Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 201656 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 1156 AM EST Mon Nov 20 2017 .SYNOPSIS... High pressure will prevail through tonight. A weak trough will develop just off the coast and a cold front will approach from the northwest Tuesday. The front will pass off the coast early Wednesday followed by an area of weak high pressure. Low pressure with origins over the eastern Gulf of Mexico may bring rain to the area Wednesday night through Thanksgiving Day. The low will accelerate northeast away from the region by Friday with high pressure expected by the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 1020 AM Monday...Dry surface high pressure is in place across the Carolinas this morning. In addition, water vapor imagery shows a large swath of dry air aloft, resulting a precipitable water less than 0.2 inches as noted in adjacent 1200 UTC RAOBs. Low-level thickness scheme with full insolation yields high temperatures in the upper 50s to around 60. Radiational cooling should be optimum under clear skies and calm winds this evening; however, moisture is shown to increase from the Gulf coast in the 500-300 mb layer which could limit radiational cooling late. For now plan to remain cooler than MAV guidance for lows tonight. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 300 AM Monday...Tuesday is shaping up to be okay during the daytime with some clouds increasing with mild moist air overriding the cool dome of air across the ILM CWA. The dividing line is an inverted sfc trof that develops and lies across the Atlantic waters parallel to the ILM CWA coast. Models to some degree push this sfc inverted trof onshore and inland. However, I`m not entirely bought on the push well inland. I could see the trof moving just onshore but this is not the normal setup for the aka coastal trof to push well inland let alone onshore. As a result, will indicate the temp fcst with regard to just an onshore push. As for pcpn, have also knocked down POPs to a degree with a decent gradient from low chance well inland to good chance or possibly likely along the immediate coast and adjacent Atl Waters. The overall instigator for pcpn across the FA is mid-level shortwave troughs that push off the Mexican and southern Texas coasts respectively and into the Gulf of Mexico where it picks up moisture before crossing Central Florida during Tuesday. The shortwaves then accelerate northeastward Tuesday night along the coastal trough and by Wednesday daybreak they are off Cape Hatteras. This will supply additional dynamics other than the weak overrunning pcpn already in place by the time it`s affects commence. With stratiform type rains fcst west of the coastal trough, qpf will be on the low side with the highest occurring in the vicinity and east of the coastal trof where isolated heavier showers with possible thunder to occur. Have lowered temps for Tue from the previous fcst due to betting on the coastal trof not pushing well inland. For Wednesday... A cold front will push across first thing in the morning, helping to drive what`s left of clouds and pcpn further offshore. The front will stall well offshore but extend back inland across Florida. We then do it all over again, with overrunning type clouds late Wed thru Wed night with stratiform rains breaking out late in this time period, with the hier pops along the immediate coast and southernmost portions. Other than weak embedded southern stream s/w trofs, a rather decent northern stream 5H s/w trof dives southeastward from the upper Midwest and by early Thu, models indicate it may close off over Ga. This may draw back westward the stalled offshore front but still remaining offshore. A POP gradient will again occur across the area late wed night into Thu, with lowest well inland and highest along and east of the ILM CWA Coast. Enhancement to the QPF will come from weak embedded mid-level southern stream s/w troughs engaged with the stalled offshore front. The main QPF enhancement and higher POPs will come from the northern stream s/w trof and possible sfc low development on the stalled front offshore late in this period. For Wednesday temps, stayed on the lower side of Mos Guidance due to clouds and pcpn threat via the GFS, whereas the much drier European model this time frame has Wed max temps approaching 70 across portions of the FA. && .LONG TERM /THURSDAY THROUGH SUNDAY/... As of 300 PM Saturday...Lingering rain is possible early Wednesday as an upper trough moves out and a cold front moves out to sea. Another short wave trough could spawn low pressure development along the old front off the southeast U.S. coast. This will bring another chance of rain to the area Wednesday night into Friday, though the exact details of this scenario are still in doubt. Dry weather is expected for the remainder of the long term but light showers are possible with another frontal passage and vigorous upper trough on Sunday. Temperatures will be near seasonal normals of mid 60s Wed before falling back into the mid to upper 50s for Thu and Fri. Slightly warmer temperatures are expected Sat and Sun with highs in lower 60s. Mins temperatures Wednesday night will fall to the upper 30s to lower 40s with higher numbers SE and along the immediate coast. Temperatures in the mid 30s to around 40 are expected Thu night and Friday night before rebounding to the mid to upper 40s Saturday night. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... As of 18Z...VFR conditions and light winds will continue through this afternoon and tonight as high pressure moves overhead, then offshore late. Southerly winds developing above the surface will begin to bring in Atlantic moisture in the form of stratocumulus clouds with bases 3500-4000 feet AGL Tuesday morning between 14-16Z. Extended Outlook...MVFR conditions may develop in low clouds and light rain Tuesday night through Wednesday morning, then MVFR to IFR conditions are possible late Friday into Saturday in low clouds and rain. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 1020 AM Monday...High pressure across the Carolinas will maintain Northerly flow across the waters, generally around 15 knots or less. The flow will turn northeasterly during the day and diminish as the pressure gradient weakens across the coastal waters. The center of high pressure will move east of the Outer Banks tonight allowing the wind to further veer to an easterly direction. A weak coastal trough is expected to develop late, which would prevent complete return flow from developing west of the Gulf Stream. SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 300 AM Monday...Will see a roller coaster ride with respect to the wind direction fcst Tue into early Wed. This a result of an inverted sfc trof aka coastal front, that develops parallel to the ILM CWA Coastline and tries to push partially onshore. The sfc pg thru early Wed will be on the somewhat relaxed side with 10 to occasional 15 kt wind speeds possible. A cold front pushes off the coast and stalls well offshore, again parallel to the ILM CWA Coast during Wed. This front is pulled back toward the west Wed night but remains east of the local waters. With the sfc pg tightening especially late Wed and Wed night, NE winds 10-15 kt will increase to 15 to 20 kt with gusts to 25 kt possible Wed night as a sfc low develops along the stalled front offshore. Significant seas Tue into Tue night will run 2 to 3 ft with possible 4 footers. By late Wed and Wed night, sig. seas will build to 3 to 5 ft thruout with 6 footers remaining possible. At least SCEC thresholds will be met with SCA conditions still a possibility Wed night. LONG TERM /THURSDAY THROUGH FRIDAY/... As of 300 PM Saturday...N to NE winds INVOF 15 KT are expected through much of the period though a peak of 15 to 20 KT is possible Thu night into Friday. On the open waters, seas of 3 to 5 feet are expected through the period. Depending on low pressure development off the SE U.S. coast, conditions in this period could be hazardous and it is possible that winds and seas could exceed thresholds for Small Craft Advisories, 25 KT winds and/or seas of 6 FT, during this period. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...DCH NEAR TERM...JDW SHORT TERM...DCH LONG TERM...RAN AVIATION...TRA is the U.S. government's official web portal to all federal, state and local government web resources and services.