Medium Range Air Quality Outlook
Mid-Atlantic Region

Issued: Friday, June 26, 2015
Valid: June 27- July 1, 2015 (Saturday – Wednesday)

Summary:

Air quality will stay within the Good range throughout the medium range period as a series of surface waves and frontal boundaries make their way through the region. Most notably, inches of rain are expected across the northern and central Mid-Atlantic over the next 48 hours, making for a very clean atmosphere by the time skies clear on Monday. Tuesday and Wednesday will continue to see mostly cloudy skies and scattered showers as weak frontal boundaries move through the region.

Discussion:

The weather models are in close agreement on the overall synoptic features throughout the medium range period. The 06Z NAM, 06Z GFS, and 00Z ECMWF were consulted for this analysis. By Saturday morning, the anticipated longwave trough in the eastern US will take shape, with its base reaching down to the Gulf of Mexico. Shortwaves over the Tennessee River Valley (TRV) will form a wave of low pressure on Saturday. These shortwaves will be become organized and form a closed low at 500 mb Saturday afternoon. As the wave of low pressure moves northeastward, it will bring widespread clouds and precipitation to the area. The heaviest rain will likely be in the northern Mid-Atlantic (NMA) where the closed 500 mb low will be located. This closed low will slowly move northeastward and open up Sunday night into Monday morning. On Monday, a series of disorganized shortwaves will drop down from western ON and reinforce the longwave trough. This feature will pull another cold front eastward from the Ohio River Valley (ORV). The upper level flow will prevent this cold front from reaching into the Mid-Atlantic. Pieces of the shortwave energy will move over the Mid-Atlantic on Tuesday as the longwave trough will begin to weaken. Another series of shortwaves will drop down from ON into the Great Lakes and rotate around the base of the weakening trough. These shortwaves will help pull another cold front into the Mid-Atlantic on Wednesday.
A large surface wave currently approaching from the southwest will bring widespread clouds and steady rain to the entire Mid-Atlantic tomorrow, as well as breezy, onshore winds. These factors will combine to make for a very clean air quality day, with concentrations well within the Good range.

This rainy system will take its sweet time moving northeastward out of the region, with the surface low pressure center stretching from western PA to NJ on Sunday morning. The winter storm-like comma shape of this system will keep clouds and showers in western PA and western MD throughout the day and drape a southward extending cold front along the eastern seaboard. While this front will promote scattered showers at areas along the coast on Sunday, inland locations in the central and southern Mid-Atlantic (SMA) will see blue skies by 18Z. An overall Good air quality day is expected, mostly due to Saturday’s washout. Clouds are expected to clear out of the northern Mid-Atlantic (NMA) overnight.

Although a center of surface high pressure will establish itself over VA on Monday morning, an approaching cold front from the Great Lakes will make the impact of clear skies over the Mid-Atlantic short lived. Another surface wave approaching from the west will allow clouds to build throughout the NMA throughout the afternoon and evening. Light surface winds and sunny skies for much of the day will help increase ozone and PM2.5 concentrations to the top of the Good range.

Tuesday will be another day of cloud cover and rain showers as the tail end of a stationary front reaches through NJ and into central MD and yet another cold front approaches from the northwest. Specifically, the NMA is expected to see the heaviest precipitation in the late afternoon. The presence of clouds and the promise of late-day showers spell another day of Good air quality for the Mid-Atlantic on Tuesday. Wednesday will see much of the same as the cold front reaches northwestern PA and a lee trough stretches across the Delmarva and southwestward through central VA. Although this trough will present a focus for convergence and little else during the morning hours, pre-frontal clouds and showers will spread across much of the northern and central Mid-Atlantic by the early evening. Ozone and PM2.5 are again expected to stay within the Good range.
-Eherts/DeBoe/Ryan