Wed Feb 18 13:41:34 MST 2009


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Health message for Wednesday February 18: No health impacts are

Health message for Thursday February 19: No health impacts are expected.

Synopsis and Discussion
Per local ACARS sounding data, a weak (2-3 deg C) surface-based
radiation inversion managed to form locally overnight and extended to
over 1800'.  It has since broken and dispersion today will be in the
GOOD category.  However, in the wake of Tuesday's weak frontal passage,
a ridge aloft has already begun to build over the southern half of
California; it will amplify and expand eastward over AZ during this
forecast period.  Significant warming aloft (15-20 deg F within the
5-10K' layer) is advertised to occur over the Valley by Friday morning
while surface high temps only increase by half that amount.  This, along
with stronger overnight inversion formation, will continue the trend
toward an increasingly stagnant air mass. Fortunately, northeast to
easterly gradient winds on Thursday will help to partly offset this
situation.  Several spikes in PM-10 (coarse) and PM-2.5 (fine) particle
levels occurred this morning - up to 107.2ug/m3 of the former and
23.1ug/m3 of the latter - and this is also expected to continue. In any
case, no significant 24-hour average concentrations are expected thru
this forecast period. -Reith  

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