gets into the real warm air coming up on the east side of the storm and who stays in the chilly air on the west side.