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.
Looking ahead to late next week, some of the computer models suggest a hurricane could affect areas between the Gulf of Mexico and the Atlantic east of the Bahamas. We are entering the prime part of the Atlantic hurricane season, but at this point there is only one model I am prepared to accept:
The following map shows the individual members of the forecast for the 5,880-meter height line at 500mb. If the 500 mb height is that high, it usually means the weather at the ground in the Northeast is hot. However...
This pressure analysis was made using 9 a.m. ET data. The thin west-east black line is the boundary between hot and cool weather. A low pressure area is moving eastward along the boundary zone, causing showers and thunderstorms. The next low pressure area should send some of the rain farther north.
In the early to middle parts of next week, we expect to see a boundary zone separating hot, humid air to the south from cooler air to the north. A series of ripples or disturbances aloft moving west to east will take turns at enhancing or reducing the chance of showers and thunderstorms.
Looking beyond next week, we see signs of something that has been missing in the Great Lakes and Northeast just about all summer: hot weather. That may change. Here is a computer model prediction of the upper air flow on Sunday, Aug. 24. Note how the flow appears to run from Arizona all the way to north of New England.
The following regional radar map shows that while there are not any large shields of steady rain, there are pockets and bands of rain and thunderstorms that contain heavy precipitation.