Medium Range Air Quality Outlook
Mid-Atlantic Region
Issued: Sunday, July 13, 2014
Valid: July 14 – 18 2014 (Monday-Friday)

Summary:

Monday will see rain and thunderstorms in the second half of the day as a cold front approaches from the west. Cloudy skies and sustained surface flow will limit ozone to the Good range. PM2.5 will reach the Moderate due to warm air advection aloft and increased moisture. The cold front will pass through Tuesday, which will clean everything out limiting air quality to the Good range. The cold front will reach the coast on Wednesday, resulting in precipitation mainly along areas closest to the frontal boundary. Air quality will remain in the Good range. High pressure will move in overhead for Thursday and Friday. Sunny skies and calm weather will bring ozone into the Moderate range while PM2.5 will remain in the Good range for both days.

Discussion:

The weather forecast models are in good agreement for the medium range period. The beginning of the period will start with a closed low over the Great Lakes region. It will weaken and move through the Mid-Atlantic through the week. The ECMWF and the GFS start to diverge on Thursday morning when the ECMWF develops a strong shortwave over Ohio. This will affect the precipitation forecast in the northern Mid-Atlantic for Thursday and Friday.

A lee-side trough will develop on Monday, creating a chance for rain and thunderstorms for the second half of the day. Winds will pick up along with cloud cover reducing ozone to the Good range for most locations. With humidity and warm air advection aloft, PM2.5 will rise into the Moderate range for most locations.

The lee-side trough will remain on Tuesday as a cold front from the west moves through the region, keeping the high chance for rain and thunderstorms primarily in the second half of the day. Northwesterly flow aloft and cloud cover will keep air quality in the Good range for most locations.
As the cold front slowly moves through the region, Wednesday will see rain showers mainly along the coast and the southern Mid-Atlantic. The day will be mostly cloudy with northerly surface flow. Air quality will remain in the Good range.

High pressure will move in overhead as the cold front moves off the coast on Thursday, resulting in sunny skies and calm weather. Air quality will remain in the Good range yet there will be a chance for scattered Moderate ozone. High pressure will stay overhead for Friday keeping the sunny skies and calm weather. Ozone will rise into the Moderate range for most locations while PM2.5 will remain in the Good range.

-Catena

Medium Range Air Quality Outlook
Mid-Atlantic Region

Issued: Saturday, July 12, 2014
Valid: July 13 – 17 2014 (Sunday-Thursday)

Summary:
As a cold front approaches the Mid-Atlantic region on Sunday, there will be mostly to partly cloudy skies and a slight chance for afternoon rain. Ozone will be limited to the Good range while PM2.5 will reach the Moderate due to increased moisture and warm air advection aloft. Monday will be similar to Sunday’s conditions as the cold front travels closer to the region. Ozone will remain in the Good range and PM2.5 will stay in the Moderate. The front will slowly pass through on Tuesday and Wednesday leaving rain and thunderstorms. Air quality will be reduced to the Good range for both days. High pressure will move into the region on Thursday as the cold front retreats to the coast. The day will be mostly sunny and calm. PM2.5 will remain in the Good range while ozone will have the chance to reach Moderate.

Discussion:

The weather forecast models are in good agreement for the medium range period. Sunday will start with an intense upper level closed low over southern ON/Great Lakes and will move southeastward through the week. The GFS and the NAM diverge from the ECMWF starting Monday afternoon when they move the bulk of the energy from the upper level low faster northeastward than the ECMWF. The ECMWF keeps the energy centered over the Great Lakes region. By Tuesday morning, the GFS and the NAM feature the lobe of energy over ON/QC while the ECMWF keeps it stationed over the Great Lakes. The models do show similar placement of the trough and will stay in phase with each other for the rest of the period.

