Tue Feb 17 14:35:59 MST 2009


For transportation alternatives:

Health message for Tuesday February 17: No health impacts are expected. 

Health message for Wednesday February 18: No health impacts are

Synopsis and Discussion
The strongest branch of the mid-latitude storm track has been displaced
unusually far south, and brought a weak surface cold frontal to the
local forecast area this a.m.; rainfall reports from Valley airports
indicate that accumulations were mostly <1/10".  The parent upper level
trough is forecast to weaken in place the next 24 hours, while a large
vortex develops over the Pacific.  Southwesterly flow aloft ahead of the
latter feature will build a warm ridge aloft over the western U.S. -
including Arizona - by midday Wednesday.  As a result, gradients will be
mostly weak and winds relatively light over the local forecast area thru
this forecast period.  Warming aloft (15-20 deg F in the 5-10K' layer by
Friday) and overnight inversion formation will result in modest air mass
stagnation during the morning hours during which time PM-10 (coarse) and
PM-2.5 (fine) particle levels at some locations may briefly spike;
however, no significant 24-hour average concentrations are expected.

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