[ADEQ Forecasts] ADEQ Daily Air Quality Forecast - Thursday, November 17, 2011

Wed Nov 16 12:00:23 MST 2011

Health message for Wednesday, November 16: Unusually sensitive people should consider limiting prolonged exertion outdoors.

Health message for Thursday, November 17: Unusually sensitive people should consider limiting prolonged exertion outdoors.

Synopsis and Discussion
Visibility looks pretty bad outside right now (see: phoenixvis.net).  One would think the air quality is absolutely poor, but in fact it's not (see latest pollution levels).  All pollutants are currently reading well in the Good range of the Air Quality Index (AQI).  So what's causing the reduced visibility?  Moisture.  At 10am, the temperature in Phoenix was 65°F with a dewpoint of 51°F.  That equates to a Relative Humidity of 60%.  We've discussed the phenomenon before, moisture in the air is attracted to any airborne particle, wrapping around it like chocolate syrup on an ice cream sundae. The water then acts like a prism or magnifying glass, enhancing the size and color of that particle.  Voila!  You have poor visibility due to moisture and not pollution.

The good news is that visibility will improve as the day progresses.  Heating of the surface will allow the mixing heights to increase, the inversion to break, and the air to expand, decreasing the humidity levels.  Daytime temperatures will remain in the mid to upper 70s through Friday, dropping to the low 70s Saturday and Sunday as two disturbances swing through the region.  The first will increase winds a bit on Friday and Saturday.  The second will give us our best shot of rain (though forecasted amounts are less than a tenth of an inch on Sunday).  PM10 levels may increase slightly but are expected to remain in the Good range.  PM2.5 levels may reach the lower Moderate range the next several days with limited mixing and rather cool nighttime temperatures.

Check back tomorrow for the more.  Until then, have a good day!  -J.Paul

For more information, please visit our Web page:

For transportation alternatives:

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

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

More information about the Forecasts mailing list