[ADEQ Forecasts] ADEQ Daily Air Quality Forecast for Thursday, July 30, 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 29: Unusually sensitive people should consider limiting prolonged or heavy exertion outdoors.

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


Synopsis and Discussion

A stiff southwesterly flow persists across the region due to the current position of the upper level high pressure system.  This flow continues to shut off the moisture source from Mexico which drives our summertime Monsoon thunderstorms this time of year.  At the same time, the ridge has finally expanded north along the west coast all the way into Canada and Alaska.  Some spots in Washington and Oregon are expected to top 100°F Wednesday through Friday.  With the help of a cut-off area of low pressure off the coast of California, our high will slowly push northeast through the weekend, setting up shop over central New Mexico.  This will resume the typical moisture pull from Mexico northward into Arizona by early next week.  It will take a couple days after that to get back into a solid thunderstorm pattern.

In the meantime, the relatively dry southwesterly flow continues to push the locally generated ozone plume to the east and northeast.  This will be the case on Wednesday and Thursday.  As the high slides east, the flow will become more southerly, pushing the plume to the north part of the Valley.  This means that sites such as Fountain Hills, Tonto National Monument, Pinnacle Peak and Rio Verde will likely be the recipients of the highest ozone concentrations on Wednesday and Thursday, and North Phoenix, Cave Creek and Pinnacle will be the target areas on Friday.  (Follow up to yesterday's discussion: it doesn't appear that we will get much import from southern California as the high is pushing much of their ozone northeast into Las Vegas)

The last significant rainfall (0.36 inches at PHX-Sky Harbor) was 8 days ago.  Aided by the drier southwesterly flow, the surface moisture has quickly evaporated, allowing local dirt and dust to become more readily suspended in the lower atmosphere.  Fortunately, rapid morning surface heating and maximum afternoon mixing heights around 10,000-12,000 feet allow the Particulates to mix out.  Otherwise we would be looking at 24-hr PM-10 concentrations much higher than the low "Moderate" readings we've seen the past couple of days.  These levels will continue through Friday, decreasing slightly as increased moisture over the weekend will help weigh the particles down. 

Check back tomorrow for the latest. Until then, have a good day!

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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