Medium Range Air Quality Outlook
Mid-Atlantic Region

Issued: Sunday, June 8, 2014
Valid: June 9 – June 13, 2014 (Monday-Friday)

Summary:

An unsettled weather pattern is expected through the medium range. Temperatures will be in the low-mid 80’s F with partly to mostly cloudy skies and a chance of rain each day. The best chances for sustained rain will be Monday and Friday. Air quality will oscillate between Good and Moderate levels depending on the extent of clouds and precipitation at any location.

Discussion:

The weather forecast models are in good agreement through the medium range period with respect to the large scale features. Unfortunately for air quality concerns, the key air quality relevant weather factors will be embedded in mesoscale features that are more difficult to forecast beyond the short range.

A weak short wave will cross the Mid-Atlantic early Monday while a deeper trough to the west will “cut off” and stall over IL and move very little Tuesday and Wednesday. Finally, a “kicker” (short wave disturbance) from the northern Plains will push the remnants of the trough eastward Thursday, reaching the Mid-Atlantic early Friday. With southerly flow at low levels, a very humid air mass will be in place through the period so that any minor disturbances embedded in this generally unsettled weather pattern have the ability to produce precipitation and clouds. The weather forecast models differ on the timing and extent of precipitation after Monday and aren’t very well able to resolve these features. As a result, confidence in the day to day air quality forecasts depends on our confidence in the day to day precipitation forecasts. That is to say, not very good after Monday.

On Monday, an upper level disturbance will bring rain to the Mid-Atlantic. As noted above, there are differences in timing, location and extent of rain but cloud cover will be significant across the region. Ozone will be in the Good range, PM2.5 will rise along with humidity and should reach the Moderate range except where rain is heaviest.

Tuesday looks drier and while some locations will see afternoon showers, there will be enough sun to push temperatures into the mid-80’s F and ozone will reach the Moderate range. PM2.5 will continue in the Moderate range as well.

Wednesday and Thursday will be classic “chance of showers” days with very humid air in place and a warm front (associated with the trough stalled to our west) drifting northward through the mid-Atlantic. The precipitation forecasts at this range can’t be trusted so the best bet is to follow persistence with Moderate air quality both days. A cold front approaches on Friday with rain more likely. Ozone likely drops to the Good range but PM2.5 will remain Moderate.

-Ryan