Medium Range Air Quality Outlook
Mid-Atlantic Region

Issued: Wednesday, July 2, 2014
Valid: July 3- 7, 2014 (Thursday-Monday)

Summary:

As a cold front stalls over the Mid-Atlantic Thursday, all day rain and thunderstorms will keep air quality in the Good range. The front will make its way to the coast by Friday as T.S. Arthur travels northward to Cape Hatteras. A chance of showers before noon with partly cloudy skies will keep air quality in the Good range. High pressure will move overhead for Saturday as the cold front and T.S. Arthur move northeastward over the Atlantic, resulting in sunshine and northwesterly flow. Air quality will remain in the Good range. Sunday will continue the sunny weather with sustained winds, keeping air quality in the Good range for most locations with the exception of along the I-95 Corridor in PHL, MD, and NJ. Monday will see a rise in temperatures and dew points with partly cloudy skies. PM2.5 will remain in the Good range as ozone will reach the Moderate range primarily in the northern half of the Mid-Atlantic.

Discussion:

The weather forecast models are in close agreement for the medium range period, with the exception of the timing and location of minor shortwaves to pass through the region. The 06Z NAM, 06Z GFS, and the 00Z ECMWF agree on the approach of an upper level trough over the Great Lakes region on Thursday. The trough will pass through Friday as Arthur moves northward along the East Coast. The GFS is faster than the ECMWF and the NAM with the Arthur’s movement. If the GFS were to verify, the Arthur would converge faster with the upper level trough and leave the East Coast sooner. This would leave the northern Mid-Atlantic with drier conditions for the second half of the day for Friday. The ECMWF shows precipitation along the northeastern coast of the Mid-Atlantic due to the closer proximity of the tropical storm. Saturday-Monday will have generally zonal flow with westerly transport aloft.

A cold front will approach the western Mid-Atlantic and gradually make its way through the northern half of the region by nightfall Thursday. A pre-frontal trough will develop ahead of the frontal boundary, resulting in convection and instability. T.S. Arthur will travel northward along the coastal Carolinas by the end of the day. Widespread and potentially heavy rain and thunderstorms will last throughout the day. These conditions will keep Thursday’s air quality well in the Good range.

By Friday, the cold front will be connected to a surface low in Georgia, winding through central NC, VA, and the Delmarva Peninsula. T.S. Arthur will have made its way to Cape Hatteras by Friday morning. The cold front and the tropical storm will push off to the Atlantic through Friday night into Saturday morning. Friday will see a chance for showers before noon with afternoon showers primarily along the coast. Mostly to partly cloudy skies and northwesterly flow will keep air quality in the Good range.

As T.S. Arthur and the cold front move off the coast into the Atlantic Ocean on Saturday, high pressure will move in over the Mid-Atlantic. The day will be sunny and dry with northwesterly flow from the Great Lakes. Temperatures and dew points will return back to normal for the weekend. Good air quality is expected throughout the region.

High pressure will remain overhead for Sunday as well. The day will have clear skies and sustained winds with little to no chance of rain, resulting in Good air quality in most locations, with the exception of along the I-95 Corridor in PHL, MD, and NJ. Monday is expected to stay dry and will see a rise in temperatures and dew points as warm air is advected aloft. Partly cloudy skies and westerly transport could potentially bring PM2.5 into the Moderate range. Ozone will remain in the upper Good range most locations and will reach Moderate primarily in the northern half of the Mid-Atlantic along I-95.

-Catena/Ryan