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 will determine 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.
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