Sunday will be partly to mostly cloudy with sustained southerly surface winds due to cyclonic flow aloft. As a cold front approaches from the west, there will be a slight chance for late afternoon rain and thunderstorms primarily in the northern Mid-Atlantic (NMA). Ozone will be limited to the upper Good range for most locations while PM2.5 will reach the Moderate due to increased moisture and warm air advection aloft. There is a chance for Moderate ozone along the I-95 Corridor in the NMA.

A lee-side trough will develop on Monday, creating a chance for rain and thunderstorms for the second half of the day. Vertical mixing will be reduced as warm air advection continues aloft. Sustained southerly surface winds and mostly cloudy skies will keep ozone in the Good range. PM2.5 will remain in the Moderate range for most locations due to stagnant conditions aloft and high levels of moisture.

By Tuesday, the cold front will reach the Mid-Atlantic in the late afternoon. The passage of the front will create rain and thunderstorms for primarily the second half of the day on Tuesday. Northwesterly flow aloft and cloud cover will keep air quality in the Good range for most locations.

As the cold front slowly moves through the region, Wednesday will see rain showers mainly along the coast. The day will be partly sunny with westerly surface flow. Air quality will remain in the Good range. As the cold front moves of the coast on Thursday, high pressure will move in overhead, resulting in sunny skies and calm weather. There will be a potential rise in ozone to the Moderate range for most locations but PM2.5 will remain in the Good range.

-Catena

Medium Range Air Quality Outlook
Mid-Atlantic Region

Issued: Friday, July 11, 2014
Valid: July 12- 16, 2014 (Saturday-Wednesday)

Summary:

There is a chance for ozone to reach the USG range at isolated locations in the northern Mid-Atlantic (NMA) on Saturday due to overnight stagnation, lights winds, and mostly to partly sunny skies. PM2.5 will reach the low Moderate on Saturday for most locations. Sunday will see the development of a lee-side trough and an approaching cold front. Partly sunny skies and sustained southerly flow will reduce ozone to the upper Good range with the exception of along the NMA I-95 Corridor, where Moderate conditions are likely. PM2.5 should remain in the Moderate due to an increase in atmospheric moisture. Monday will see afternoon rain and thunderstorms as a cold front approaches from the west. Ozone will be reduced to the Good range for most locations, while PM2.5 will remain Moderate. Tuesday and Wednesday will have Good air quality as the passage of the cold front will potentially produce heavy rain and thunderstorms for both days.

Discussion:

The weather forecast models are in close agreement for the medium range period. The 00Z ECMWF, 06Z GFS, and the 06Z NAM all agree on mainly zonal flow aloft for Saturday. Sunday will have cyclonic flow aloft as a large closed low over south-central Canada will move eastward. The closed low will split off a lobe of energy late Sunday into Monday morning, which elongates an amplifying longwave trough over the eastern U.S. The bulk of the energy will stay centered over the Great Lakes on Tuesday morning, which will pull a cold front through the Mid-Atlantic on Tuesday and Wednesday. The models diverge beginning late Tuesday into Wednesday. The ECMWF keeps the closed low over the Great Lakes, while the GFS is more progressive, and opens up the trough and moves the bulk of energy northeastward into QC. Given the GFS’s faster solution, it moves the cold front off the coast earlier than the ECMWF, resulting in drier conditions for Wednesday afternoon along the coast.

A stationary front will move off the East Coast Saturday morning as high pressure moves offshore. Saturday’s weather conditions look to be very similar to Friday’s. Overnight stagnation, light winds during the day, and mostly sunny skies will allow ozone to reach the upper Moderate along the I-95 Corridor in the NMA, with a chance for isolated USG. The NOAA and BAMS air quality models are consistent again this morning with predicting a band of upper Moderate to isolated USG ozone along/north/west of I-95 from northern NJ to VA. PM2.5 will reach the Moderate range for most locations due to the surface stagnation.

