textproduct: Raleigh

WHAT HAS CHANGED

* Increased chances for rain on Saturday.

KEY MESSAGES

As of 235 AM Tuesday...

1) Decaying remnants of upstream convection may produce light rainfall amounts over the wrn NC Piedmont early this morning.

2) Marginal Risk (level 1 of 5) for isolated severe storms on Wednesday.

3) A coastal low and shortwave trough are expected to bring an additional round of rain to the region on Saturday.

DISCUSSION

As of 236 AM Tuesday...

KEY MESSAGE 1... Decaying remnants of upstream convection may produce light rainfall amounts over the wrn NC Piedmont early this morning.

Convective debris clouds associated with upstream convection over the Ohio Valley have started to trickle across central NC this morning. A few radar returns are starting to show ahead of the main convective line over the far eastern TN mountains. Overall latest guidance still supports most of this convection largely eroding over the southern Appalachians and dissipating with eastward extent. Forecast soundings in the Triad depict a relative dry layer in the 800 to 900 mb levels, with saturation largely from 700 mb up. As such, still expecting any showers that do make it into the western Piedmont to only produce trace to a few hundreds of an inch. A few gusts of 15 to 25 mph may be possible with any showers this morning. Otherwise expect mostly cloudy skies today with a few breaks this afternoon. Highs in the lower 70s are expected.

KEY MESSAGE 2... Marginal Risk (level 1 of 5) for isolated severe storms on Wednesday.

An initial short-wave will eject out of the deep south Tuesday night into Wednesday morning generating convection across the southeast. The latest HREF simulates morning convection moving west to east across central NC from ~12Z to 18Z. Remnant convective cloud cover form this early convection may limit destabilization later Wednesday afternoon and evening. However, if destabilization can be realized later Wednesday afternoon, strengthening shear associated with an approaching upper jet may promote a period of possible organized convection along the sfc cold front.

While some high-res guidance would suggest that the kinematics may be more favorable for organized convection further north into VA, the latest HREF does pinpoint the highest updraft helicity neighborhood probabilities over much of the NC Piedmont and Sandhills. Again, we'll have to see how much early morning cloud cover and rain lingers, but there is surely a signal for potential isolated severe convection late Wednesday afternoon and into the evening.

Any lingering precipitation should largely dissipate through Thursday morning as zonal flow moves in aloft.

KEY MESSAGE 3... A coastal low and shortwave trough are expected to bring an additional round of rain to the region on Saturday.

The next rain maker should come from a low pressure system forming off the coast of the Carolinas and merging with a shortwave trough that will be moving through the Southeast. This system looks to reach the region sometime Friday or Saturday. Ensembles and deterministic models are coming into better agreement with a low forming somewhere off the coast, however strength and location is still uncertain. Regardless, the chance for a widespread, much needed rain across central NC is increasing Saturday. The spread in rainfall amounts is still large, with the mean of the GEFS showing the region receiving around 1-1.2 inch of rain in a 24 hour period ending late Saturday night, while the European ensemble shows around 0.4-0.7 inch in the same time period. These amounts have however trended up significantly from yesterday's runs. Rain should move out of the area late Saturday night, with an area of high pressure returning to the region.

AVIATION /10Z TUESDAY THROUGH SATURDAY/

As of 600 AM Tuesday...

10Z Update: Convection has reached the Triad a bit earlier than expected. Have massaged TAFs at KINT/KGSO to account for this earlier arrival. The more energetic convection is still lagged out over eastern TN, but there is still some lightning associated with the rain reaching the Triad this morning. Will hold onto the TEMPO group here for a potential 20 kt gust and reduce visibility for a few hours this morning. Although, suspect the lightning activity should diminish with time here. Currently watching a line of deeper convection over the NC Foothills that's translating pretty quickly eastward. Current track has it just missing south of KINT/KGSO, but will continue to monitor and possibly up gusts if needed.

Latest guidance has become a bit more bullish hanging onto MVFR (with perhaps some IFR at KINT at times) ceilings possibly through early afternoon today. Afterwards, a period of VFR conditions will persist through ~08 to 12Z when sub-VFR ceilings will spill in from the west along with possible overnight convection.

Previous discussion:

VFR conditions persist early this morning. Upstream convection will decay as it reaches and pushes east across the southern Appalachians. Still could see a few showers at KINT/KGSO between ~11 and 15Z, and maybe a rouge shower as far east as KRDU. Associated MVFR ceilings are possible at KINT/KGSO (perhaps some brief IFR ceilings with any showers) during that same temporal range. A few gusts to 15 to 20 kts may be possible with any passing showers at KINT/KGSO as well. Beyond this morning, expect multi-layer VFR cloudiness to persist through much of the 24 hr TAF period with light swly flow.

Outlook: IFR-MVFR ceilings and another area of mostly stratiform rain are expected to overspread cntl NC Wed morning, followed by a chance of showers and storms along a passing cold front during the late afternoon and evening. Another chance of flight restrictions and rain will accompany an area of low pressure forecast to track across or just south of the Carolinas late Fri night-Sat.

RAH WATCHES/WARNINGS/ADVISORIES

None.