[ADEQ Forecasts] ADEQ Issues Air Pollution Health Watch for Fri., May 15

[forecasts@lists.azdeq.gov]

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

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

Health message for Thursday, May 14: Unusually sensitive people should
consider reducing prolonged or heavy outdoor exertion outdoors. 

Health message for Friday, May 15: Unusually sensitive people should
consider reducing prolonged or heavy outdoor exertion outdoors. 
 
Synopsis and Discussion
AN OZONE HEALTH WATCH HAS BEEN ISSUED FOR FRIDAY MAY 15
The synoptic weather pattern over AZ will undergo a transformation
during the next 72 hours, and will have the potential to increase local
ozone formation and accumulation.  A low-amplitude ridge - currently
based over Mexico - will be replaced by a high-amplitude Pacific ridge
that will arrive overhead from the west by Sunday; meanwhile, a weak
upper level low will form over northern Baja.  A summer monsoon-like
flow pattern is then advertised to develop - complete with a
sub-tropical high center aloft setting up near the Four Corners - by
Sunday afternoon. Models currently agree that east to southeasterly
steering winds under this scenario would bring available moisture over
at least eastern AZ by late Saturday night.  Convective cloud buildups
may even produce gusty outflow winds and isolated areas of blowing dust
over the east Valley Sunday evening.  These same winds will tend to
suppress or even prevent the onset of the typical Valley afternoon
westerly breezes that in turn normally keep the locally-produced ozone
plume well-dispersed.  In addition, the stronger ridge means afternoon
temperatures will reach the 105-degree F mark by Saturday.  Assuming
ozone precursors (NOx & VOCs) are present in sufficient quantities,
local ozone levels are expected to approach unhealthy levels as early as
tomorrow; an Ozone Health Watch has therefore been issued.  -Reith  

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