884 FXUS62 KMHX 042021 AFDMHX Area Forecast Discussion National Weather Service Newport/Morehead City NC 421 PM EDT Tue Apr 4 2023 .SYNOPSIS... A weak surface trough will push off the Outer Banks as high pressure reestablishes offshore tonight through Thursday. A slow moving cold front will then push through the region Thursday night, and stall just to the south Friday and into the weekend with an extended period of unsettled weather possible. && .NEAR TERM /THROUGH TONIGHT/... As of 130 PM Tuesday...A fairly well defined, but weak, low-mid level low is centered over the Pamlico Sound, and is drifting slowly northeast. On the southeast flank of the low, convection is ongoing associated with weak large-scale forcing and where low-level convergence is maximized along a north-south surface (SFC) trough. The weak low will continue to drift northeast along the Eastern NC (ENC) coastline through this evening, but will gradually weaken as mid-level height rises overspread the area. Widespread low clouds in cyclonic flow around the low will continue to plague ENC for several more hours, but subtle westerly flow on the backside of the low will bring drier air aloft into ENC, with a gradual mixing out of the mostly cloudy conditions. I don't think we'll completely lose the clouds, though, especially with diabatic heating of the moist boundary layer. The heating of the moist boundary layer will also support weak, diurnally-driven destabilization, but warming temps aloft will lead to a strengthening cap developing. This combined with nebulous forcing over land should prevent additional afternoon showers or thunderstorms from developing, even with the potential of an afternoon seabreeze. Weak southerly flow will keep the boundary layer moist, with dewpoints possibly even rising through the night. Light winds, a moist boundary layer, and a preconditioned environment (ie. rainfall over the past 12-24 hrs) appears to be supportive of an increased risk of low clouds and fog tonight. The previous forecast nicely opened the door to this potential and, if anything, I opened it even further. It looks like a scenario where fog initially will develop over/near the coastal waters, then advect/develop inland. How far inland the fog threat reaches is less certain, but along the coast, a period of dense fog appears plausible. Increasing clouds and the light southerly flow will keep temps very mild tonight. && .SHORT TERM /WEDNESDAY/... As of 145 PM Tuesday...The primary forecast challenge Wednesday will be how quickly morning fog/stratus mix out. There's even the potential that low clouds and fog will last longer than currently advertised. The setup Wednesday doesn't appear supportive of a rapid mixing out of the fog and stratus, so I opted to slow the clearing of clouds. Consequently, this also slows the diurnal rise in temps. For this reason, I went below the previous forecast and lowered highs a few degrees Wednesday. This is especially the case along the coast where the greatest potential exists for low clouds and fog to last the longest. If clouds last longer than forecast, highs tomorrow will end up lower than what I currently have in the forecast. The other forecast challenge is a westward-drifting coastal trough (remnants of today's weak low/trough). An increasing low-level flow should begin to pull that feature back towards the coast, and may provide sufficient lift for showers across our central Outer Banks areas (Ocracoke/Hatteras). The thunderstorm risk looks to remain offshore, though. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... As of 335 AM Tue...Dry and very warm weather returns midweek before the next system impacts the region late Thursday in the form of a cold front, which will stall just to our south for the weekend and bring an extended period of unsettled conditions. Thursday and Friday...00z suite of guidance has come into better agreement in regards to a cold front approaching the Carolinas late Thursday and crossing on Friday before stalling to our south. Apart from a few offshore showers, most of Thursday appears dry with shower activity likely not reaching our FA until nightfall (the NAM is a slow outlier, keeping conditions dry until daybreak on Friday). There will be some lingering instability to work with, mainly across the coastal plain and farther inland thanks to robust heating earlier in the day, and a few thunderstorms are probable across the coastal plain. Effective shear will be lacking as best kinematics will be displaced much farther to the north, and severe risk appears minimal. Model differences become apparent again on Friday with disagreements of how far south the front makes it before stalling, with the ECMWF taking the front farther south across the Gulf States while the GFS keeps it closer to the Carolinas. Maintained high-end chance PoPs for the period but opted to hold off on likely PoPs for now given the uncertainty. With high pressure wedging into the region from the north resulting in a classic CAD pattern, guidance is likely too bullish on high temperatures and lowered forecast highs well