Heat Wave Ending (Updated 720 PM 9/26)

The heat wave is coming to an end as cooler air gradually moves into the region tonight . Cooler, and less humid conditions will then prevail for the rest of the work week.

See below for the record highs for Milwaukee and Madison between 9/20 and 9/26. The values in red are new record highs from this current warm spell:

Why the warm weather?

This image below shows 500 millibar heights, which is basically nerd talk for atmospheric pressure around 20,000 feet up in the sky. We look so high up because what goes on at this level often drives the weather we experience at the surface. The contours show the wind direction and it is from the southwest in our region. This is bringing the warm air into southern Wisconsin. High pressure sitting just to our south will contribute to the continued dry weather.

500 millibar heights. Basically atmospheric pressure at 20,000 feet.

Further west, notice the area of low pressure. It is embedded in a trough, or U shaped flow. North winds from Canada will be bringing cooler air down the west coast and across the western U.S. In fact, snow has fallen across the higher elevations of the Rockies with this system, and more is forecast over the next few days.