textproduct: Raleigh

WHAT HAS CHANGED

* Marginal risk introduced across NC/VA border counties for an isolated stronger wind gust.

* Continued downward adjustment to high temperatures on Friday and Saturday.

KEY MESSAGES

As of 239 PM Thursday...

1) Increasing rain chances from north to south this afternoon through the overnight period. A few isolated stronger storms may be possible across the NC/VA border.

2) Cool and rainy over much of the Piedmont and nrn Coastal Plain Fri and Sat with a CAD wedge in place, warmer with some convection south and east of the wedge.

2) The wet pattern continues through mid-week. While it won't be raining the entire time at any given location, pockets of heavy downpours will be possible.

DISCUSSION

As of 239 PM Thursday...

KEY MESSAGE 1... Increasing rain chances from north to south this afternoon through the overnight period. A few isolated stronger storms may be possible across the NC/VA border.

Satellite analysis this afternoon depicted a few areas of lift associated with 1) a backdoor cold front and associated outflow surging through VA, 2) a wavering sfc low over the Outer Banks, and 3) weak mid-level vorticity traversing the southern Appalachians.

The weak perturbations over the southern Apps have triggered some showers and isolated thunderstorms over the Foothills and our Triad area. This activity should blossom with time across our western areas as low-level lapse rates have steepened to 8 to 9 C/km. Simultaneously, the backdoor front and associated outflow should trigger additional convection along our NC/VA border mid to late afternoon before sagging south through this evening and into the overnight period.

While shear is generally weak over our area today, 20 to 25 kts of effective shear will likely develop just to our north in VA before sagging south behind the front across the NC/VA border. If a few stronger storms can develop, isolated damaging wind gusts may be possible (especially given steep low-level lapse rates and DCAPE of 800 to 1000 J/kg). While a lesser threat today, a few rotating cells may be possible somewhere in the northeastern Coastal Plain later this evening. Forecast soundings in this vicinity indicate backed flow near the sfc just ahead of the advancing front/outflow. Not sure if enough sfc based instability will be present (near sundown), nor if LCLs would be low enough, but an isolated weak tornado may be possible.

Hydro wise, the latest REFS and HREF LPMM output continue to suggest a few swaths of 1 to 2 inches, with localized amounts of 2 to 3 inches may be possible through 12Z Friday. The general vicinity with the best chance for these higher amounts seems to be along and west of US-1 (additionally up towards the northern Coastal Plain). Given the recent drought, think the chance for flash flooding would be limited. However, can't rule out isolated ponding in low-lying areas/urban areas along with brief downpours which could make driving difficult.

Post-frontal gusty nely flow will linger a bit into tonight. Otherwise, expect the steadier precip to diminish near sunrise Friday morning.

KEY MESSAGE 2... Cool and rainy over much of the Piedmont and nrn Coastal Plain Fri and Sat with a CAD wedge in place, warmer with some convection south and east of the wedge.

Aloft, the sub-tropical ridge will strengthen and lift newd across the region Fri/Fri night. A s/w will follow, lifting newd across the region Sat/Sat night. At the surface, a CAD air mass should set up Thu night and remain in place through at least Fri night/early Sat across the NW and nrn Piedmont/nrn Coastal Plain as high pressure tracking across the Northeast US and offshore ridges swd into the area. With warm, moist air overrunning the cool, stable boundary layer within the wedge, expect overcast skies and rain to prevail. East and south of the wedge, an inverted trough and the quasi- stationary surface boundary will set up shop, generally from the sw Piedmont to cntl Coastal Plain. Expect primarily diurnally driven showers and storms in those areas. Still expect the wedge to erode sometime Sat night/Sun.

Precipitation: In the wake of the front tonight, warm air advecting in above the cooler, stable boundary layer should result in some rain through at least Sat over the nrn Piedmont, with showers and possible storms outside of the wedge airmass each day. Where/when the wedge erodes and a warm front lifts nwd across the area, there will be the chance for additional diurnally driven convection on the warm side of the boundary, while rain will be favored north of it.

Temperatures: There is still some bust potential wrt highs on Fri and Sat given the wedge air mass in place, especially if there is continued rain into it. For now have highs ranging from mid/upper 60s north to low/mid 80s south, but with below average confidence. On Sat, with the wedge lingering, highs currently forecast to range from upr 60s NW to mid 80s SE. Lows Fri night expected to range from mid 50s north to mid 60s south.

KEY MESSAGE 3... The wet pattern continues through mid-week. While it won't be raining the entire time at any given location, pockets of heavy downpours will be possible.

Aloft, high pressure will strengthen again off the Southeast US coast through middle of next week, with a s/w or two clipping the area as they pass to the north. The sub-tropical ridge will gradually build nwwd from the Southeast US to the upr MS Valley through Wed. At the surface, the wedge should erode by Sun night as a low tracks newd along the mid-Atlantic and Northeast US coasts. Sly to swly return flow around a strengthening, swd sinking Bermuda high over the Atlantic will advect warm, moist air into the region through mid-week. There is still some decent spread in the guidance wrt precipitation specifics from Sun onward, however do expect chances for diurnally driven convection each day. While it does not look like any given day will be a washout necessarily, there is at least a chance of showers and storms anywhere across central NC each aft/eve. Generally expect temperatures to moderate back to near or slightly above normal by early next week.

AVIATION /17Z THURSDAY THROUGH TUESDAY/

As of 1244 PM Thursday...

VFR persists at all terminals that afternoon under generally sunny skies. A cu field is starting to develop in the southern Piedmont/Foothills vicinity. Further north, a backdoor cold front and associated outflow has progressed through the middle of the Chesapeake Bay. This front and associated outflow boundary will promote increasing convection chances from north to south late this afternoon into the overnight period. A few isolated stronger thunderstorm downdrafts may be possible at KINT/KGSO/KRDU/KRWI this evening along heavy downpours and brief sub-VFR ceilings/visbys. As the front sags further south into central NC, expect some nely gustiness to follow and persist into the overnight period. Behind the front we'll also sock in everywhere, down to IFR/LIFR at all sites. Residual showers may persist at KINT/KGSO/KRDU through ~12Z but should clear north through the rest of the 24 hr TAF period. KFAY may lift to MVFR ceilings towards the end of the 24 hr TAF period, but everywhere else will likely remain IFR through late Friday morning.

Outlook: Sub-VFR ceilings should persist on Friday and Saturday over most terminals as a CAD regime looks to set up over the region. Widespread LIFR/IFR stratus is expected again on both Friday and Saturday nights. The best chance for ceilings lifting to VFR would be during the daytime on Friday and Saturday in the SE (including FAY), while INT and GSO may stay largely LIFR the entire time. While the CAD regime will start to break down on Sunday and Monday, low stratus will still be possible Monday morning. Daily shower/storm chances will also be possible through early next week.

CLIMATE

Record High Temperatures:

May 21: KRDU: 96/1941 KFAY: 99/1941

Record High Minimum Temperatures:

May 21: KGSO: 67/2022 KRDU: 71/1898 KFAY: 71/2025

May 22: KFAY: 73/2004

May 23: KFAY: 72/2011

May 24: KRDU: 70/2011 KFAY: 72/2000

May 25: KGSO: 70/2019 KRDU: 71/2019 KFAY: 71/2019

May 26: KGSO: 70/2019 KRDU: 73/2011 KFAY: 75/2004

RAH WATCHES/WARNINGS/ADVISORIES

None.