[ADEQ Forecasts] ADEQ AIR QUALITY FORECAST FOR WEDNESDAY, FEBRUARY 27, 2008

[forecasts@lists.azdeq.gov]

Health message for Tuesday, Feb 26: Unusually sensitive people should
consider reducing prolonged or heavy exertion.

Health message for Wednesday, Feb 27: Unusually sensitive people should
consider reducing prolonged or heavy exertion. 

Synopsis and Discussion
Local ACARS soundings revealed the presence of a dual inversion over the
Valley this morning - one was a radiation inversion based at the surface
and the other a subsidence inversion based around 6500' with a top near
9000'.  Soundings also showed northeasterly down-slope gradient winds of
15-25 mph below the inversion aloft that managed to mix to the surface
by 10:00 a.m.  The result has been a significant but temporary
improvement in local dispersion, visibilities, and air quality.  The
gradient winds are the consequence of strong surface high pressure
building over the Great Basin in the wake of Monday's weak trough
passage.  Numerical forecasts indicate that the gradient will weaken on
Wednesday and that winds will be much lighter.  This, along with another
10+ degrees F of warming aloft by Wednesday afternoon, will set the
stage for a return to a rather stagnant air mass and an increase in
particle pollutant levels - a situation that is advertised to continue
thru at least Friday.  Even so, pollutant concentrations are not
anticipated to surpass the mid-moderate range of the Air Quality Index.
-Reith

http://www.azdeq.gov/environ/air/ozone/ensemble.pdf

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