[ADEQ Forecasts] ADEQ Air Quality Forecast For Saturday, July 26, 2008

[forecasts@lists.azdeq.gov]

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

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

Health message for Friday, July 25:  Unusually sensitive people should consider reducing prolonged or heavy outdoor exertion. 

Health message for Saturday, July 26:  Unusually sensitive people should consider reducing prolonged or heavy outdoor exertion. 

Synopsis and Discussion
An interesting high ozone event occurred yesterday over parts of the Phoenix Metro area.  Numerous ozone monitors were in the mid to upper moderate range, while three monitors exceeded the 8-hour standard.  The North Phoenix and JLG Supersite monitors saw their highest 1-hour measurements of the season, shattering their previous season high by 10 and 6 ppb, respectively.  The 103 ppb hourly measurement at North Phoenix was just shy of the Valley wide season high of 104 ppb measured at Rio Verde on July 2nd.  These high hourly values were due to a prolonged period of extremely light winds during the late morning and early afternoon hours.  In fact, calm winds were reported at Sky Harbor Airport for four hours during this time period.  The situation could have been much worse, had it not been for the gusty winds that picked up during the late afternoon hours.  Ozone levels quickly dropped as these winds increased, which likely kept 8-hour concentrations below the standard at a number of sites.  Today, winds have remained moderate out of the west and as a result, ozone concentrations are some 10 - 20 ppb lower at most Central Valley monitoring sites compared to 24 hours ago.  For this reason, yesterday's Ozone Health Watch was allowed to expire.  As remnants of former Hurricane Dolly approach the state for the weekend, moisture will be on the increase, allowing for greater coverage in thunderstorms to occur over much of the forecast area.  While the greatest coverage may be confined to eastern and southeastern Arizona, the abundant moisture may produce an extended period of mid and upper level cloudiness over much of the state.  For this reason, ozone production may be held in check with AQI values likely in the mid moderate range.  As is always the case during the monsoon season, dense blowing dust can occur in the vicinity of thunderstorms due to strong winds associated with thunderstorm outflow boundaries.  Check back in on Sunday for the latest air quality updates. 
 

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