Medium Range Air Quality Outlook
Mid-Atlantic Region
Issued: Sunday, July 13, 2014
Valid: July 14 – 18 2014 (Monday-Friday)

Summary:

Monday will see rain and thunderstorms in the second half of the day as a cold front approaches from the west. Cloudy skies and sustained surface flow will limit ozone to the Good range. PM2.5 will reach the Moderate due to warm air advection aloft and increased moisture. The cold front will pass through Tuesday, which will clean everything out limiting air quality to the Good range. The cold front will reach the coast on Wednesday, resulting in precipitation mainly along areas closest to the frontal boundary. Air quality will remain in the Good range. High pressure will move in overhead for Thursday and Friday. Sunny skies and calm weather will bring ozone into the Moderate range while PM2.5 will remain in the Good range for both days.

Discussion:

The weather forecast models are in good agreement for the medium range period. The beginning of the period will start with a closed low over the Great Lakes region. It will weaken and move through the Mid-Atlantic through the week. The ECMWF and the GFS start to diverge on Thursday morning when the ECMWF develops a strong shortwave over Ohio. This will affect the precipitation forecast in the northern Mid-Atlantic for Thursday and Friday.

A lee-side trough will develop on Monday, creating a chance for rain and thunderstorms for the second half of the day. Winds will pick up along with cloud cover reducing ozone to the Good range for most locations. With humidity and warm air advection aloft, PM2.5 will rise into the Moderate range for most locations.

The lee-side trough will remain on Tuesday as a cold front from the west moves through the region, keeping the high chance for rain and thunderstorms primarily in the second half of the day. Northwesterly flow aloft and cloud cover will keep air quality in the Good range for most locations.
As the cold front slowly moves through the region, Wednesday will see rain showers mainly along the coast and the southern Mid-Atlantic. The day will be mostly cloudy with northerly surface flow. Air quality will remain in the Good range.

High pressure will move in overhead as the cold front moves off the coast on Thursday, resulting in sunny skies and calm weather. Air quality will remain in the Good range yet there will be a chance for scattered Moderate ozone. High pressure will stay overhead for Friday keeping the sunny skies and calm weather. Ozone will rise into the Moderate range for most locations while PM2.5 will remain in the Good range.

-Catena