[ADEQ Forecasts] ADEQ AIR QUALITY FORECAST FOR FRIDAY, MARCH 13, 2009

[forecasts@lists.azdeq.gov]

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

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

Health message for Thursday, March 12, 2009: Unusually sensitive people should consider limiting prolonged or heavy exertion outdoors. 

Health message for Friday, March 13, 2009: No health impacts are expected. 
	
Synopsis and Discussion
  The breezy conditions are just not panning out as yesterday's forecast models suggested.  It is still early, but a couple things may keep those winds from being realized here in the Phoenix forecast area Thursday afternoon.  The first is that the center of the low is passing to the south of Arizona.  This means that the stronger winds from the west are occurring in Mexico.  The second factor is that the winds in the upper levels are just on translating down to the surface.  The lack of significant surface winds and increased atmospheric humidity mean that PM-10 concentrations may not climb as high as expected on Thursday.  
   By Friday, a rather strong ridge of high pressure will begin to build back over the region.  Afternoon desert temperatures could reach the upper 80s to near 90°F by next Tuesday and Wednesday under mostly sunny skies and relatively light winds.  These conditions are favorable for ozone generation.  Adding to that is the possibility of a weak transport scenario.  This means that the weather pattern will set up with the general flow from the central valleys of California southeast through southern California and then east towards Phoenix.  Such a pattern often promotes transport of ozone and/or precursors into Phoenix from the deserts west of the forecast area.  This addition ozone source combined with locally-generated ozone could result in our first "Moderate" levels of the year, possibly as early as Saturday.  The pattern will remain in place through much of next week.  Check back tomorrow for more detailed look at the weekend.  Until then, have a good day!  -J.Paul

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