[ADEQ Forecasts] ADEQ Issues Air Pollution Health Watch for Wed., Apr. 8

[forecasts@lists.azdeq.gov]

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

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

Health message for Tuesday, April 7: Unusually sensitive people should
consider reducing prolonged or heavy outdoor exertion outdoors.  

Health message for Wednesday, April 8: Unusually sensitive people should
consider reducing prolonged or heavy outdoor exertion outdoors.  

Synopsis and Discussion
   The dust train continues to roll through the station as two more
disturbances are slated to impact Arizona this week.  The first will
move into the region from the west Wednesday.  Sustained winds should
increase to 15-25 mph by around 1-2 P.M.  Gusts could exceed 30 mph at
times.  Because it's now been 48 days since the last significant rain in
the Phoenix forecast area (0.06 inches at Sky Harbor on Feb. 17),
blowing dust is again likely Wednesday afternoon.  There will be a bit
of a break on Thursday, but the second wave will push through Arizona
Friday afternoon.  Similarly, wind gusts could exceed 30 mph, producing
areas of blowing dust once again.  
   The differences between this week's systems and those of the last
couple of weeks are the storm track and systems' strength.  The
disturbances on Wednesday and Friday will be coming from the Pacific
Ocean directly to the west rather than primarily over land from Alaska.
This means that we are getting closer to seeing rain as far south as the
deserts of Arizona.  In fact, Saturday morning looks to be the best
opportunity for local rain (latest models indicate almost an inch of
rain is possible Saturday morning).  Any moisture will be good to help
the suspended dust settle as well as temporarily reduce the region's
wildfire threat.  Because these systems are not as strong as last
week's, we are keeping forecasted PM-10 concentrations in the upper
"Moderate" range.  Thus, a PM-10 Health Watch is being issued for
Wednesday, April 8, 2009.
  Again, storm systems that dip this far south tend to drag ozone and
precursors across the desert floor as it approaches the Phoenix forecast
area.  The combination of these precursors and locally-generated ozone
can lead to elevated concentrations downwind of the metro area.  This
means Blue Point, Apache Junction, Tonto National Monument, Rio Verde
and Fountain Hills may see mid "Moderate" levels today through Thursday.

   Check back tomorrow for the latest on these wind events and the
impact to air quality.  Until then, have a good day! -J.Paul

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