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Tuesday 8:30 a.m.
Drier air advanced into the northeast quarter of the nation yesterday, but its tenure is temporary and will be quickly terminated. As a high pressure area moves off the East Coast and a low pressure area forms near the lower Great Lakes, more humid air will be drawn northward... and the chance of showers and thunderstorms will increase. This looks like the kind of setup that can unleash 1-2 inches of rain in some areas. However, until we see exactly where the storm forms and how the moisture becomes arranged around it, forecasting rainfall amounts for various places is risky. The video has more.
On this date in 1918, Philadelphia had a high temperature of 106, the highest official reading ever for that city. What did the weather map look like that day? NOAA maintains an archive of weather maps for each day back to 1871. You can view them here The map for Aug. 7, 1918 is below. The map time is 1 a.m., and you may be able to see the 80-degree isotherm for that hour.
In those days, weather records were kept at the Customs House in Center City, Philadelphia. In later years, the observation site was shifted to Philadelphia International Airport. Airport locations are typically somewhat cooler than the middle of our big cities.
Snowfall amounts yesterday were low from Philadelphia to New York City. Accumulations increased toward the north and northeast.
This map shows the NAM's projection for this Friday night. The isobaric pattern suggests there is a southwesterly flow of mild air from the Gulf states to the Middle Atlantic region. Farther north, we see evidence of the frontal boundary that separates the mild air from chillier air.
A new area of snow now over southern Minnesota should expand southeastward to reach Chicago this afternoon, streak to Pittsburgh this evening, then reach the Philadelphia/New York City area late tonight or early tomorrow morning. This map shows a low pressure area over Missouri.
This map shows expected accumulations.
Check AccuWeather.com's latest info as the forecast ideas mature. This is a draft of the Thursday morning snow accumulation idea.
Here is one snapshot from this morning's NAM run, depicting the precipitation it predicts for Saturday between 1 and 7 p.m. ET. The rain/snow line should be close to the Pennsylvania-Maryland border.