Tuesday 9 a.m.
The upper-air current arriving in Pennsylvania this week originates over the Gulf of Mexico, so it is no surprise the main weather theme is warmer and more humid than typical for the season. However, computer models suggest that on Sunday, the flow reaching Pennsylvania will have originated in western Canada. Translation: warmer, then chillier. This video has more:
The details of the weather pattern are far less clear-cut than the overall trend. For example, there has been rain, some heavy, in a corridor extending from Pennsylvania to Virginia. Pittsburgh has been near the western edge; Philadelphia just east of the eastern edge. Farther south, violent thunderstorms developed in east-central North Carolina. Here is a map showing where precipitation was at 10 a.m. EDT.
This year, the "slight" category has been divided in two: slight and enhanced. When seen together on an SPC map, the progression makes sense. When the term "enhanced" is used alone, it can be a challenge, at least until we get used to it.
This map shows the pressure analysis and locations of fronts and low pressure areas at 9 a.m. EDT today. Places from Philadelphia northeastward will only warm up if and when the warm front in Delaware passes any given spot. Chill air follows the front in Indiana.
This map shows the GFS forecast for Monday at 2 p.m. ET. If correct, rain will hold off for the Boston Marathon. However, you can see that any speedup of the rain would prove that idea to be wrong.
Another high pressure area will build over the Northeast during the weekend, so sunshine with mild afternoons can be expected. However, this forecast map for next Monday evening shows how extensive and wide ranging the next storm may be.
These maps show how the US model handles the disturbance now causing rain in Tennessee. On the 1st map (for tomorrow), it is embedded in a southwesterly flow. However the 2nd map (for late tomorrow night) shows it turning more toward the course that would take it out to sea.
In the middle of Pennsylvania, rain ended before daybreak, but rolls of sullen clouds presided during the first hours of daylight. A robin takes in the scene.