[ADEQ Forecasts] ADEQ AIR QUALITY FORECAST FOR SATURDAY, APRIL 26, 2008

[forecasts@lists.azdeq.gov]

http://www.azdeq.gov/environ/air/ozone/ensemble.pdf

Health message for Friday, Apr 25:  Unusually sensitive people should consider reducing prolonged or heavy exertion outdoors. 
 
Health message for Saturday, Apr 26:  Unusually sensitive people should consider reducing prolonged or heavy exertion outdoors. 
 
Synopsis and Discussion
For the third time this week, the Phoenix forecast area saw ozone concentrations exceed the new federal health standard.  And it's only April!  Under the old standard, Tonto National Monument (the site of yesterday's exceedance) would have only been in the mid-"moderate" category.  The latest health studies support the new standard, so it will still go down as an exceedance.  Today is a new day, however, and with that we expect ozone concentrations to be lower across the board thanks to a decrease in transport from the west.  It hasn't completely shut down, but the direction and speed of the incoming air mass has changed enough that the Valley is no longer the direct target of ozone transport.  High pressure will build over the region this weekend into early next week, producing significant heat.  Many desert locations will see their first triple digit temperatures of the year.  Phoenix is expected to reach the upper 90s to around 100°F on Monday and Tuesday.  With increased surface heating, typical afternoon breezes due to the Valley's diurnal wind pattern will take affect.  As a result, the high ozone levels will likely be in the far east Valley this weekend (Apache Junction, Fountain Hills, Tonto N.M, etc.).  Increased mixing heights and better ventilation will allow Particulates drop off as well.  We are now on day 60 without measurable rain and counting, so it won't take much for those levels to rise again.  Check back on Sunday for a closer look at your coming workweek.  Have a great weekend!  -J.Paul

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

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