Medium Range Air Quality Outlook
Mid-Atlantic Region

Issued: Saturday, June 14, 2014
Valid: June 15 – June 19, 2014 (Sunday-Thursday)

Summary:

Sunny and warm weather for Sunday and Monday as high pressure remains overhead. Northerly flow from Canada will keep PM2.5 in the Good range along with scattered regions of Moderate ozone for Sunday. With increasing humidity, sunshine, and a more stagnant atmosphere, air quality will reach the Moderate range for Monday. As a pre-frontal trough develops Tuesday morning and lingers for the rest of the period until Thursday, there is a daily chance for scattered rain and thunderstorms. Westerly flow and little mixing will keep air quality in the Moderate range for all three days, yet ozone could possibly reach Code Orange depending on the timing and arrival of storms and cloud cover.

Discussion:

The weather forecast models are in good agreement on the large-scale phenomenon but mostly disagree on the small mesoscale features after Monday. They strongly agree to sunny weather until Monday night when they start to diverge from one another. They also agree on warm air transport aloft starting Monday morning, lasting until the rest of the period. This will create a stable atmosphere allowing ozone and PM2.5 to easily accumulate.

The models have come in slightly better agreement for the upper air forecast for Tuesday. Zonal flow aloft will last for most of the day as an upper level ridge builds up to the west of the Mid-Atlantic. The GFS, however, develops a more pronounced trough over the Northeast U.S. starting early Tuesday, suggesting that small mesoscale disturbances will travel further south than predicted. The medium range models disagree on the timing and location of MCS’s to hit the area Tuesday through Thursday, however, creating a chance for precipitation and cloud cover each day, which could limit ozone accumulation.

Sunday will be warm and sunny with high pressure overhead. Northerly Canadian transport will keep the day dry and clean with a high atmospheric boundary layer. PM2.5 will stay in the Good range while scattered regions of Moderate ozone will develop throughout the Mid-Atlantic from cloudless skies.

High pressure will remain overhead for Monday with northerly flow transitioning to southwesterly recirculation from VA by the evening. Transport of warm air aloft will result in a stagnant atmosphere with light winds and little mixing. PM2.5 will reach the Moderate range along with ozone due to increased sunshine.

By Tuesday, a pre-frontal trough will develop down the Mid-Atlantic ahead of an approaching cold front. There will be a chance of showers and thunderstorms throughout the day with westerly flow from the Ohio River Valley. Tuesday will be hot and humid as temperatures and dew points will rise to above normal. Air quality will remain in the high Moderate range for Tuesday, although there is a chance for ozone to reach the USG range depending on precipitation and cloud cover.

The pre-frontal trough will linger over the Mid-Atlantic for Wednesday and Thursday. By 12Z Thursday, the cold front will move to northern PA. As stated above, there is still uncertainty in the timing and location of rain and thunderstorms to hit the region for both days. PM2.5 will stay in the Moderate range while ozone could reach the USG range depending on the intensity of the storms and when they arrive, mostly sunny skies, westerly flow from the Ohio River Valley, and light winds.

-Catena/Ryan