Big Change Next Week

Thursday 10:30 a.m.

The high pressure area sponsoring sunny, warm weather in the Northeast now will be replaced by a cooler high pressure area from the Plains for the weekend. Meanwhile, we see a strong jet stream current coming into western Canada. As a ridge builds farther west, the current will be sent southeastward, and this should carve out a strong, chilly trough that will be over the Great Lakes by next Tuesday or Wednesday. Ahead of the strengthening trough, moist air from the Gulf states should flow northward. This could set off an area of significant rainfall between the Ohio Valley and East Coast before the cool air at ground level reaches these places. This video presents the general idea:

This map shows the detailed pressure pattern across the Northeast and Great Lakes this morning. The isobars extending from Kentucky to New York state show the southwesterly flow of warm air. The bend in the isobars (one in Missouri and the other in Michigan) shows the front that separates the warm air from the advancing cooler air. The flow is out of the north across much of Wisconsin.