[ADEQ Forecasts] ADEQ AIR QUALITY FORECAST FOR WEDNESDAY, MAY 20, 200

[forecasts@lists.azdeq.gov]

http://www.azdeq.gov/ensemble.pdf

For transportation alternatives:
http://www.valleymetro.org

Health message for Tuesday, May 19: Unusually Sensitive People should consider limiting prolonged or heavy exertion outdoors.  

Health message for Wednesday, May 20: Unusually Sensitive People should consider limiting prolonged or heavy exertion outdoors.  

Synopsis and Discussion
   What an exiting couple of days weather-wise it has been with the monsoon-like moisture and thunderstorms.  Though there wasn't a whole lot of rain that fell across the Valley (general accumulations if any were around 0.04 inches), the lightning shows were great to watch.  High pressure currently located near the Four Corners region, has drawn a good fetch of subtropical moisture into the region.  The above normal heat we've been experiencing (one degree shy of the record 107°F in PHX on Monday) has been the fuel needed to form the strong storms along the Rim.  We should see more of the same the next few days with Thursday night into early Friday being the best chance of seeing some measurable rain here in the Valley of the Sun.  As the high continues to slide east, we will see a return to a much drier, southwesterly flow by the weekend. 
   Air quality-wise, the easterly flow around the south side of the high pressure system has been locking ozone and precursors in the Valley, preventing them from naturally escaping to the east.  As a result, we saw 4 in-town exceedances of the 8-hr Ozone health standard on Sunday, several near exceedances on Monday, and we may see a few more elevated readings today.  Fortunately, overnight and early morning debris clouds combined with a wind pattern shift back to a more southwesterly flow should help disperse some of this accumulated ozone.  Thus, Wednesday through Friday should see lower ozone concentrations in the Phoenix forecast area.  Outflow from thunderstorms may generate some periods of blowing dust during the evening hours.  Thus, particulate concentrations may reach "Moderate" levels the next few as well.  Check back tomorrow for more.  Until then, have a good day.  -J.Paul

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