Key MESSAGE 1, Latest surface analysis depicts a stalled frontal boundary stalled over Onslow Bay with multiple weak waves of low pressure migrating along the boundary. The passing lows will be a focal point for developing showers and a few thunderstorms today, with a shower threat mainly south of US 70 in the morning and then an iso to sct thunderstorm threat in the afternoon as a stronger low lifts northward and pulls the stalled boundary towards the NC/VA border late. Morning shower threat looks very marginal with forecast soundings depicting considerably dry sub-cloud layers, hinting that the day may start overcast with plenty of virga and only some spotty rainfall. Thunderstorm development, associated with convergence ahead of the surface low, is of higher confidence and favors areas along and east of NC17. Sct shower threat lingers overnight into Wed morning with a quick moving surface trough transiting the region ahead of a passing mid-level shortwave.
The next best chance for stronger storms remains Thursday night into Friday ahead of a stronger front where deeper shear will likely be present along with strong instability as temperatures soar back into the 90s and humidity remains oppressive. Like previous days, better kinematics and thus higher risk of organized convection will likely be to our north in the Mid- Atlantic. Medium- range AI NWP guidance still highlights much of the Carolinas for a severe risk during this period. The primary threat risk is damaging winds, but other hazards remain on the table.
KEY MESSAGE 2, Relatively cooler temperatures will prevail again today with more overcast skies and ENC on the cool side of the frontal boundary. This reprieve will end tomorrow as the boundary lifts northward tonight into Wednesday. As alluded earlier, increasing southwesterly flow ahead of the late-week front will boost low- level thicknesses and kick temperatures into the mid to upper 90s by Thursday. Paired with Tds in the low to mid 70s, heat indices will climb back to around 105+. The passing front may cool things down briefly for the weekend, but medium range guidance suggests excessive heat will remain a concern starting next week.
06z Tuesday through Saturday VFR conditions in place across all terminals this hour, although as forecast EWN and southeastern terminals have been flirting with a sct to bkn cloud deck for the past few hours. This will likely continue through the overnight hours while cirri deck expands overhead ahead of approaching shortwave and weak developing surface low. This low will be the focus for a modest shower and iso thunderstorm threat, although evolution remains uncertain with plenty of spread in hi-res guidance. This is particularly true for the morning shower threat where more virga than measurable precipitation is likely given very dry sub-cloud layers. Higher confidence is in a thunderstorm threat, especially for terminals from EWN to the north and east with convergence ahead of the approaching surface low. Threat will be diurnal and all sites should be dry by 00z Wed.
Overnight Tues expected to be dry but with a returning and more widespread low stratus threat with increasing low-level moisture return.
Outlook: Iso shower and thunderstorm risk will extend into Wednesday. More widespread convective threat returns Thursday night and especially Friday with stronger front. Overnight fog and stratus threat possible each morning. Weekend is trending drier and more quiet with predominant VFR expected.
Regional observations show a stalled frontal boundary sitting over Onslow Bay, with easterly winds of 5-10 kt to its north and around 10 kt to its south. Main focus today will be a weak wave of low pressure migrating along the frontal boundary, pulling it north through the day and ushering in more predominant southwesterly winds after sunset. A brief but strong surge of winds is possible overnight for outer portions of Onslow Bay in the wake of the passing low, with SCA conditions possible beyond 20 nm. This will likely boost seas here briefly to around 6 feet. Elsewhere, seas will build up to 3-5 feet south of Cape Hatteras, 2-4 feet north.
Outlook (Wed through Sat): Periodic nocturnal and early morning risk of showers and thunderstorms is possible each weeknight, although most likely odds will be Thursday night into Friday ahead of stronger front approaching area waters. This front will also be the next focus of widespread SCA conditions with an increasing risk of Gales across the outer waters.
Nc, none. Marine, none.
