[ADEQ Forecasts] ADEQ AIR QUALITY FORECAST FOR WEDNESDAY, MAY 13, 2009

[forecasts@lists.azdeq.gov]

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

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

Health message for Tuesday, May 12: Unusually sensitive people should
consider reducing prolonged or heavy outdoor exertion outdoors. 

Health message for Wednesday, May 13: Unusually sensitive people should
consider reducing prolonged or heavy outdoor exertion outdoors. 
 
Synopsis and Discussion
Local ozone concentrations were rather low over the weekend, and hourly
readings as of 10:00 a.m. this morning were in the 37-47 parts per
billion range - at or slightly below those of 24 hours ago.  For the
first 11 days of May in 2008 the Valley maximum AQI level for ozone
averaged 83, while this month it is only 69; a look at archived data
indicates that ozone levels upstream in CA have also been considerably
lower than this time last year.  It is too early to tell if this trend
will continue; however, the potential for an increased influx of ozone
and its precursors from CA the next 24 hours has led to a local forecast
AQI level just below Health Watch criteria for Wednesday.  Looking
ahead, weakening low-level gradients on Friday followed by a shift to a
low-grade easterly wind regime over the weekend means that ozone
accumulations will likely be on the rise.  As a result, the extended
outlook calls for an increased risk for a sequence of days with
near-to-unhealthy ozone levels. -Reith   

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