Wed Jan 21 12:33:46 MST 2009


For transportation alternatives:

Health message for Wednesday January 21: Unusually sensitive people
should consider reducing prolonged or heavy exertion. 

Health message for Thursday January 22: No health impacts are expected. 

Synopsis and Discussion
A rather stagnant air mass continues to impact the local forecast area
this today but improvements are on the way.  Overnight inversion
formation, less-then-favorable dispersion, and considerable cloud cover
contributed to some locally high spikes in particle pollution this a.m.
Highest hourly coarse particle (PM-10) levels reached 183.7ug/m3 at the
West Forty Third monitoring site, 205.4ug/m3 at Durango, 166.5ug/m3 at
West Phoenix, and 149.2ug/m3 at Higley.  The single highest fine
particle (PM-2.5) concentration was 38.6ug/m3 at West Phoenix.  The
strong upper level ridge that has been over the state so far this week
will move east today and be replaced by a weakening trough in the
southern branch of the mid-latitude storm track.  Although Valley
rainfall totals with this system are expected to be rather light, any
amount will help to re-stabilize disturbed soils that have contributed
to rising PM-10 levels the past few days.  Increasing mixing depths and
prevailing breezes will also help to improve local air mass ventilation
the next few days with mostly good air quality predicted for Thursday
and Friday.  -Reith  

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