[ADEQ Forecasts] ADEQ Daily Air Quality Forecast For Thursday, July 09, 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 Wednesday, July 08: Unusually sensitive people should consider reducing prolonged or heavy exertion outdoors. 

Health message for Thursday, July 09: Unusually sensitive people should consider reducing prolonged or heavy exertion outdoors. 

Synopsis and Discussion
Local ozone levels continue to be held far below their potential - in large part due to gusty westerly winds each afternoon.  It is no coincidence that this is occurring during the current break in the summer monsoon weather pattern, since under that regime a light or even easterly surface wind component tends to be present.  We do not expect much deviation from this pattern until Friday, by which time a strong upper level "monsoon high" is advertised to be expanding westward toward AZ.  A stretch of very hot daytime temperatures (110+ deg F) appears inevitable, but this does not necessarily mean that unhealthy ozone levels will follow.  For example, during July from 2004-2008 there were 51 days with 110+ degree temperatures at Sky Harbor Airport.  Using the current 76 parts per billion standard throughout, on only 20 days (39%) would there have been an exceedance of the 8-hour ozone standard.  The key seems to be afternoon wind speeds and whether excessive ozone accumulation can occur.  During the upcoming heat wave it appears that as the upper level high nears the Valley low-level gradients will weaken and may even assume an east to southeasterly wind component at or below the 10K' level.  Due to this prospect, the extended forecast calls for the issuance of a Health Watch or HPA as early as Friday.  This situation will be reviewed on Thursday.


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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