By Sunday, a surface ridge of high pressure associated with the Bermuda High will expand over the Mid-Atlantic, keeping the region mostly dry. There is a slight chance for rain showers in the afternoon in the northern Mid-Atlantic (NMA) due to an approaching cold front stationed over the Great Lakes and the development of a lee-side trough. Overnight and through the early morning, a shortwave moving through the Great Lakes into NY State will trigger rain showers in the northwest portion of the Mid-Atlantic. For the rest of the region, the day will be partly sunny with sustained southerly flow. Ozone will reduce to the Good range for most locations, with the exception of along the I-95 Corridor in the NMA. PM2.5 will stay in the Moderate range for most locations in the NMA due to an increase in moisture yet should stay in the Good range in the southern Mid-Atlantic (SMA).

A lee-side trough will remain over the Mid-Atlantic on Monday as the cold front moves closer to the region. Afternoon rain and thunderstorms will occur mainly in the NMA in areas along the trough. Partly to mostly cloudy skies and southwesterly surface flow will keep ozone in the Good range for most location. Moderate ozone is possible in areas that see afternoon sun. PM2.5 will remain in the Moderate range in the humid air mass.

There will be rain and thunderstorms all day on Tuesday and Wednesday as the cold front slowly passes through the Mid-Atlantic. As the front travels halfway through the Mid-Atlantic on Tuesday, it will bring southwesterly flow aloft. Both days should see Good air quality as the cold front will produce heavy storms and all-day cloud cover.

-Catena/Huff

Medium Range Air Quality Outlook
Mid-Atlantic Region

Issued: Wednesday, July 9, 2014
Valid: July 10- 14, 2014 (Thursday-Monday)

Summary:

High pressure will move over the Great Lakes leaving the Mid-Atlantic mostly sunny with northerly flow while the southern Mid-Atlantic will experience rain and thunderstorms as a cold front stalls over NC. Air quality will be limited to the Good range for most locations. Sunny skies and northerly flow will remain in the northern Mid-Atlantic as the high pressure sits over the Great Lakes. The southern Mid-Atlantic will continue the rainy weather as the cold front will stall over NC. Air quality will remain in the Good range for Friday. The center of high pressure will move over New England on Saturday bringing easterly flow to the northern Mid-Atlantic. There is a slight chance of precipitation with partly cloudy skies. Air quality will remain in the Good range with the exception of scattered Moderate ozone in the northern half of the region. Sunday will have rain and thunderstorms later in the day as a cold front approaches from the west. The day will be mostly to partly sunny resulting in Moderate air quality. Monday will have all day rain and clouds reducing air quality to the Good range.

Discussion:

The weather forecast models are in good agreement for the medium range period. An upper level trough will pass through the area by Friday evening with a weak ridge immediately following behind. The models have come in slightly better agreement for the weekend with the exception of the discrepancies between minor shortwaves passing through the area. An upper level closed low will form over MB Saturday morning and will intensify and move eastward through the medium range period. By Monday, it will station north of the Great Lakes region. This will produce some potentially heavy rain for early next week yet it is still uncertain for this far out in the forecast.

A frontal boundary will stall over NC on Thursday as a center of high pressure moves in over the Great Lakes. The front will create rain and thunderstorms for most of the region but primarily in the southern Mid-Atlantic. Mostly cloudy skies and northerly flow will limit air quality to the Good range for Thursday.

The rain will continue in the southern Mid-Atlantic until late afternoon Friday as the cold front stalls over NC. The center of high pressure over the Great Lakes will allow northerly flow and partly to mostly sunny skies for the northern Mid-Atlantic. The southern Mid-Atlantic will have southerly transport aloft and mostly cloudy skies. Air quality will remain in the Good range for most locations.

By Saturday morning, the cold front will move to the NC/SC border as a stationary front. The center of high pressure will move eastward over New England resulting in easterly flow and mostly sunny skies for the northern Mid-Atlantic. The region should mostly stay dry with the exception of a slight chance for precipitation in the southern part of the region as the high will extend its associated ridge down through the region. Air quality will remain in the Good range for most locations with the exception of scattered Moderate ozone in the northern part of the region.

