Medium Range Air Quality Outlook
Mid-Atlantic Region

Issued: Wednesday, June 11 2014
Valid: June 12 – June 16, 2014 (Thursday-Monday)

Summary:

Thursday and Friday will see a reduction in ozone and PM2.5 concentrations. There will be scattered rain and thunderstorms both days as the Canadian low moves its attached stationary front and following cold front through the Mid-Atlantic. High pressure will move into the area Saturday, with sunny conditions. A chance for afternoon rain in the southern mid-Atlantic will continue until Monday, limiting ozone to the Good range yet there will be scattered regions of Moderate ozone in the northern part. PM2.5 will stay in the Good range for the rest of the period due to the incoming dry and clean air mass.

Discussion:

The weather forecast models once again agree on the large scale phenomenon yet still disagree somewhat on the smaller scale features. The timing and location of small shortwave disturbances crossing the region Thursday still differ from model to model. The ECMWF and the GFS both agree on the location and timing of the upper level trough in Canada above the Great Lakes region until 18Z Friday. The ECMWF brings the trough further southeastward as the GFS and the NAM bring it northeastward. The ECMWF extends it southward to the top of the Mid-Atlantic on 12Z Saturday while the GFS and the NAM have it up in Canada. If the ECMWF were to verify, this would call for a greater chance of morning showers on Saturday. By 18Z of that day all three models agree on the flattening of the trough over the region. The models again diverge on Monday with timing and location of shortwaves.

The stationary front will linger over the northern Mid-Atlantic all day Thursday and will serve as a focus for scattered rain and thunderstorms throughout the region. Onshore flow from the Atlantic will also clean out the region, reducing PM2.5 concentrations to the Good range. Ozone will be limited to the Good range due to low level clouds and convection all day.

As the stationary front moves northward as a warm front on Friday, a lee-side trough will develop parallel to the I-95 Corridor ahead of the approaching cold front. Significant convection will occur along the trough creating heavy rain and thunderstorms. Air quality will be well into the Good range.
By early Saturday morning the cold front will be east of the I-95 Corridor. A region of high pressure will move overhead providing calm and sunny conditions. There is a chance for evening rain in the southern region, however, bringing cleaner conditions in VA and NC. The cold front will bring in clean dry air, which will keep PM2.5 in the Good range. Due to increased sunshine, there will be scattered regions of Moderate ozone, mainly in the northern Mid-Atlantic.

The high pressure will remain overhead for Sunday and Monday as well. However, the chance for showers and thunderstorms remains in the afternoon for the southern region. By Monday night, the models agree on region-wide rain and thunderstorms. PM2.5 will stay in the Good range for both days. Ozone, however, will depend on the timing and intensity of the storms, but it is expected to reach the Moderate range.

-Catena/Ryan