Monday 10 a.m.
Tropical Storm Alberto formed off the south Atlantic coast during the weekend but it is not having any direct impact in the Northeast. However, with a high pressure area retreating from northern New England and a low pressure area over southeastern Virginia, an east to southeast flow of increasingly moist air is affecting the region. At 8:30 this morning, a band of heavy rain with embedded thunderstorms stretched from northwest New Jersey to the waters east of Monmouth County, N.J. Many places between Newark and Somerville, N.J., had more than half an inch of rain in just a few hours this morning. Closer to Philadelphia, there was nothing. However, a large batch of rain and thunderstorms was just off the coast of southern New Jersey and was moving northwestward.
This video should give you an idea about what to expect during the course of the week. One trend we expect is for showers and thunderstorms to become more spotty as we go through the middle of the week, and for most of them to occur during the afternoon and evening hours.
This map showed the pressure pattern at 9 a.m. EDT Monday. You can see the east to southeast flow that was bringing ocean air ashore in the Northeast. Also, the NNE-SSW orientation of the isobars was causing clouds to linger on and near the west shore of Lake Michigan.
Here's a cool fact: even when Death Valley, California, has a temperature of 110 or 120 degrees, you only have to go up a little more than 3.5 miles to find temperatures at or below freezing.
It appears the dry comfortable air mass now in the Northeast will be replaced by a humid flow from the South Atlantic states for the coming weekend. An upper-air forecast map sequence in the video shows how this could happen. The following map shows the predicted flow from Florida to New Jersey Friday night.
This map shows the pressure analysis for the Northeast and Great Lakes. The gusty flow on the west side of the low pressure area adds a real autumn feel to the air.
Since individual lines and clusters of thunderstorms have limited life spans and change character constantly, forecasting whether it will or won't rain at any one time this weekend is difficult at best. One solution is to have your tablet or phone available with the AccuWeather.com app so you can see where all the storms are at the times when it concerns you the most.
It does look warmer for the weekend, but every time the warm air tries to extend into New England it gets chopped down. There could be more showers at times Sunday and early next week as forest we can tell. If any forecast gives you a headache, why not take a friend's advice: Take two aspen; sequoia in the morning.
This map from 5AM ET shows the cold front that is continuing toward this Northeast and Middle Atlantic states. Temperatures stayed up in the 70s all night ahead of the front but it turned noticeably cooler after the front moved through.