Wednesday 9 a.m.
Isaac brought very moist air northward from the Gulf states late last week and through the holiday weekend, and this morning is oppressively humid from Boston to Washington, D.C. A very weak front that has served to focus the formation of thunderstorms will drift past the I95 corridor later today to usher in some slightly less humid air. However, the reduction will only take the region back to what typically passes for humid in the summer: dew points between 65 and 70 (they are in the low to mid-70s now). This map shows the dew points as of 8 a.m. EDT. Notice the mid-70s in New Jersey, the drop to the low 60s in northwest Pennsylvania, the upward nudge through the 60s in Michigan and then a drop more comfortable levels in the 50s across Wisconsin.
In the video, we see the shower-producing system in the East, a break to its west, then more thunderstorms moving east from the western Great Lakes. We also look at tropical storm locations and emphasize that for the moment they are nearly stationery (no... stationary).
The National Weather Service has announced the release of an improvement to its GFS numerical model. It was discovered that the model produced forecasts that were cooler and more moist than what actually happened... especially in drought-afflicted regions of the U.S. The problem stemmed from erroneous data about the true condition of soil moisture. The model thus had no way of "knowing" that its initial surface data inputs were wrong.
Later this week we expect to see a split flow pattern aloft. One branch of the flow will come in from the Pacific and go across the Northern states. With no access to arctic air, this setup favors milder-than-average conditions for the North Central and Northeastern states.
Wet weather is coming toward the Northeast, and episodes of rain may be spread out over a two- to three-day period. Supporting this idea is this satellite/radar image from mid-morning Monday showing pockets and bands of rain affecting several areas.
On this map from 10 a.m. ET Thanksgiving Day, you can see the high pressure area that is causing dry and mild weather in the East and the cold front farther west.
During the late afternoon and early evening hours, the cold front of a knife will slice through the turkey and cause it to accumulate 1-2 inches on plates...
This satellite picture shows clouds over parts New York and Pennsylvania, as well as areas of low clouds, fog and snow cover from Michigan to Illinois. Most of the Northeast should have at least some sunshine through Thanksgiving Day.
As we go through the week, the flow aloft over the East will become southwesterly. This will promote a major warmup. This map shows the projected upper-air flow for Thanksgiving afternoon: