[ADEQ Forecasts] ADEQ Daily Air Quality Forecast for Wednesday, August 12, 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 Tuesday, August 11: Unusually sensitive people should consider limiting prolonged or heavy exertion outdoors.

Health message for Wednesday, August 12: Unusually sensitive people should consider limiting prolonged or heavy exertion outdoors.

Synopsis and Discussion
Confidence is pretty low concerning rain in the Phoenix forecast area the next couple of days.  Yes, high pressure has returned to a more favorable position just south of the Four Corners area, and yes, moisture will be increasing from the south each day through the end of the week.  However, models are predicting that most of the storms will stay to the south and east of the Valley.  The best chance to get a storm to roll into the forecast area will be Thursday night into early Friday as they will light up to our south, east and northeast.  Steering winds could drive a couple cells off the higher elevations and into the lower deserts.  Afternoon desert temperatures around 105-108°F with surface dew points in the low to mid 60s could be enough to sustain a strong thunderstorm right over the Valley on Thursday.  Otherwise, we're looking to dry out once again over the weekend as yet another trough of low pressure drags its way across the western U.S.

Ozone concentrations showed some life on Monday, reaching the mid to upper "Moderate" range at several sites, the highest levels being recorded at South Scottsdale (80 AQI).  East and southeasterly flow up to 18,000 feet could trap surface ozone and precursors in the Valley leading to concentrations in the upper "Moderate" range by Thursday.  A little bit of shear-enhance vertical mixing might be enough to keep levels from exceeding the standard.  However, if conditions fall into line at 850 millibars (approx. 5,000 ft), then we could be looking at several Valley exceedances on Thursday.  We'll know a bit more tomorrow.
Particulates were up a bit with West 43rd reaching the low "Moderate" range (52 AQI).  Increased moisture has amplified the appearance of suspended particles, making it look worse than it actually is Tuesday morning.  Visibility will improve as the mixing heights increase throughout the day.  There is an increasing possibility of blowing dust from distant thunderstorms that could impact our local air quality then next few days, resulting in higher PM-10 and PM-2.5 concentrations.  Otherwise, local PM-10 and PM-2.5 concentrations will mainly be in the upper "Good" to low "Moderate" range.  Check back tomorrow for the latest.  Until then, 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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