Medium Range Air Quality Outlook
Mid-Atlantic Region

Issued: Wednesday, June 4, 2014
Valid: June 5 – June 9, 2014 (Thursday-Monday)

Summary:

As low pressure slowly moves through the northern Mid-Atlantic region, precipitation and convection will clean out the area. Good air quality is expected for Thursday. High pressure will arrive Friday along with a clean air mass from Canada. Good air quality Friday with a slowly modifying air mass over the weekend as high pressure moves overhead. Saturday is expected to show scattered regions of Moderate air quality due to increased sunshine and light winds. Sunday and Monday will show an increase in both ozone and PM2.5 from stagnant air and increased moisture.

Discussion:

Models are in close agreement until Friday. However, on Friday, the NAM and ECMWF both show cool air arriving faster than the GFS at 850 mb. This would call for earlier ventilation of the boundary layer and cleaner air quality conditions. The GFS then shows the cooler air retreating faster than the other two models. By 18Z Saturday they generally agree that most of the cool air aloft has retreated, allowing warmer air to advect over the area. At 500 mb, the ECMWF and the GFS are quite similar in timing and location of shortwaves until they begin to diverge on Sunday morning.

A low pressure system, and its associated trough, will slowly move through the northern Mid-Atlantic Thursday. Precipitation will begin early on Thursday and clear the northern mid-Atlantic by mid-afternoon. Warm air aloft will linger over the southern mid-Atlantic along with precipitation and cloud cover. With rain and clouds likely, concentrations of both ozone and PM2.5 are expected to be in the Good range.

Friday will be a beautiful day as an upper level ridge from a high pressure system over the Great Lakes region extends over the Mid-Atlantic. A clean air mass will flow south from Quebec, which will reduce PM2.5 and ozone. There will be few to scattered clouds throughout the day and cool air aloft. The NAM persists in developing clouds along with a small disturbance running along the ridge but the other models are not in agreement on this. We suspect clouds will be limited Friday. In the southern part of the region, however, there is a chance for rain, as warm humid air will linger. This will further reduce ozone concentrations. PM2.5 and ozone will remain in the Good range for Friday.

The high pressure will move overhead Saturday. It will be clear with the exception of the southern mid-Atlantic. Northerly transport from Quebec will continue so that the incoming air mass will be clean. In addition, vertical mixing will be deep due to cool air aloft. However, winds will be near calm for most of the day Saturday. Thus, PM2.5 concentrations will be in the Good range as the air mass should not moisten and modify very quickly. Ozone will stay in the Good range for the most part with scattered regions of Moderate.

A low pressure system from the Southwest will move northward to the Great Lakes region by 12Z Sunday, bringing its attached warm front through the Mid-Atlantic. There will be a rise in dew point and temperatures and a chance for clouds and rain showers later in the afternoon. Sunday is expected to see a rise in both PM2.5 and ozone to low Moderate/high Green. By Monday, the low pressure system will move northeastward to Quebec bringing its cold front through the Mid-Atlantic. This will bring on a chance for rain showers, although it is uncertain how strong they will be. Ozone and PM2.5 concentrations could drop depending on precipitation intensity.

-Catena/Ryan