Phoenix weather: Changes in store this weekend; Ozone Health Watch today

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PHOENIX -- Strong high pressure building over the Southwest means a couple more very warm days across the Valley. Above-average temperatures, peaking in the upper 80s today and tomorrow, will be accompanied by abundant sunshine.

Our warmest day of the week will likely be Saturday, when we could see our first 90-degree day of the year. The heat will subside with the approach of a low-pressure system on Sunday. It looks the the storm will keep its rain and snow well to our north, but look for increased winds and clouds, along with cooler temperatures on Sunday. 

We're forecasting a high of 77 on Sunday and just 79 on Monday.

The mid 80s are forecast to return by the middle of next week. 

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The Arizona Department of Environmental Quality has issued an Ozone Health Watch for the Valley today -- our first of 2012 -- for ozone levels that are expected to approach unhealthy levels. Residents are encouraged to carpool, limit driving, avoid using gas-powered equipment and refuel after dark.

Ground level ozone is an invisible gas created when other pollutants in the air -- such as those created by combustion (like in car engines) -- are heated by the sun.

Authorities say ozone can aggravate existing respiratory conditions such as asthma.

People with these conditions as well as the elderly and very young should avoid time outdoors, especially during the early evening hours when ozone production can peak.

The Valley of the Sun has a longer than average "ozone season," running from April to September.