Medium Range Air Quality Outlook
Mid-Atlantic Region

Issued: Sunday, August 2, 2015
Valid: August 3-7, 2015 (Monday – Friday)

Summary:

An upper level low moving slowly across southern Canada will spawn a series of weak frontal boundaries that will cross the mid-Atlantic during the week. Warm weather and mostly sunny skies will keep ozone in the Moderate range. Particle concentrations will move up and down as humidity and ventilation varies day to day but will be generally in the low Moderate range.

Discussion:

The forecast models (NAM, GFS and ECMWF) remain internally consistent and in good agreement with each other through the medium range resulting in high confidence in the weather and air quality forecasts. In the large scale flow, a closed upper level low just west of James Bay will drift to the east, reaching QC by Wednesday. Zonal flow will then set up for the remainder of the period with another deep trough forming to our west late Friday. At the surface, this pattern will be associated with a series of weak frontal boundaries moving through the mid-Atlantic. This will prevent any significant build-up of pollutants although sunny skies and humid air will keep air quality in the Moderate range for the bulk of the coming work week.

On Monday it will be warm, sunny and humid with strong southwest winds. Deep vertical mixing and steady winds will keep air quality in the Moderate range with highest concentrations along the I-95 Corridor.

The forecast models have slowed the approach of the first in a series of cold fronts and we now expect the front to reach the I-95 Corridor during the Tuesday morning rush hour. There will be significant convection west of the mid-Atlantic late Monday into the nighttime hours. For Tuesday, there is slight change of rain in the mid-Atlantic. Winds will shift west and remain strong while deep vertical mixing is again expected. Air quality will be at the Good/Moderate threshold with highest concentrations east of I-95.

A change in air mass will lag the frontal passage with drier air finally filtering in late Tuesday.   The next weak cold front is expected during the day Wednesday. Air quality remains in the Good to low Moderate range. Humidity returns Thursday with one more frontal passage Friday. Moderate air quality is expected both Thursday and Friday.

-Ryan