Area Forecast Discussion
Issued by NWS Wilmington, NC

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993 FXUS62 KILM 230219 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 1019 PM EDT Mon May 22 2017 .SYNOPSIS... Waves of low pressure will develop along stalled cold front producing increased chance of showers and thunderstorms through mid week. A cold front trailing from a deep low pressure system over the Ohio Valley on Thursday will push through bringing the final round of storms to the area. High pressure will build in on Friday maintaining quieter weather for much of the weekend. && .NEAR TERM /THROUGH TUESDAY/... As of 1000 PM Monday...Widespread thunderstorm activity over the past 6-8 hours has left a chaotic low-level wind and pressure pattern across the eastern Carolinas. A synoptic front is stalled back in the NC and GA mountains, while here closer to the coast a convective outflow boundary has sunk to a position 10-20 miles off the coast of Cape Fear, Myrtle Beach and Georgetown, SC. Synoptic south-southwesterly wind should overwhelm this boundary over the next 3-4 hours, with the current northerly winds observed along the coast and offshore veering back to the south again late tonight. Aloft, conditions are warm and very moist with deep southwesterly flow advecting rich Gulf moisture overhead. Precipitable water values are approaching 2.00 inches, and the 00Z Charleston, SC weather balloon revealed a potential warm-cloud layer nearly 12,000 feet deep. The depth of saturated above-freezing atmosphere has been shown to be an excellent predictor of heavy rain potential. Our first big wave of convection dropped a widespread 0.5 to 1.0 inch of rain across all but the immediate coast, with some embedded spots where radar and MRMS multi-sensor estimates are as large as 4.6 inches. A second wave of showers and t-storms currently across eastern Georgia should move up the coast overnight bringing another round of good rain. With plenty of elevated instability lingering overnight (500-1000 J/kg) forecast PoPs remain 80-100 percent with an additional 0.3 inches of rain inland and up to 1+ inch along the coast expected. && .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 300 PM Monday...Front remains stalled in the area Tue night, moving a little closer to the coast by Wed morning. Although moisture will be on the high side there will be a lack of upward motion. In fact there may be a lull as the passage of a surface wave Tue evening and its associated shortwave will lead to a period of subsidence Tue night. Forecast soundings depict this rather well showing a mid level subsidence inversion developing and precipitable water values dropping close by as much as 0.50 inch overnight. Mid level trough axis remains well west of the area Wed which will keep the front lingering in the region. Passage of the surface wave Tue night may briefly push the front south of the area early Wed but it is quick to return north as a warm front around midday Wed. Better rainfall chances develop later Wed and Wed night as potent shortwave dropping into the 5h trough early Wed helps kick the mid level pattern in motion. The 5h trough rotates east-northeast Wed into Wed night, driving a stronger cold front into the region Wed night. Increasing southwest flow ahead of the front, as well as strengthening low level jet, increases deep moisture in the region. Pwats rise to near 2 inches Wed afternoon and evening and mid level lapse rates steepen. PVA ahead of advancing shortwave, strong divergence aloft, and the abundance of moisture coupled with low level dynamics should yield a healthy line of convection Wed afternoon and evening. Although severe parameters are not particularly high there will be at least some potential for severe weather given the strengthening low level jet and modest shear. Large dry slot sweeps in late Wed night as the trough axis moves east, ending any precip prior to daybreak Thu. Cold front likely to be moving into the region as the period ends so cooler and drier air will not arrive until after the end of the period. High temperatures will continue running below climo with lows above to well above climo due to clouds and moisture. && .LONG TERM /THURSDAY THROUGH MONDAY/... As of 300 PM Monday...Deep frontal moisture to be offshore by the start of the period. However the main trough axis and strongest shortwave will be crossing the area and this should manage to squeeze a few light and short-lived showers. Continued dry advection and the lifting of the trough Thursday night should keep us dry despite one last final and moderately strong vorticity center streaking by. Zonal flow will keep the weekend dry and fairly seasonable with only gradually increasing surface dewpoints. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... As of 00Z Tuesday...A cluster of heavy thunderstorms just west of Myrtle Beach is merging into a line of showers and embedded storms stretching across the Wilmington area. This will create a massive problem for aircraft operations in the ILM area for the next several hours with prevailing IFR visibilities continuing until this thunderstorm cluster pushes offshore. Elsewhere, mainly light rain falling from mid-level clouds aloft should prevail through the evening hours with temporary heavier convective showers potentially developing at times. Cloud ceilings should lower to the MVFR/IFR category late tonight as surface temperatures cool. Scattered showers may linger all night, with scattered thunderstorms redeveloping Tuesday during the heat of the day. Extended Outlook...Reduced flight categories will be possible in periodic showers and thunderstorms through Thursday. The strongest convective activity should occur Wednesday. && .MARINE... NEAR TERM /THROUGH TUESDAY/... As of 1000 PM Monday...Showers and thunderstorms did indeed move out across the coastal waters this evening. The rush of cool northerly winds along the front edge of these storms has acted like a miniature cold front and has reached 10-20 miles from shore. This boundary should stall over the next couple hours, then should get overwhelmed by the synoptic southwesterly wind overnight. Winds should increase to SW 10-15 knots by 2-3 AM with gusts to 20 knots possible along the South Carolina coastal waters late. Another wave of showers and thunderstorms currently observed across eastern Georgia should move north along the coast overnight, bring more rough conditions for mariners from Georgetown through Myrtle Beach and Cape Fear. Reduced visibility in heavy rainfall and frequent lightning may redevelop late tonight. Seas currently 2-3 feet consist of a mix of 9-second swell and 4-5 second wind waves. Sea heights may drop half a foot or so in the next couple of hours, but should begin to build back up late tonight in the increasing southwesterly wind. SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 300 PM Monday...Front remains west of the waters through the period, maintaining southwest flow. Speeds start to increase later Wed and Wed night as the front moves to the coast and slowly strengthening low moving into the OH valley helps tighten the gradient. Southwest flow on the high end of the 15 to 20 kt range Tue night will increase to a solid 20 kt around midday Wed with 20 to 25 kt expected late Wed and Wed night, likely requiring SCA headlines for all waters. Seas will build due to prolonged and increasing southwest flow. Seas 4 to 5 ft at the start of the period will build to 4 to 6 ft during Wed, eventually reaching 7 ft Wed night. LONG TERM /THURSDAY THROUGH SATURDAY/... As of 300 PM Monday...Small Craft Advisory will be in effect on Thursday just ahead of a cold front that will pinch the gradient. Within the agitated wind field of the pinched gradient a strong upper disturbance will traverse the area possibly to enhance wind gusts. In the wake of this boundary there will be west winds to round out the period of gradually diminishing speed. Wave heights will similarly abate somewhat slowly. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...Beach Hazards Statement from 7 AM EDT Tuesday through Tuesday evening for SCZ054-056. NC...Beach Hazards Statement from 7 AM EDT Tuesday through Tuesday evening for NCZ106-108. MARINE...None. && $$ SYNOPSIS...RGZ NEAR TERM...TRA SHORT TERM...III LONG TERM...MBB AVIATION...TRA

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