[ADEQ Forecasts] ADEQ AIR QUALITY FORECAST FOR FRIDAY, FEBRUARY 20, 2009

[forecasts@lists.azdeq.gov]

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

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

Health message for Thursday February 19: No health impacts are expected.


Health message for Friday February 20: Unusually sensitive people should
consider reducing prolonged or heavy exertion. 

Synopsis and Discussion
Per local ACARS sounding data a rather stagnant morning was underway
over the Valley this a.m. courtesy of a moderate (4-5 deg C)
surface-based radiation inversion that formed overnight. However, the
same data indicates that the best mixing depth today will be in excess
of 6K' and that dispersion will be in the FAIR to GOOD category range.
With a ridge aloft gradually building overhead, and additional warming
aloft yet to occur - 7-14 deg F in the 5-10K' layer by Friday afternoon
- stagnant mornings will be a fixture thru the upcoming weekend.
Despite a pair of elevated hourly particle pollutant readings this
morning - 270.4ug/m3 of PM-10 at the West Forty Third site and 29.4ug/m3
of PM-2.5 at West Phoenix - daily averages are still not expected to
exceed the low-moderate range of the Air Quality Index thru this
forecast period.  Since afternoon temperatures are forecast to approach
80 degrees F by Sunday and winds are advertised to be light, ozone
production should jump a bit.  Other factors favoring increasing ozone
levels are that since the Winter Solstice the local day-length has
increased by 75 minutes and the noon sun-angle has risen by nearly 13
degrees.  Even so, this is a far cry from the 80-degree sun-angle
experienced on the Summer Solstice.  Since 2004 the first AQI moderate
range ozone day has varied from as early as March 10 in 2007 to as late
as April 02 in 2005.  Although the official start of the local ozone
season is still forty days away, it is not too early to begin watching
its evolution. -Reith  

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