Wednesday 9 a.m.
A wide zone of cloudiness that includes patches of showers and some thunderstorms now stretching from Lake Superior all the way to Georgia is moving east. The greatest chance for the heaviest rain from D.C. to New York City will be during the day tomorrow, then tomorrow night in Providence and Boston. Various computer models present widely varying views of the timing. In the Washington area, GFS shows the heaviest rain coming in the afternoon, whereas the NAM-WRF model has most of it in the morning. The European model has rain predicted throughout the day tomorrow. However this turns out, it seems like tomorrow would be a fine time to carry, and at times use, rainwear.
This map shows the projected total rainfall between Wednesday morning and Friday afternoon. The heaviest rain predicted is just over 2 inches not far from Philadelphia. With more than 13 inches, this was the wettest July in the history of record keeping for the city. The rainfall pattern was not uniform, and some northeastern parts of the city got less than half this amount.
This map is a rainfall forecast from the NWS Middle Atlantic River Forecast Center located in State College, PA.
The upper-air flow forecast for this evening shows the trough that helps to support rainfall ahead of the cold front.
After reaching the 80s today from NYC to Boston, it might not be that warm again through much of next week.
A noticeable push of cooler air will spread southward from Ontario and Quebec into the eastern Great Lakes and New England between tomorrow and Saturday.
A cold front from eastern Canada will slide southward along the East coast between late Friday and the end of the weekend. For the area from Philadelphia to Boston, where temperatures will reach the summery 80s each day through Friday, it will mean a noticeable change to cooler weather.
Average high temperatures in Chicago and New York City are in the mid-70s now, but for the next several days, temperatures will run 8-15 degrees above those long-term averages. Supporting this warmth is a flow aloft that originates over the Southwest: