textproduct: Raleigh

WHAT HAS CHANGED

* There is a Marginal to Slight Risk of severe storms over Sampson, Cumberland, and Wayne Counties this afternoon and early evening.

KEY MESSAGES

As of 206 AM Monday...

1) There is a chance for showers and thunderstorms this afternoon to early evening along and east of the I-95 corridor.

2) Diurnally maximized convection returns to central NC as early as Wednesday, but more likely Thursday into Friday before shifting towards the coast through the weekend.

DISCUSSION

As of 206 AM Monday...

KEY MESSAGE 1... There is a chance for showers and thunderstorms this afternoon to early evening along and east of the I-95 corridor.

Satellite imagery and surface observations indicate a weak surface low developing over central SC, with a stalled cold front extending from the NC Coastal Plain into central SC. Dynamic guidance indicates the surface low will track east- northeast today into the Sandhills and central/southern Coastal Plain. As it does, the stalled front is expected to buckle westward, potentially reaching as far west as the Wake/Johnston county line.

A sharp moisture gradient remains across the state: the 00z MHX sounding highlighted a very moist airmass over eastern NC, contrasted with much drier air at GSO (PWAT of ~0.85 inches). Surface dewpoints in the mid-70s along the coast underscore the high moisture content east of the boundary. An enhanced seabreeze interaction with the front and surface low will serve as the primary trigger for convective initiation, with resultant outflows likely driving secondary cell development.

Spatial Focus & Model Guidance: The highest storm coverage is expected along and east of I-95, extending from the eastern Sandhills into the Coastal Plain. Most CAMs keep convective activity concentrated over the southern Coastal Plain (primarily Sampson and Wayne Counties). However, the RRFS represents a reasonable worst-case scenario, bringing convection as far west as the Harnett/Cumberland county line. While model spread leaves some uncertainty regarding exact western extent, the thermodynamic environment along and east of I-95 will easily support severe storms, characterized by MLCAPE of 2000-3000 J/kg (highest in Sampson County) and 30 kts of deep-layer shear. Should storms initiate further north near RWI, effective shear could reach ~40 kts under the influence of an upper-level jet streak.

Hazards: SPC expanded the Marginal Risk for severe thunderstorms, focused mainly over Sampson and Wayne Counties. The primary hazard will be locally damaging wind gusts, although a secondary hail threat is also possible given straight hodographs. SPC has also maintained a 2-percent tornado risk, where a Slight Risk of severe now exists over far southern Sampson; given weak bulk low-level shear, any brief tornado threat would be strictly non- supercellular, tied to localized low-level vorticity stretching along the surface low/boundary. Should 12z guidance and AI model trends continue shifting westward, further expansion of the severe risk westward may become necessary.

Drier, more comfortable conditions are expected Tuesday as high pressure builds in from the north. Lower dewpoints will maintain comfortable humidity levels across central NC. Isolated storm development will be largely suppressed, restricted to the sea breeze over Sampson or Cumberland counties. The aggressive HRRR solution was discounted in favor of global model consensus, which depicts a sufficiently stable airmass to prevent widespread activity.

KEY MESSAGE 2... Diurnally maximized convection returns to central NC as early as Wednesday, but more likely Thursday into Friday before shifting towards the coast through the weekend.

A closed mid/upper level low over southern Quebec Tues morning will continue to slowly pivot east-northeast as another series of shortwaves parade across Great Lakes and southern Ontario through Fri. Moisture returns in the low lvls as early as Wed, with deeper moisture return on Thurs, although rich tropical moisture appears limited in duration as the mid/upper level flow turns west-northwest again over the Mid-Atlantic into the Carolinas by this weekend. Nevertheless, this should support diurnally driven convection as surface dew points in the 70s return and PWAT values rise back to around or slightly-above normal into the weekend. There may be some mixing out of dew points each afternoon, especially over the Piedmont back into the 60s which may limit the moderate instability to the Sandhills and Coastal Plain.

Thurs still appears to have the best chance for measurable precipitation with neutral H5 height tendencies and potential influence from any MCV's from upstream convection over the Ohio and Tennessee Valley's. Reasonable high-end totals for any given area will be around 1" to as much as +2" based on the 12z LREF. However, these amounts will not occur everywhere, as is the nature of summertime convection, with most locations likely to receive somewhere between trace amounts to 0.5". Slow evolving longwave troughing to the west will favor southwesterly moisture transport over the area as early as Wed and continuing into Thurs night. This pattern could be conditionally favorable for excessive rainfall anywhere but highly dependent on training storms to develop.

AVIATION /12Z MONDAY THROUGH FRIDAY/

As of 620 AM Monday...

VFR conditions will generally prevail across central NC terminals through the period, with the primary exception being KFAY.

As a surface low tracks northward along a stalled front in eastern NC this morning, isolated showers and a storm may be possible until 13z at KFAY. However, most of the storms on radar presently should exit the terminal by 12z. However, additional convection is possible this afternoon.

This afternoon into the early evening, the surface low tracking northeast combined with a westward-buckling front and sea-breeze will bring a chance for isolated to scattered thunderstorms near KFAY. While the RRFS/HRRR/FV3 show convection reaching near KFAY, the majority of CAM guidance keeps activity just east of the terminal, justifying a low-end PROB30. Isolated storms are also possible near KRWI, but confidence remains too low to introduce terminal restrictions.

Outlook: Morning stratus and fog potential will be possible at KFAY/KRWI Tuesday and Wednesday mornings. Convective coverage will increase midweek, peaking Thursday and Friday, with impacts potentially lingering into early Saturday.

RAH WATCHES/WARNINGS/ADVISORIES

None.