July 15, 2010

Extreme Summer MicroClimates


Mike, when you say it's going to be 93 in Brentwood, please add at least 7 degrees.  I don't know where you live in the East Bay, but it's nowhere near Brentwood.  Today you said we would hit 93, it's 5:45 PM & 101 degrees outside.  My car & outside thermometer confirm it!!!

Marjorie Fiacco

Miss Marjorie,

You touch upon one of the bigger challenges in forecasting high temperatures during the Summer.  I receive an e-mail like yours several times during the extreme heat of our summer months when our microclimates are most visible. 

Microclimates are everywhere and can vary in size.  It's not uncommon to see a 5 - 7° temperature change over a mile or two near the coast and bay shore due to wind currents.  In our valleys and inland like Brentwood you will find more extreme microclimates based more on the type of ground you are standing on.  Air will be cooler over vegetation and warmer over concrete and, more so, over asphalt.  My own yard, which is not large, has an afternoon microclimate in the summer.  The back of my house, which faces west, is usually 10° warmer than the north side and up to 20° warmer than the front yard.   

The official high in Brentwood was 95° yesterday.  If you read the National Weather Service's guidelines for implementing weather observation equipment, you can see why such a big difference existed.

Thanks for watching.  Appreciate the feedback.

My best,




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