A cold front will approach from the west on Sunday as the stationary front in SC will now move northward as a warm front. There is a chance for rain later in the day as the cold front moves eastward. Most locations should have Good air quality although there will be scattered areas of Moderate ozone for locations receiving the most sunshine. By Monday, a pre-frontal trough will develop over the Mid-Atlantic as the cold front moves closer resulting in scattered rain and thunderstorms all day throughout the region. Air quality will be reduced to the Good range.

-Catena/Ryan

Medium Range Air Quality Outlook
Mid-Atlantic Region

Issued: Monday, July 7, 2014
Valid: July 8- 12, 2014 (Tuesday-Saturday)

Summary:

A cold front will approach the Mid-Atlantic from the west and will travel overhead and stall over the southern Mid-Atlantic from Wednesday-Friday. The northern Mid-Atlantic will see mostly to partly sunny skies and westerly transport aloft, allowing Moderate air quality Tuesday-Friday. Rain and thunderstorms along with cloud cover in the southern Mid-Atlantic will limit air quality to the Good range. By Saturday, a center of high pressure over CT will result in easterly flow, keeping air quality in the Good range for most locations throughout the Mid-Atlantic.

Discussion:

There is high confidence in the weather forecast models for the medium range period. The beginning of the period shows the eastward movement of an upper level trough stationed over the Great Lakes region. It will gradually move eastward through the Mid-Atlantic and will somewhat weaken by Friday night. The ECMWF and the GFS begin to diverge overnight Friday as the ECMWF develops a more intense shortwave over the Great Lakes. The ECMWF then develops the shortwave into a small trough while the GFS forecasts a more zonal flow aloft. This will affect the precipitation and air quality forecast for the weekend.

Tuesday will see clouds and weak convection as a pre-frontal trough develops over the Mid-Atlantic region. An approaching cold front from the west will travel to western PA by Tuesday evening and will create a slight chance for late afternoon rain showers primarily in the northern half of the Mid-Atlantic. Sustained southwesterly flow with some cloud cover will keep air quality in the Good range for most locations. Moderate ozone is expected along the I-95 Corridor mainly in PHL, DE, MD, and NJ.

The cold front will travel over the Mid-Atlantic throughout Wednesday resulting in scattered rain and thunderstorms lasting from the afternoon to the evening. Westerly flow aloft from the Ohio River Valley will increase the potential for Moderate PM2.5 primarily in the northern Mid-Atlantic region. Cloud cover and steady surface winds will keep ozone in the Good range for most locations throughout the Mid-Atlantic with the exception of Moderate ozone along the northern I-95 Corridor.

By Thursday morning, the cold front will hover over the Delmarva Peninsula down through central NC and will stall for the remainder of the day as a stationary front. Rain and thunderstorms with cloud cover will mainly occur in the southern Mid-Atlantic for the second half of the day, limiting air quality to the Good range. Mostly sunny skies and continued westerly transport aloft will allow Moderate air quality in the northern Mid-Atlantic.

The front will still linger over eastern VA and NC on Friday. High pressure will move in over the western NY/PA border, resulting in mostly sunny skies for the northern Mid-Atlantic. Moderate air quality will remain for Friday in the northern half of the Mid-Atlantic. Scattered rain and thunderstorms will continue over the southern Mid-Atlantic, keeping air quality in the Good range. The stationary front will stall until Saturday morning and move somewhat northward throughout the day to Philadelphia overnight. The northern Mid-Atlantic will see partly sunny skies with a slight chance for precipitation. The center of high pressure will move over CT, resulting in easterly flow to the Mid-Atlantic. Air quality should be reduced to the Good range for most locations on Saturday, although, as noted above, there is divergence between the medium range weather models beginning Saturday.

-Catena/Ryan