Key MESSAGE 1, A stationary front draped across the Southern Appalachians is forecast to lift slowly north and east through tonight in advance of a shortwave dropping southeast out of the Great Lakes. Modest moisture and instability along the boundary, plus enhanced convergence near a weak surface low traversing the boundary, appears sufficient for a convective cluster to develop along the higher terrain and drop southeast from central VA into northeast NC later today and tonight. Convective, global, and ensemble guidance have shown a consistently strong signal for this convective cluster despite only modest instability and moisture. That said, guidance is also in pretty good agreement depicting a weakening trend with the convection as it approaches ENC. Right now, it appears the greatest chance of seeing thunderstorms overnight will be from Lenoir County north through Martin County. The risk of severe weather appears low, but the environment appears supportive of some small hail or gusty winds in the strongest cores.
On Monday, daytime heating of the airmass in the vicinity of the seabreeze and any residual boundaries from tonight's convection should support a renewed risk of thunderstorms. Once again, some of these could be strong to marginally severe. Residually dry air aloft should support DCAPE values of 1000+ j/kg. This in tandem with steep low-level lapse rates and moderate instability should lead to the primary risk being damaging winds of 40-65 mph. Forecast aids like the ECMWF's EFI show a decent environmental signal for a few severe thunderstorms which is also supported by short-range ensemble guidance. The convective potential on Monday should primarily be diurnally-driven, with the risk decreasing after sunset Monday.
KEY MESSAGE 2, An anomalously strong upper level trough is forecast to develop over the Mid-Atlantic Region on Tuesday, with a potent shortwave diving southeast through Virginia and the Carolinas Tuesday into Tuesday night. A strong LLJ ahead of this feature should lead to increasing moisture advection, with PWATs once again climbing back above 2". Meanwhile, heating of a moist boundary layer should support moderate instability, with MLCAPE rising into the 1000-1500j/kg range. Aloft, a notable upper jet max is forecast to overspread the instability axis, supporting deep layer shear of 30- 45kt. While instability will be moderate, the shear/instability combo is notable for this time of year, as is the amount of lift expected.
Synoptically, the combination of all of the factors above checks a lot of boxes for severe weather potential. This also has overwhelming support from ensemble, analog, and machine learning guidance. The main potential limiting factor is timing. Recent guidance suggests convection may not reach ENC until after sunset. Despite the potential for a gradually stabilizing boundary layer, the strong large-scale forcing should help support deep convection well past the typical diurnal max in convective intensity this time of year. Given the amount of forcing present, it appears likely that an MCS will move through ENC during the evening and early overnight hours posing a risk of damaging winds. Low-level SRH around 100m2/s2 may support a few rotating updrafts capable of hail and perhaps a brief tornado. However, those latter 2 hazards should be lower compared to the wind risk. Lastly, while a MCS would be more progressive, the high PWAT airmass should support heavy rainfall rates which may support a short-fused flooding risk, especially for the area hardest hit the past few days (ie. Hyde County east through the Outer Banks).
Ahead of the convection, hot and humid conditions are expected, with heat indices rising to 100-105 degrees. This appears to be a bit marginal for heat headlines, but is something we'll continue to assess in later forecasts.
00z Monday through Friday Diurnal strato cu will dissipate this evening. Still some signal for MVFR stratus late tonight, though confidence low attm due to some convective debris clouds making into ENC late this evening. Confidence in this is low, therefore only a TEMPO for this possibility for PGV only.
The risk of SHRA or TSRA is expected to remain low through tonight as some weakening convection moves southward out of VA (06z-10z), however will leave in the PROB30 mention for TSRA for only KISO and KPGV. On Monday, increasing moisture and instability should lead to vcts for most TAF sites after around 18Z, though covg not high enough attm to warrant a TEMPO group for thunder this far out.
Outlook (Monday night through Friday): A notably strong storm system for this time of year is forecast to impact the area later Tue. This system will be accompanied by gusty winds and an increased risk of TSRA Tue evening, some potentially severe. Sub- VFR conditions are expected to accompany the TSRA risk. The strongest storms will be capable of 40-50kt winds and small hail. Much drier behind the fropa for Wed into the end of the week as high pres rebuilds.
Light north winds of 5-15kt will become southerly by tonight, but will remain light. For the coastal waters, a southeasterly long- period swell of 2-4ft at 8s is expected to persist through Monday night. A low-end thunderstorm risk is possible late tonight, mainly around the Albemarle Sound vicinity. On Monday, the thunderstorm risk should expand to include more of the inland rivers and sounds.
Outlook: A strong storm system for this time of year is forecast to impact area waters Tuesday into Wednesday with building winds and seas and an increased risk of thunderstorms. Winds of 15-30kt are expected late Tuesday into early Wednesday morning. Seas are forecast to peak in the 4-8ft range. Of note, a cluster of thunderstorms moving through Tuesday evening and Tuesday night will be capable of 40-50kt winds and hail.
Nc, beach hazards statement until 8 pm EDT this evening for ncz203. Marine, none.