into the 50s, on the low end of guidance. Saturday through Monday...Model divergence increases further for the weekend, although solutions continue to paint an unsettled picture. Focus turns to the Saturday/Sunday time frame as a southern stream shortwave pushes across the southeastern CONUS, driving a wave of low pressure and enhanced precipitation along the stalled frontal boundary. Again, where this precip ends up is dependent on the placement of the front but using a blend of all model solutions areas from New Bern south appear to be the best candidates for seeing appreciable rainfall (up to an inch or more storm total QPF) and increased PoPs to likely in this corridor. Temperatures for Saturday follow the same trend as Friday, on the lower end of guidance with highs in the 50s. General NBM was favored beyond Sunday given model differences, although a signal for drier conditions is evident behind the weekend system. && .AVIATION /20Z TUESDAY THROUGH SUNDAY/... SHORT TERM /Through Wednesday Morning/... As of 145 PM Tuesday... * Widespread IFR/LIFR conditions likely tonight (50-70% chance) A weak area of low pressure will slowly move through the Outer Banks through this evening, eventually weakening into a coastal trough by tonight. A moist cyclonic flow around the low will continue to support low CIGs (MVFR/low VFR) this afternoon, but a gradual scattering out of the CIGs appears likely by late this afternoon. This will be short-lived, though, as low CIGs and BR/FG attempt to redevelop. The signal for FG looks pretty good from a pattern recognition and model standpoint. Therefore, I hit this potential a bit harder in the TAFs compared to the previous forecast. From a probabilistic standpoint, the highest risk of LIFR conditions will be from OAJ to EWN, and points south. Further inland, the potential for LIFR conditions exists, but confidence is lower, so I went more conservative with the TAFs for now. The challenge on Wednesday will be figuring out how quickly the low CIGs and VIS mix out. Model guidance have a tendency to be too quick to mix out low CIGs in these scenarios, so I trended slower with the departure of IFR/LIFR conditions. Along the Crystal Coast, conditions may remain LIFR/IFR into the mid to late morning hours. Lastly, the above-mentioned coastal trough will attempt to move west during the day Wednesday, and could bring a few SHRA to the central Outer Banks (vicinity of KHSE). LONG TERM /Wednesday through Saturday/... As of 340 AM Tue...Improved flight conditions expected much of Thursday, before an approaching cold front brings scattered showers and thunderstorms across the coastal plain terminals in the late evening and overnight hours. Front stalls just to our south on Friday with scattered rainfall and low clouds likely, resulting in a potentially extended period of MVFR to IFR conditions. Stronger system may impact the region on Saturday, bringing more widespread IFR conditions to all terminals. && .MARINE... SHORT TERM /Through Wednesday/... As of 400 PM Tuesday...A weak area of low pressure is currently centered over the Pamlico Sound this afternoon. This low will continue to weaken and move slowly northeast out over the northern coastal waters by this evening, leaving behind a residual coastal trough oriented north to south. Southeast of the low, southerly winds have been gusting as high as 20-25kt at times, mainly over the central and northern waters. This has also allowed seas to build to 4-5 ft. These conditions will continue into this evening, but seas and winds will begin to lay down tonight as the low weakens. The residual coastal trough will then be a focus for showers and a few thunderstorms tonight into Wednesday, mainly impacting the central waters. West of the trough, a light southerly flow will bring increasing moisture into the area, with a favorable setup for sea fog. If confidence remains high, a Marine Dense Fog Advisory may eventually be needed. LONG TERM /Wednesday through Saturday/... As of 345 AM Tue...Quiet marine conditions anticipated until Thursday night into Friday as a cold front approaches and crosses the waters, stalling to our south. Wednesday, southerly flow continues over the waters with highest winds, around 15 kt, over the Gulf Stream. As front nears on Thursday, tightened pressure gradient will nudge winds slightly higher, up to 15-20 kt for both offshore and soundside zones. Throughout the period, seas should be no higher than 3-5 feet. Behind the front, an extended period of northeasterly winds at 20-25 kt with higher gusts, lasting from Friday morning through Sunday, will bring likely SCA conditions for all offshore waters and the Pamlico Sound, extending into the weekend. Given the persistent and strong fetch, seas are likely to become dangerous particularly late in the weekend with highs of 10-15 feet over the Gulf Stream and 8- 10 foot seas for the waters north of Hatteras as well as Raleigh Bay. && .MHX WATCHES/WARNINGS/ADVISORIES... NC...None. MARINE...None. && $$ SYNOPSIS...MHX NEAR TERM...RM SHORT TERM...RM LONG TERM...MS AVIATION...RM/MS MARINE...RM/MS