[ADEQ Forecasts] ADEQ Daily Air Quality Forecast for Friday, July 31, 2009

[forecasts@lists.azdeq.gov]

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

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


Health message for Thursday, July 30: Unusually sensitive people should consider limiting prolonged or heavy exertion outdoors.

Health message for Friday, July 31: Unusually sensitive people should consider limiting prolonged or heavy exertion outdoors.


Synopsis and Discussion

Models are in agreement that the Monsoon high will slide east the next few days from its current position over Baja.  This would put it over central New Mexico by Saturday, shifting the Arizona's upper-level winds from the dry southwesterly direction to a moist southeasterly flow.  Any thunderstorm activity today and Friday will be confined to the Four Corners region as well as southeastern Arizona with storm movement to the east.  Saturday's shift will steer any storms in southeastern Arizona towards the northwest.  Chances of rain here in the Phoenix forecast area will remain slim this weekend, but outflow-generated dust could possibly impact the Valley.  The best chances for pollution-clearing rain in Phoenix will be on Monday and Tuesday where the potential for short waves rotating clockwise around the Monsoon high could enhance thunderstorm development and sustain them through the overnight hours.  Otherwise, afternoon desert temperatures will continue to be 5-10 degrees above normal for this time of year under mostly sunny skies.

The current southwesterly flow has been largely beneficial in dispersing the invisible ozone plume to the northeast the past several days, resulting in all sites staying in the "Good" range on Wednesday.  The abrupt shift in winds on Saturday, however, will do more than draw much need moisture from Mexico into the region.  It will also block locally-generated ozone and precursors from exiting the Valley to the northeast.  This would cause the ozone to pool closer to the center of Phoenix with concentrations possibly nearing the health standard in the central and north parts of the Valley.  Thus a Health Watch may be necessary on Saturday.  Tomorrow we should have a better idea on the timing of high pressure movement and associate wind shift, so check back then for the latest.  Have a good day!

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

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


 

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