Wednesday, July 17, 2013

This Heat Dome Is Not A Bermuda High

We wanted to share with you a couple of graphics that show the difference between a "typical" Bermuda High that sets up shop in the western Atlantic and the high pressure ridge that's built overhead and is slowly nudging west the past couple of days.

The first image shows the current heat dome based on its position over Michigan and Ohio on Monday night. This high is impressive for any location in the Northern Hemisphere, with a "height" of 600 dm (more than 19,680' in the atmosphere) registered for the 500mb air pressure "line" in the atmosphere.  This yields some serious ridging of air in the atmosphere and an anomalously strong ridge of high pressure for anyplace.  What is helping us heat up is the position of this ridge of high pressure.  Typically, summer ridges in the Ohio Valley and eastern parts of the Corn Belt are the most ideal location as we can benefit from a "drying" effect of westerly surface winds that dry out and heat up downstream from the Appalachians.




In past "classic" heat waves from 2010, 2011, and even 2012 the position of the heat ridge was pretty similar -- Great Lakes, Ohio Valley, Corn Belt...some variant of the three.  We probably won't hit 100 in this heat wave, unlike those from the last three years, thanks to all that rain we got in June and the first week of July.  Had we gone into this heat wave with a bit less moisture in the soil, we probably would have a run at 100 in the offing for this heat wave.

A Bermuda High sets up in the western Atlantic, typically near Bermuda. When it flexes west, the high pressure ridge influences the East Coast with warmth...but also humidity. Typically, a Bermuda High is positioned farther east and southeast, more consistently positioned in the Atlantic.



Notice the geographic difference between a "classic" Bermuda High and the ridge that's to our west.  More important, this was never a Bermuda High to begin with...it developed over New England in response to the upper level disturbance that impacted us on Friday with rain.  As that upper level low slide slowly west and southwest, an upper level high built overhead and increased in intensity. Bermuda Highs don't originate in New England!

Summer can feature high pressure ridges of varying sorts and intensity -- and this heat dome is no exception.  However, it isn't a Bermuda High in size nor position nor origin...but it has produced a rather summery run of heat.