Medium Range Air Quality Outlook
Mid-Atlantic Region

Issued: Tuesday, June 24, 2014
Valid: June 25-29, 2014 (Wednesday-Sunday)

Summary:

A cold front will move into the Mid-Atlantic region on Wednesday resulting in rain and thunderstorms for the second half of the day, limiting air quality to the Good range. A wave of low pressure will develop over NJ, along the frontal boundary, on Thursday morning. Widespread rain and thunderstorms will impact most of the Mid-Atlantic Thursday morning and continue for much of the day in the northern part of the region, resulting in Good air quality in the northern half and Moderate air quality in the southern half of the Mid-Atlantic. Friday will see a rise in ozone to the Moderate range for most locations due to mostly sunny skies and light winds as a high pressure system moves over New England, while northerly flow will limit PM2.5 to the Good range. Saturday and Sunday will be partly to mostly sunny with a chance of rain and thunderstorms. Humidity and sunshine will allow for Moderate air quality at inland locations.

Discussion:

The weather forecast models are in close agreement with the exception of Thursday night into Friday regarding the development of an upper level trough over the Northeast. This feature was hinted at in yesterday’s model runs. Today, the 12Z NAM has the most amplified upper level trough, followed by the 00Z ECMWF and then the 06Z GFS. These differences keep Friday’s precipitation forecast uncertain. The ECMWF, the GFS, and the NAM show similar predictions of an upper level trough over West Coast, a ridge over the Rockies, and a trough over the Great Lakes at the beginning of the period. Once we get to the extended forecasts, the GFS and the ECMWF show very similar paths for an upper level ridge that will develop over the Mid-Atlantic. The two models are in phase with each other for the rest of the period and into next week. They do have some differences in the timing and location of shortwaves that will impact the Mid-Atlantic for the weekend, which will affect the precipitation forecast.

Wednesday, a pre-frontal trough will develop ahead of an approaching cold font arriving from the northwest. Cloud cover and precipitation will impact the Mid-Atlantic region mainly in the second half of the day. Flow aloft will be southeasterly from the Atlantic ocean, bringing in cleaner air. Ozone and PM2.5 will be limited to the Good range for most locations.

The front will travel to the coast through Wednesday night into Thursday morning and a wave of low pressure will form over NJ. This will create widespread convection and precipitation on Thursday morning for most of the region, which will continue for much of the day primarily in the northern Mid-Atlantic. The southern half of the Mid-Atlantic will see scattered areas of Moderate ozone due to more sunshine, while the northern half will mainly have Good ozone. Southwesterly flow and persistent humidity will increase PM2.5 into the low Moderate range.

The cold front will move eastward off the coast on Friday, but will linger along the NC shore, resulting in mostly dry conditions during the day with the exception of a few scattered rain and thunderstorms. Mostly sunny skies and light winds will allow ozone to reach the Moderate range in scattered locations, whereas northerly dry flow will reduce PM2.5 to the Good range.

Saturday will see partly sunny skies with a chance for scattered rain and thunderstorms as the center of the surface Canadian high pressure system moves over MA. The high pressure will allow for northeasterly flow aloft for Saturday. The surface high pressure will extend its surface ridge down the Mid-Atlantic for Sunday, bringing mostly sunny skies, rising temperatures, and a slight chance for rain and thunderstorms. PM2.5 and ozone will be able to maintain Moderate concentrations for most locations for both days, with the exception of coastal areas, which will remain in the Good range due to the influence of onshore flow.

-Catena