[ADEQ Forecasts] ADEQ AIR QUALITY FORECAST FOR THURSDAY, APRIL 16, 2009

[forecasts@lists.azdeq.gov]

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

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

Health message for Wednesday, April 15: Unusually sensitive people
should consider reducing prolonged or heavy outdoor exertion outdoors.  
Health message for Thursday, April 16: Unusually sensitive people should
consider reducing prolonged or heavy outdoor exertion outdoors. 
 
Synopsis and Discussion
A PM-10 HEALTH WATCH REMAINS IN EFFECT THRU MIDNIGHT
Over the past 18 hours a large and cold upper level trough in the
mid-latitude storm track has descended upon the western third of the
U.S. and an associated dry cold front passed over the Valley proper
around 9:00 a.m. this morning.  Low-level gradient winds will remain
strong over the metro area thru midday (up to 58 mph at the 10K' level)
and another windy day is already underway.  Although some blowing dust
was reported Tuesday afternoon, the highest hourly PM-10 (coarse
particle) level was only 208ug/m3 at the West Forty Third site at 6:00
p.m., and concentrations dropped off significantly thereafter.  Higher
hourly PM-10 concentrations have already occurred today (240.9ug/m3 at
West Forty Third at 8:00 a.m.) and at 10:00 a.m. remain elevated above
100ug/m3 at four monitoring sites - from 102.6 ug/m3 at South Phoenix to
128.4ug/m3 at West Forty Third; thus, the PM-10 Health Watch will remain
in effect thru midnight.  Winds in the 5-10K' layer will be conducive to
ozone & precursor transport from California by later this afternoon, so
a modest jump in local ozone levels may occur overnight and continue on
Thursday.  The extant storm system will be slow to move east the next 48
hours, but by Saturday a massive upper level ridge will begin building
over Arizona from the west.  Its possible impacts on future Valley ozone
production/levels will be addressed in tomorrow's discussion.  -Reith   

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