[ADEQ Forecasts] ADEQ AIR QUALITY FORECAST FOR THURSDAY, MARCH 19, 2009

[forecasts@lists.azdeq.gov]

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

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

Health message for Wednesday March 18: Unusually sensitive people should
consider reducing prolonged or heavy exertion outdoors.  

Health message for Thursday March 19: Unusually sensitive people should
consider reducing prolonged or heavy exertion outdoors. 

Synopsis and Discussion
Local morning ACARS sounding data indicates that a moderate (6-7 deg C)
surface-based radiation inversion formed overnight and that it reaches
to near 1900'.  This afternoon's mixing depth is calculated to be near
8800' but the mean wind speed thru this layer is only around 5 mph.
Thus, although stagnation of the Valley air mass will decrease with
time, ultimate dispersion will only be in the FAIR category.  The
inversion has undoubtedly contributed to some rather high hourly coarse
particle (PM-10) levels at a number of monitoring sites this a.m.  Some
of these readings include 79.1ug/m3 at Buckeye, 80.8ug/m3 at South
Phoenix, 126.5ug/m3 at Higley, and at West Forty Third concentrations
ranged from 137.2-278.7ug/m3 between 5:00 and 8:00 a.m.  Meanwhile,
ozone levels have risen about as expected but mostly at outlying
locations; considerable high clouds on Thursday may keep ozone
production below its potential.  The warm upper level ridge that has
been over the local forecast area the past few days will amplify on
Thursday as a weak trough approaches from the west.  This trough will
eventually dissipate within the large-scale flow pattern as a large and
intense disturbance approaches from off the west coast.  Looking ahead,
winds will increase by Saturday afternoon ahead of an associated strong
surface cold front and a windy & dusty day is possible on Sunday; the
issuance of at least a PM-10 Health Watch may be needed. 
-Reith  

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