textproduct: Raleigh

WHAT HAS CHANGED

* Although the Marginal (level 1 of 5) risk remains throughout cntl NC, the most likely window for the relative greatest threat will exist over the Piedmont between 8 PM and 11 PM.

* Updated the aviation discussion to reflect the latest thoughts on the convective evolution tonight and timing for the 00z Thurs TAFs.

KEY MESSAGES

As of 335 PM Wednesday...

1) Although the Marginal(level 1 of 5) risk remains throughout cntl NC, the relative greatest threat will exist over the Piedmont, mainly between 8 PM and 11 PM.

2) Next widespread chance for precipitation comes Friday night through Saturday night.

3) Temperatures will be near normal for the end of the work week drop below normal for Saturday and Sunday, then rise above normal for Tuesday and Wednesday.

DISCUSSION

As of 335 PM Wednesday..

KEY MESSAGE 1... Although the Marginal(level 1 of 5) risk remains throughout cntl NC, the relative greatest threat will exist over the Piedmont, mainly between 8 PM and 11 PM.

Widespread (low) overcast, and also subsidence in the wake of a convectively-amplified trough and MCVs across the Southeast since last night, have kept cntl NC stable and dry today. However, the poleward retreat of a warm front, which extended at 19Z from a lee low near HKY esewd across the Sandhills and srn Coastal Plain, will yield lifting and scattering of the low clouds and related ssw to nne diurnal destabilization across cntl NC through 22-23Z. Despite what may be a relative minimum in larger-scale forcing for ascent over cntl NC between now and 06Z, between the aforementioned convectively-amplified trough (and 70 meter 500 mb height falls observed at GSO at 12Z) and a perturbation that will shear quickly ewd from CO this afternoon to the srn Middle Atlantic early Thu, glancing influence from a couple of other shortwave perturbations pivoting across the Great Lakes may prove sufficient to support the development of showers/storms just upstream of cntl NC this afternoon-evening. Specifically, scattered cells may develop along a surface trough in the immediate lee of the Appalachians, one anchored by the aforementioned lee low near KHKY, and also possibly over the Blue Ridge in the next few hours - all of which should then move generally ewd with wly mean winds of 35-40 kts, and should some indeed develop, across cntl NC between 22Z and 03-04Z. VWP data and forecast hodographs depict veering in the lowest 2-3 kilometers beneath much stronger wly flow (50-90 kts) through the mid and upr- levels. Those (supercell) shear profiles will conditionally support splitting cells capable of producing hail and locally damaging wind gusts. Low-level shear will also be adequately strong to support isolated tornado potential, with strengthening of that shear with at least some nocturnal, low-level flow acceleration centered around 00Z. That isolated tornado potential would be highest for right- moving cells whose motions would be favorably aligned along the retreating surface warm front across the Piedmont, where both shear and low LCLs would also be relatively maximized.

KEY MESSAGE 2... Next widespread chance for precipitation comes Friday night through Saturday night.

Tonight's cold front will drop south along the Gulf Coast, become nearly stationary along the coast through Friday, then have a coastal low develop along the Atlantic coastline. While the forecast has trended drier for Friday evening, rain should begin to move into the region from south to north Friday night into Saturday, with the greatest chances of rain occurring Saturday morning. Rain chances will then decrease, coming to an end by midnight. While this is still three to four days away, the current forecast calls for anywhere between a quarter inch of rain in the Triad to an inch of rain in the southeast across Sampson county. Warmer temperatures between 500 and 700 mb should limit any instability and have removed any mention of thunder from the forecast.

KEY MESSAGE 3... Temperatures will be near normal for the end of the work week, drop below normal for Saturday and Sunday, then rise above normal for Tuesday and Wednesday.

While tonight's front will bring drier air into the region, the temperature of the new air mass will not be much different, and highs on Thursday and Friday should be in the low to mid 70s. As the coastal low develops, winds will take on a northerly component, resulting in a chilly day on Saturday - locations near the VA/NC border will struggle to reach 60 degrees, with low 60s elsewhere. With clearing skies on Sunday as the low departs, temperatures will climb slightly, but still remain mostly in the 60s. Monday will be a transitional day with temperatures near normal, then southerly flow will help raise highs into the 80s on Tuesday and Wednesday. Saturday night should be the coldest night, with temperatures ranging from the upper 30s to the mid 40s - too warm for concern about frost potential.

AVIATION /00Z THURSDAY THROUGH MONDAY/

As of 715 PM Wednesday...

MVFR cigs has cleared central NC terminals with scattered 3,500 to 5,000 ft cumulus in its wake. Convection along and immediately ahead of a cold front moving into/through southwest VA is expected to shift across central NC between 00z until approximately 05z. Scattered to locally numerous showers and mostly isolated thunderstorms may affect any central NC terminals and bring briefly heavy rain, risk for infrequent lightning, and gusty winds. Small hail can't be ruled out from the stronger convective clusters.

Areas of fog and stratus may develop in the wake of that convection early tonight, especially at RWI, amid residually moist low-levels and ahead of a cold front and following drier air and light nwly flow that will move across the region overnight. Mid and high-level (VFR) ceilings and occasional light rain may lift into FAY Fri morning; prevailing flight restrictions are not expected at this time.

Outlook: Rain and flight restrictions will accompany an area low pressure that is forecast to track along the coast of the Carolinas on Sat.

RAH WATCHES/WARNINGS/ADVISORIES

None.