[ADEQ Forecasts] ADEQ Extends Today's Ozone Health Watch for the Phoenix Metro Area through Wednesday, May 09, 2012

[forecasts@lists.azdeq.gov]

Health message for Tuesday May 08: Unusually sensitive people should consider reducing prolonged or heavy exertion outdoors.

Health message for Wednesday May 09: Unusually sensitive people should consider reducing prolonged or heavy exertion outdoors. 

Synopsis and Discussion
*TODAY'S AN OZONE HEALTH WATCH HAS BEEN EXTENDED THRU WEDNESDAY MAY 09*
OZONE:  A weak upper level low in the southern branch of the mid-latitude storm track is currently located near Yuma and is forecast to migrate west to east over northern Mexico during the next 48 hours.  Per the most recent Sky Harbor ACARS sounding data, winds at and above the 5K' level over the Valley have already become northeast to easterly due to the cyclonic (counter-clockwise) circulation around this feature. This type of wind regime often accompanies/contributes to local high ozone levels by inhibiting dispersion of the ozone plume.  An even more pronounced easterly wind regime is forecast for Wednesday - in fact, surface winds will likely start out rather gusty with good ozone dispersion but then decrease or become light during the afternoon.  In addition, persistent cloud cover may inhibit ozone formation and outflow winds from distant thunderstorms during the late afternoon and evening could also intervene.  However, there is enough uncertainty at this point to argue for a continuation of today's Ozone Health Watch thru tomorrow.  There are signs that some transport of additional ozone and/or its precursors from the west will begin on Thursday so additional health statements are possible.  

PARTICLES:  The weather pattern described above is forecast to draw enough moisture over Arizona by Wednesday to produce a few thunderstorms over the higher terrain east and southeast of the Phoenix metro area.  For the Valley this means the potential for strong and gusty outflow winds and an increased risk for dense blowing dust - mainly over the east and southeast portions.  Thus higher PM-10 (coarse particle) levels are possible on Wednesday.   


For more information, please visit our Web page:
www.azdeq.gov/environ/air/ozone/ensemble.pdf 

For transportation alternatives:
www.valleymetro.org 


If you have any questions or comments regarding this forecast please contact:

Mark Shaffer, Communications Director
Arizona Department of Environmental Quality
Office of Communications
1110 W. Washington St., Phoenix, AZ 85007
(602) 771-2215
ms15@azdeq.gov