Medium Range Air Quality Outlook
Mid-Atlantic Region

Issued: Saturday, July 18, 2015
Valid: July 19 – 23, 2015 (Sunday – Thursday)

Summary:

There is a high probability of scattered Code Orange ozone on Sunday lingering into Monday although convection, possible both early and late in the day, may limit ozone Monday. Particles will be in the Moderate range. A closed low forming over eastern Canada will bring seasonable weather for the remainder of the medium range period with Moderate air quality expected.

Discussion:

The forecast models are in good agreement through the medium range period. A closed upper level low will form over Hudson’s Bay on Sunday and then slowly move eastward to northern QC by Thursday. A series of disturbances will rotate around the low with the strongest disturbance moving through the Great Lakes on Tuesday bringing an end to a short period of very warm weather in the mid-Atlantic. Sunday and Monday will be the days of most interest for air quality concerns as it will be quite warm, mostly sunny and very humid.

For Sunday, all the ingredients for high ozone levels are expected to be in place: temperatures in the mid-90’s F, light and variable winds, particularly in the morning and early afternoon hours, westerly transport and moderately strong cap on convection. However, in recent years we have seen very few Sunday USG occurrences due to reduced emissions both locally and regionally. As a result, we expect only scattered USG ozone on Sunday.

Monday will remain very warm and, with the addition of weekday emissions, prime for another USG ozone day. However, the forecast models continue to bring early morning convection through the mid-Atlantic that will serve to take the edge off the carry over of pollutants and their precursors. The WPC has a weak cold front just west of the I-95 Corridor early Monday and passes it through the region during the day. This could act as a trigger for afternoon thunderstorms. The risk of USG ozone continues Monday although slightly less enhanced than Sunday. PM will be in the mid-upper Moderate range both days.

A secondary cold front associated with the Great Lakes trough will pass through the region Tuesday. The remainder of the medium range will feature normal temperatures, slightly drier conditions and steady west to northwest flow. This will translate into Moderate air quality through Thursday.

-Ryan