Daily Archives: June 3, 2014

Mid-Atlantic Medium Range Air Quality Discussion, Issued Tuesday, June 3, 2014

Medium Range Air Quality Outlook
Mid-Atlantic Region

Issued: Tuesday, June 3, 2014
Valid: June 4 – June 8, 2014 (Wednesday-Sunday)

Summary:

As a cold front slowly moves through the Mid-Atlantic region PM2.5 will rise into the low Moderate range and O3 will be in the Good to low Moderate range. Good air quality Thursday due to convection and precipitation. High pressure will begin to move into the region Friday along with northerly clean flow from Canada. Good air quality Friday with a slowly modifying air mass over the weekend as high pressure moves overhead. Moderate air quality possible Saturday and likely on Sunday as mixing decreasing.

Discussion:

The forecast models diverge on the location and timing of a short wave disturbance moving in from the west on Thursday. However, these differences won’t have a huge impact on air quality concerns as all models predict significant precipitation during the day Thursday across the mid-Atlantic. They agree on the timing of the arrival of precipitation, roughly 1200 UTC Thursday but they vary as to the location of the heaviest precipitation and the ending time. The GFS moves the shortwave more southward while the ECMWF is more to the north and the NAM is well to north of both. We will consider the NAM an outlier due to its recent consistency with sending the shortwave more northward than both the ECMWF and the GFS. In any event, all models agree on ridging and fair weather for the weekend.

For Wednesday, a weak cold front will slowly cross the mid-Atlantic. Back trajectories predict clean air from a source region in southwestern Ontario. The models all agree that Wednesday looks to be mostly sunny and dry until late. The models show warmer air aloft in the southern part of the region, which translates to more stable conditions and stagnant air. PM2.5 concentrations will reach the low Moderate range in the southern part of the region and the high Good range in the northern part. Ozone concentrations will be in the Good to low Moderate range. Highest ozone will occur east of the I-95 Corridor with magnitudes depending on the possibility of late day recirculation from the sea breeze.
By 12Z Thursday, the low pressure system from Ohio moves to the Delmarva Peninsula (we are discounting the more northern NAM track). Although the models show differences, as noted above, they agree that there will be precipitation starting early Thursday morning and lasting until the afternoon. Precipitation will be strong enough to bring PM2.5 concentrations back into the high Good range while clouds and rain keep ozone concentrations in the Good range as well.

The center of the low and its associated cold front will move through New England Friday with a region of high pressure centered over Indiana. Northerly air will flow from Quebec bringing in cleaner air conditions. There is expected to be lingering precipitation in North Carolina for most of Friday. Concentrations of both ozone and PM2.5 will remain in the Good range.

The region of high pressure will move overhead by Saturday 12Z. Good PBL mixing is expected on Saturday with good to low moderate air quality. As we work into June, the long day length and sunny skies may allow scattered locations to reach the moderate range for ozone.

A low pressure system from the Midwest will move towards the Mid-Atlantic on Sunday but high pressure will remain in control as it will not pass through until Sunday night or Monday morning. Warm air advection will reach the area by 18Z Sunday, limiting mixing and leading to moderate ozone and PM2.5 concentrations.

-Catena/Ryan