textproduct: Raleigh

WHAT HAS CHANGED

* Air Quality Alerts in effect for the Triangle and Triad through Friday.

* Heat indices trending slightly downward for Friday.

KEY MESSAGES

As of 215 PM Thursday...

1) Air Quality Alerts in effect through Friday for the Triangle and Triad.

2) Hot temperatures and potentially dangerous heat expected into Saturday.

3) Becoming unsettled this weekend into early next week with increased precip chances.

DISCUSSION

As of 215 PM Thursday...

KEY MESSAGE 1... Air Quality Alerts in effect through Friday for the Triangle and Triad.

A hot and nearly stagnant air mass over the region today is favorable for the development of dangerous levels of ozone, primarily surrounding the main metropolitan areas of North Carolina. This has prompted a Code Orange from the NC Division of Air Quality around the Triangle and the Forsyth County Office of Environmental Assistance and Protection for the Triad. Although there is still lingering Canadian wildfire smoke over the area, especially over northeast NC, these fine particulates remain well above the surface and are not a contributing factor to the poor air quality over the area.

A similarly stagnant and hot air mass will remain over the area Fri and result in additional Code Orange Air Quality Alerts. We will also be watching for the addition of fine particulates currently streaming across NY/PA to work down into VA and potentially into the Piedmont of NC by Fri morning. However, the latest runs from the RRFS and to a lesser degree the HRRR, which both simulate near- surface smoke, have trended to keeping the highest concentrations mainly confined along and north of the NC/VA border. How far south dangerous levels of smoke will advect remains a point of uncertainty. Stay tuned for additional forecasts to come later this afternoon and potentially again Fri morning if the forecast changes.

KEY MESSAGE 2... Hot temperatures and potentially dangerous heat expected into Saturday.

An elongated mid-lvl ridge axis stretching from the lower Ohio Valley, across the Carolinas, and into the western Atlantic will continue to provide background subsidence over the region before breaking down on Sat. H850 temperatures of 19-22C observed in the 12z RAOBs over VA and into NC will continue to support hot temperatures over the region with minimal thermal/moisture advection into Sat. Overwhelming model support via low-lvl thickness and dry-adiabatic technique support statistical guidance as well as the National Blend to result in high confidence in 2m temperatures reaching the upper 90s to around 100 this afternoon and once again on Fri. However, confidence is lower with respect to dew points during peak heating and whether they will support multiple hours of heat indices in the mid/upper 100s, especially west of the US-1 corridor.

Forecast challenges: Model guidance remains consistent with northerly winds persisting over the Piedmont into peak heating where continued dry air aloft and some light downsloping component west of a weak pressure trough may help mix dew points into the low/mid 60s on Fri. Additionally within those northwesterly winds, haze/smoke from Canadian wildfires may be deposited into our area, which may further the temperature forecast. Finally, hi-res guidance is beginning to develop isolated to even locally scattered showers/storms Fri afternoon with cool outflow potentially limiting the window to reach heat indices around 105. Regardless on whether heat indices of 105 are met, light to nearly stagnant surface winds, abundant sunshine and hot temperatures will still provide a favorable air mass for heat related illnesses to occur among any individual who does not have access to adequate hydration or cooling.

KEY MESSAGE 3... Becoming unsettled this weekend into early next week with increased precip chances.

By Saturday the upper ridge will break down across the Mid Atlantic with broad northwesterly flow taking hold. A surface wave will develop across the Great Lakes and migrate southward on Saturday, making a run at NC late in the day. 00Z global ensemble cluster solutions are in fairly good agreement in that the front will hold short of crossing NC during the day on Saturday although there should be some modest instability and increasing moisture in place across NC to work with supporting the notion of carrying some PoPs across the area. Increased precip chances look to be focused more on Sunday when the front is in closer proximity to central NC. It's too early to pinpoint the finer details but one would think areas along and east of US-1 would stand a relatively higher chance of showers and storms where the atmosphere has longer to destabilize ahead of the front. There are some signals in the global ensembles and even some of the higher-res deterministic solutions that the tail end of the front may get hung up somewhere across the northern/central Coastal Plain Sunday night into Monday morning, perhaps serving as an additional focal point for continued shower chances into the overnight hours.

Meanwhile, the aforementioned weak upper wave across the northeastern Gulf will be drawn northward this weekend, potentially interacting with the stalled surface boundary. While the exact evolution of this upper wave remains uncertain and whether or not it obtains tropical characteristics (NHC currently projects a 20 percent chance of development), unsettled weather looks to linger into early next week.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

As of 750 PM Thursday...

Prevailing VFR conditions are expected. Although sub-VFR vsby can't be completely ruled out due to haze/smoke at the northern terminals Fri morning, model guidance is trending farther north with the southern extent of the higher concentrations of fine particulates from smoke. Isolated shower or brief storm will be possible anywhere within central NC Fri afternoon/evening.

Outlook: Increasing chances for diurnally driven showers/storms each afternoon heading into the weekend. A wavy frontal zone waffling over the region this weekend into early next week may result in a more active weather pattern to support sub-VFR conditions from stratus/mist overnight and scattered to locally numerous showers/storms in the aft/eve.

CLIMATE

Record temperatures within 3F of forecast ones...

Record Highs:

July 17: KRDU: 100/1887 KFAY: 102/1932 July 18: KGSO: 97/1986

Record High Mins:

July 17: KGSO: 75/2025 KFAY: 77/2019 July 18: KGSO: 76/1986 KFAY: 77/2025 July 19: KGSO: 75/2016 KFAY: 77/2023

RAH WATCHES/WARNINGS/ADVISORIES

Air Quality Alert from 10 AM to 8 PM EDT Friday for NCZ008-021>023- 025-038-039-041.