[ADEQ Forecasts] ADEQ AIR QUALITY FORECAST FOR SATURDAY, APRIL 13, 2009

[forecasts@lists.azdeq.gov]

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

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

Health message for Friday, April 17: Unusually sensitive people should consider reducing prolonged or heavy outdoor exertion outdoors.  

Health message for Saturday, April 18: Unusually sensitive people should consider reducing prolonged or heavy outdoor exertion outdoors.  

Synopsis and Discussion
   High pressure will begin to build strong over the forecast area this weekend.  Mostly sunny skies and relatively light winds will be the result.  Following a high of just 68°F Thursday in Phoenix, temperatures will soar to possibly the first 100 degree day of the year Tuesday!  This will also allow mixing heights to increase to more that 7,000 feet which will allow ample room for low-level pollution dispersion.  Unfortunately, ozone levels will be elevated this weekend.  The position of the high will cause the flow to be out of the northeast on Sunday and Monday, fairly similar to what we see during the monsoon season here in Arizona.  The difference is that there will be no moisture.  Typically we see ozone concentrations significantly increase with the shift in winds from west to east.  The sustained east to west flow tends to keep the locally generated ozone trapped in the metropolitan area without being able to disperse to the east.  This means that sites like North Phoenix, Central Phoenix, Cave Creek, Pinnacle Peak, and Fountain Hills may see ozone concentrations climb into the upper "Moderate" range on Sunday and Monday.  Winds should return to a more normal southwest to northeast flow by the middle of next week, allowing ozone levels to drop off a bit.  Otherwise, it should be a decent weekend for some early morning and late evening activities.  Check back Sunday for the latest.  Until then, have a great weekend!  -J.Paul

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