Forecast Discussion

Date: Wednesday, August 21, 2019

Forecast Valid: Thursday, August 22, 2019

Today's Air Quality Conditions: Air quality levels are in the Code Green range statewide this afternoon. For a display of the most recent air quality conditions throughout the remainder of this afternoon, please visit the US EPA's AIRNOW web site.

General Forecast Discussion: Tomorrow, a strong upper level low -- trapped by a continuing west-based, negative NAO block over Greenland -- will pivot southeastward towards the Great Lakes/New England. This will result in cyclogenesis over southeastern Quebec, and will result in a weak surface trough extending southward down the Appalachians into NC. This will provide a catalyst for afternoon showers and thunderstorms, and the current expectation is that this should continue to hold air quality levels predominantly in the Code Green range through the period. However, short-term model performance -- especially the NAM -- has been particularly poor the past 30 to 60 days, and once again it appears to be trending completely away from a solution it held a mere 24 hours ago. The new trend is towards less clouds as it slows down the arrival of another batch of PVA, which may result in a mostly sunny mid to late afternoon. This is a big deal for air quality forecasts, which don't get the luxury of a probabilistic approach to convection. Will have to go with the latest trends and hedge ozone levels upwards into the low Code Yellow range in the Charlotte and Triangle regions based on the latest trends, with Code Green forecast elsewhere across the state.

Outlook: By Friday into Saturday, a strong cold front will approach the region from the north, but as is typical for this time of year it may stall near or across the state. The NAM suggests the front could push further south, but has become operationally near-worthless beyond 12 hours out, so it will be disregarded henceforth. Additionally, a weak area of low pressure may attempt to develop along the front, and depending upon where the front ends up, this could result in a mostly cloudy, dreary day with off and on showers, which is what appears most likely to happen at this point. With this in mind, air quality levels should continue to remain in the Code Green range across the state, unless this setup evolves.

Extended Air Quality Outlook
Forecast Day
AQI Range
Category Range
Thursday 50-61 Green-Yellow
Friday 30-45 Green
Saturday 30-45 Green

(McLamb - NC Division of Air Quality)


Date: Tuesday, August 20, 2019

Forecast Valid: Wednesday, August 21, 2019

Today's Air Quality Conditions: Air quality levels are in the Code Green range statewide this afternoon. For a display of the most recent air quality conditions throughout the remainder of this afternoon, please visit the US EPA's AIRNOW web site.

General Forecast Discussion: Tomorrow into Thursday, a strong upper level low -- trapped by a continuing west-based, negative NAO block over Greenland -- will pivot southeastward towards the Great Lakes/New England. This will result in cyclogenesis over southeastern Quebec, and will result in a weak surface trough extending southward down the Appalachians into NC. This will provide a catalyst for afternoon showers and thunderstorms, and the current expectation is that this should continue to hold air quality levels predominantly in the Code Green range through the period. A few hours of clear skies may allow Charlotte ozone levels to temporarily rise into the Code Yellow range tomorrow afternoon, so as a precaution have forecast a low Code Yellow for ozone there, with Code Green forecast elsewhere across the state.

Outlook: By Friday, a strong cold front will approach the region from the north, but as is typical for this time of year it may stall near or across the state. Additionally, a weak area of low pressure may attempt to develop along the front, and depending upon where the front ends up, this could result in a mostly cloudy, dreary day with off and on showers, which is what appears most likely to happen at this point. With this in mind, air quality levels should continue to remain in the Code Green range across the state, unless this setup evolves.

Extended Air Quality Outlook
Forecast Day
AQI Range
Category Range
Wednesday 45-58 Green-Yellow
Thursday 30-45 Green
Friday 30-45 Green

(McLamb - NC Division of Air Quality)