Heat Departs, Rain Returns for East, Midwest

By , Expert Senior Meteorologist
July 20, 2013; 1:50 PM
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Soon after the heat wave ends in the East and Midwest, the pattern of frequent downpours and the potential for flash flooding will return.

The area of high pressure responsible for the heat wave this past week will be replaced by a weather pattern favoring lower temperatures. However, humidity levels will come back rather quickly.

The pattern will tend to flip back to what occurred during much of June into the first few days of July; almost daily rounds of showers and thunderstorms.

While the heat wave allowed the ground to dry out and stream levels to drop a bit, persistence of the wet weather for next week and possibly through much of August could lead to renewed flooding problems in some locations.

Despite less rain this past week compared to earlier in the summer, many locations in the East have received double their normal rainfall since June 1. Cities with close to two-times their normal rainfall include Boston (11 inches), Philadelphia (12 inches), Washington, D.C. (14 inches), Atlanta (14 inches) and Raleigh, N.C. (12 inches).

The majority of locations in the Midwest have had above-average rainfall as well including Chicago (7 inches), Detroit (9 inches), Cleveland (11 inches), Nashville (10 inches) and Minneapolis (8 inches).

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The most likely issues would be highly localized flash, urban and small stream flooding. However, if an organized system from the tropics were to come calling, the potential broad area of heavy rainfall produced on top of a re-saturated landscape could lead to more widespread, serious flooding.

According to Hurricane Expert Dan Kottlowski, "While there are no specific tropical systems in the Atlantic Basin at this time, August is a period in the season when there is an uptick in the number of tropical storms and hurricanes."

Instead of a zone of high pressure at most levels of the atmosphere and a northward bulge in the jet stream over the central and eastern U.S., like that of this past week, a dip in the jet stream will occur next week and beyond. (The jet stream is a river of strong winds, high in the atmosphere that guide weather systems along).

That sort of pattern tends to produce temperatures closer to normal. The flow around high pressure offshore in the Atlantic will direct moisture in from the Gulf of Mexico and the ocean over the region.

Disturbances tracking in from the Pacific Ocean will also bring a rebound of heavy, gusty thunderstorm complexes over the Plains and Midwest in the pattern.

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