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.
map shows predicted rainfall between now and next Wednesday. This will need to be watched in order to assess the risk of flooding.
Looking farther ahead, it appears a summer version of THE POLAR VORTEX will send much cooler air into the Great Lakes and then the Northeast. The first map shows the flow aloft next Tuesday night. The second map shows what could be a heat wave a week and a half later!
There were numerous thunderstorms yesterday. This is the lightning stroke map covering the period from 8 ET yesterday morning to 7:30 ET this morning. Thunderstorms will be less numerous today, but any that do form can cause briefly strong and gusty winds.
One area of concern is Lake Erie, where unprepared boaters could suddenly be blasted by 60-mph winds. The National Weather Service Storm Prediction Center has outlined a large area where the threat of strong wind exists. The map is below today's forecast video.
Tomorrow, a cold front will cross the Great Lakes, then reach the Northeast by the end of Wednesday. Today, a southwesterly current of very warm air is evident on the surface pressure map.
The center of Arthur (shown here at noon ET) should pass less than 50 miles southeast of Nantucket this evening, causing heavy rain and gusty winds across much of eastern New England. Meanwhile, the Great Lakes and much of the Appalachian region have a lovely Fourth (but take a jacket or sweater as you head out to the fireworks).