Wednesday 12:15 p.m.
During the next couple of days, the driest air mass in weeks will spread across the Great Lakes and into the Appalachians. However, its advance is likely to slow then stall near the East Coast. This video shows why this should happen.
The map shows how wet and dry areas may be arranged on Saturday afternoon. It doesn't show excessive rainfall but suggests the driest weather will stay west of the Appalachians.
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).
This map, which is updated frequently, showed our track forecast and main impact notes as of 10 AM ET.