Forecast Discussion:
High pressure will pass by to our west during the weekend with onshore winds and rain likely by Monday. For Saturday, light westerly winds and mostly sunny skies. PM concentrations are rising upwind (west) today and this will be sufficient to raise local PM levels to just within the moderate range Saturday.

Extended Forecast:
Winds will slowly veer to the northeast on Sunday with increasing clouds. Increasing humidity and a good chance of fog in the morning hours will help keep PM in the low moderate range. As low pressure moves to near Cape Hatteras on Monday, we will see increasing onshore winds and rain. The strength of the winds, and onshore direction, will drop air quality back to the good range. To follow air quality in PHL between forecasts: "aqforecast" at www.twitter.com -Ryan