Daily Archives: June 11, 2018

Mid-Atlantic Medium Range Air Quality Discussion, Issued Monday, June 11, 2018

Medium Range Air Quality Outlook
Mid-Atlantic Region

Issued: Monday, June 11, 2018
Valid: June 12-16 (Tuesday-Saturday)

Summary

Surface high pressure moving southward into the northeast US will result in a cold air damming pattern across the Mid-Atlantic on Tuesday. Northeasterly flow aloft and widespread cloud cover will limit temperatures to below average values across the region. Conditions unfavorable for ozone formation will result in a Slight risk of an ozone exceedance. Unsettled conditions will continue on Wednesday as a wave of low pressure pulls a series of fronts through the Mid-Atlantic. Scattered showers and thunderstorms will keep the risk of an exceedance Slight. Thursday will be dry and seasonably warm across most of the Mid-Atlantic as the center of high pressure moves into the Ohio River Valley. A noticeably less humid air mass in the NMA and CMA will promote mostly sunny skies with a few clouds in the afternoon. In the SMA, above average temperatures, periods of sunshine and a lingering frontal boundary will result in a Marginal risk for an ozone exceedance.

Forecast model consensus breaks down by late Friday with some models suggesting a transition to a very warm, high ozone pattern by Saturday. Our confidence at this forecast lead time is low but USG ozone in the Mid-Atlantic during the weekend is quite possible particularly as we are moving into the climatological peak of the ozone season.

 

NWP Model Discussion

The weather models are in consensus with the progression of the synoptic pattern until late in the medium range period. The upper level ridge now just to our west will be suppressed by a strong wave moving along the northern tier states. This will reinforce the weak trough over the mid-Atlantic and sustain northwest flow aloft. By 06Z Thursday there will be three primary features over the CONUS; a longwave trough centered over southern ON/southwestern QC, a second longwave trough moving into the Pacific Northwest, and a broad upper/mid-level ridge building over the central US/Mississippi River Valley. The development and movement of the central US ridge will be the key air quality forecast factor for late in the period. By 12Z Friday, shortwave energy dropping into southern ON will reinvigorate the trough over the NMA and CMA. The evolution of this feature over the weekend is where the GFS and ECMWF begin to diverge. The ECMWF develops a stronger trough over the Mid-Atlantic that slowly moves offshore by 00Z Sunday. The GFS is weaker and more progressive, pushing the trough through New England and offshore by 12Z Saturday. The GFS solution will allow strong warm air advection from the west and is more conducive to high ozone in the Mid-Atlantic on Friday and Saturday.

 

The Dailies

Day 1 (Tuesday): Surface high pressure moving southward into the northeast US will result in a cold air damming pattern across the Mid-Atlantic on Tuesday. Northeasterly flow aloft and widespread cloud cover will limit temperatures to below average values across the region. A quasi-stationary warm front wrapping around the Appalachians will slowly push northeastward, encompassing the western and southern boundaries of the Mid-Atlantic by 00Z Wednesday. Most of the region will remain dry throughout the day, however, locations near the slow moving front will experience increasing cloud cover and periods of precipitation. Strong north/northeasterly flow, below average temperatures and cloud cover across the region is resulting in widespread Good ozone in the air quality models. Conditions unfavorable for ozone formation will result in a Slight risk of an ozone exceedance.

 

Day 2 (Wednesday): Unsettled conditions will continue on Wednesday as a wave of low pressure pulls a series of fronts through the Mid-Atlantic. A low pressure system moving through southern ON will pull a warm front northeastward into the CMA and NMA by 12Z Wednesday before an eastward advancing cold front enters the NMA shortly after. Widespread showers and thunderstorms will advance along the two fronts in the morning hours, with scattered showers lingering into the afternoon. The air quality models slightly increase regional ozone with widespread Good ozone and scattered Moderate ozone. The BAMS and NC models highlight locations along the MDL, WV, and VA with Moderate ozone possible in response to near average temperatures and a shift to westerly flow. The NC model and the BAMS-MAQSIP also highlight the Piedmont region of NC in response to slightly above average temperatures under increasing sunshine. Conditions will remain unfavorable for excessive ozone formation, keeping a Slight risk of an ozone exceedance.

 

Day 3 (Thursday): Thursday will be dry and seasonably warm across most of the Mid-Atlantic as the center of high pressure moves into the Ohio River Valley. A noticeably less humid air mass in the NMA and CMA will promote mostly sunny skies with a few clouds in the afternoon. In the SMA, above average temperatures and a lingering humid air mass will promote a mixture of sun and clouds with the possibility of a few scattered showers in the afternoon. With the exception of the NC-GFS, the air quality models are in agreement with widespread Good ozone across the NMA in response to a fast, northwesterly flow. The NC-GFS develops widespread Moderate ozone across most of the region. In the SMA, a lingering frontal boundary, periods of sunshine and above average temperatures are resulting in the development of widespread Moderate ozone south of the VA/NC border. The risk of an ozone exceedance will increase to Marginal on Thursday, with a focus on the SMA.

 

Day 4-5 (Friday-Saturday): Friday and Saturday are currently the primary days of interest but there is a lot of uncertainty in the forecast for Saturday. A few scattered showers and thunderstorms are possible on Friday as a weak back door cold front pushes into the NMA and CMA. Periods of sun and clouds will result in near average temperatures across the NMA and CMA, but in the SMA temperatures could reach above average values as the center of a mid-level ridge moves overhead. Weaker back trajectories in the CMA and SMA are resulting in mid-to-upper Moderate ozone across the region in most of the air quality models. The NC-GFS 2 is the most aggressive with widespread Moderate ozone with scattered USG across the Mid-Atlantic. Both BAMS models and the NC-GFS model highlight the Piedmont region of NC for elevated ozone with upper Moderate ozone in the BAMS-CMAQ and USG ozone in the BAMS-MAQSIP and NC-GFS2. Influence from mid-level ridging, above average temperatures and weak back trajectories, will result in a Marginal risk for an exceedance on Friday. Forecast model consensus breaks down by late Friday with some models suggesting a transition to a very warm, high ozone pattern by Saturday. Our confidence at this forecast lead time is low but USG ozone in the Mid-Atlantic during the weekend is quite possible particularly as we are moving into the climatological peak of the ozone season.

 

-Enlow/Ryan