First Real Heat Wave of the Summer

Tuesday was the fourth day in what is going to be about a nine day stretch above 90 degrees.  The longest stretch that we’ve ever seen with temperatures in the 90s, in September, was eight days back in 1974.  That only happened one other time in 1944.  So if this 9 day stretch in the 90s pans out, we would experience something that has never been recorded in Eugene.

A big ridge of high pressure has set up shop over the Pacific Northwest.  High pressure sets up a sinking atmosphere, where the air descends from the upper levels of the atmosphere to the surface.  This process prohibits clouds from forming and gives us the clear blue sky.  High pressure also compresses the air, which heats it up.  So all the physics are in place to keep the mercury above 90.

500

*The photo to the above is geopotential hight at 500mb, which shows the deep trough to the west and high ridge over the Pacifc Northwest.

Now the reason that this high pressure area is so stationary, is because of two deep areas of low pressure – one to west and one to east.  Although this particular one isn’t well developed, the formation as seen on the 500 mb chart sets up what is known as an omega high.

These three systems are all feeding into each other…prohibiting them from moving on, making this a long heat wave for us in the Pacific Northwest.

With high pressure at its peak, today will be the hottest day of the week and so far in 2011.  A Heat Advisory is in effect from 11 a.m. to 11 p.m.  Temperatures will be between 95 and 100 degrees during the afternoon and early evening hours.  To break a record, we’ll have to get above 98 degrees in Eugene.

The elderly and those without access to air conditioning will be particularly vulnerable.  Take precautions if you work or spend time outside. The Occupational Safety and Health Administration recommends scheduling frequent rest breaks in shaded or air conditioned environments to reduce the risk of heat stroke.

Stay cool,

Meteorologist Melissa Frey

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