textproduct: Raleigh

WHAT HAS CHANGED

* Nothing appreciable

KEY MESSAGES

As of 300 PM Monday...

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

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

3) Still a chance for more rain from Friday to Sunday.

DISCUSSION

As of 300 PM Monday...

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

The remains of what will likely be widespread strong to severe storms centered over the mid MS Valley this afternoon-evening are expected to weaken with time and ewd extent into and across the srn and cntl Appalachians Tue morning, where foregoing deep dryness and stability will exist from both preceding mid/upr-level ridging and an EML that has advected from the cntl Rockies to the srn Middle Atlantic during the past couple of days. Mostly stratiform rain, and mid-level ceilings centered in the 7-12 thousand ft layer, will result over the wrn NC Piedmont. The NAM and its 3km nest are (high) outliers with respect to both QPF and MUCAPE of up to a few hundred J/kg rooted atypically high and around 700 mb in their simulations and are considered unlikely to verify. Instead, rainfall amounts are expected to be less and mostly between a hundredth and tenth of an inch where any reaches the ground over the wrn Piedmont. In fact, convection-allowing (HREF) ensemble guidance indicates a 30-50% probability of 0.01" over the nw Piedmont, with a 10% probability of greater than 0.10" over the far nw Forsyth Co. LREF probabilities of those amounts are slightly higher: 10-75% of 0.01" over the wrn half of cntl NC (roughly west of US Hwy 1) and 10-30% of 0.10" over the nw Piedmont.

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

Aloft, a pair of s/w disturbances will track ewd across the TN Valley/Deep South Tue night then continue across the mid- Atlantic/Carolinas on Wed and offshore Wed night, all while the parent low swings across Ontario, Canada. The leading disturbance appears to be about 3-6 hrs ahead and further south than the trailing, nrn stream s/w. At the surface, a warm front will lift newd across central NC as a low tracks ewd across the nrn mid- Atlantic/Northeast on Wed. The trailing cold front should also progress ewd across the Appalachians on Wed and continue across the area Wed night as the parent low shifts offshore of NJ/NY. Note the track of the parent low and timing of the cold front still varies from model to model. The 12Z NAM is the quickest to bring the front through (Wed evening).

Expect some rain/showers late Tue night/Wed morn with the leading s/w disturbance as the warm front lifts nwd into the area. This early precipitation could impact the available instability with the trailing s/w and thus potential for storms to become severe. The trailing s/w should move across at a more favored diurnal time, if earlier activity does not limit destabilization. NAM forecast soundings show deep layer shear of 40+ kts with SBCAPE in the 500- 1000 J/Kg range Wed aft/eve, while the GFS also has 0-6 Km shear of 40+ kts but SBCAPE limited to less than 300 J/Kg over the Triad, with little if any instability noted elsewhere. Will have to monitor how this evolves in the coming days, but there is at least a conditional threat for isolated strong to severe storms on Wed across central NC and a Marginal (Level 1) Risk of severe storms in in place from the SPC. Both the 12Z NAM and 06Z GFS show a brief period of 30-40 kt winds at 925 mb, mainly across the south, Wed morn/early aft, so if the earlier convection is able to tap into that, there could be some stronger gusts in that range with them.

KEY MESSAGE 3... Still a chance for more rain Fri-Sun.

There area still some timing/track differences with the next weather system as it moves across the srn CONUS late-week into the weekend. Aloft, the nrn stream low over srn Ontario/nrn Great Lakes Thu/Fri should drift slowly ewd across the Northeast US/Quebec, Canada through the weekend. Meanwhile, a srn stream low is expected to move inland near nrn Baja/srn CA Thu/Thu night and should track ewd into the srn Plains by Fri/Fri night. The model variability increases significantly beyond Fri, with the GFS showing the s/w getting picked up by and amplifying the nrn stream trough then ejecting quickly newd into and across the region Fri night/Sat, while the EC solution is slower and less amplified, with a slightly farther south trajectory of the s/w across the Southeast US Sat/Sun. For central NC the GFS solution is wet, while the EC is dry.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

As of 1241 AM Monday...

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.