Cool air dominates the Northeast while a heat wave is unfolding in the Central Plains. As we go through the week, an upper air trough from just off the West Coast will move to the Rockies and then the Plains. A ridge now over the Upper Mississippi Valley will reach the East Coast Friday night. The position of the upper air ridge axis will be important later this week because it determines how far the very warm air will progress. In a true warm sector, where the air is uniformly warm, the flow at ground level is parallel to the flow aloft. That will be the case west of the ridge axis (or crest). Downstream from there the surface flow may be from the southwest but the flow aloft is from the northwest. When the wind changes in that way with elevation, it is called a veering wind. In such cases, it is becoming warmer, but may not yet be anywhere near as warm as in the warm sector I mentioned earlier. It is in the contested zone where we look for clouds, showers and thunderstorms. This video forecast extends through next weekend.
The sun must be low in the sky for rainbows to appear, when showers move east of your location and the sun comes out, a rainbow often appears. Here's a partial rainbow I saw Saturday evening.
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:
A major snowstorm will affect the area from Iowa to Michigan tonight and tomorrow. At first, snow can melt on streets, but as it continues and the temperature drops, the area impacted by slippery conditions will increase dramatically. This map shows expected accumulations: