Saturday, July 6, 2013

Muggy and Wet Weather Thanks to Bermuda High

For the last week or so a southerly flow of air has persisted across the eastern third of the nation. This flow has pulled moisture northward from the Gulf of Mexico producing humid weather throughout the central and eastern U.S.  The moisture has also fueled showers and thunderstorms that have produced heavy rain from the Gulf Coast into the Northeast.

7-day precipitation ending the morning of July 6

The extent of the moisture on the surface is seen from the dewpoint chart from this afternoon. Dewpoint great than 65°F cover the southeastern third of the country.

Dewpoint chart for :3:00 p.m. CDT July 6, 2013

The southerly flow has been produced by two atmospheric features. One is the upper level trough that has been hanging around the central U.S. for the better part of a week and the other is a strong and persistent high pressure area called the Bermuda High. The Bermuda High is a semi-permanent, subtropical area of high pressure in the Atlantic Ocean. This feature is seasonal in nature. During the winter it ends to be located near the Azores (and is called the Azores High then). In the summer the center of this high tends to be located near Bermuda, and thus the name.

On this morning's surface map you can see this feature off the east coast. Note how the high extends well into the Midwest.

Surface map for 10:00 a.m. CDT July 6, 2013.

This morning's satellite water vapor image is once again rather striking. The center of the weakening upper trough over the central U.S. can be clearly seen over southeastern Missouri. The upper level ridge associated with the Bermuda High is easy to identify over the western Atlantic. The sinking air under the ridge suppresses cloudiness and dries the air, thus the dark and orange colors.  In between the trough and the ridge the southerly winds are funneling the moisture north from the Gulf of Mexico into the Ohio Valley.

Satellite water vapor image for 10:45 a.m. July 6, 2013

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