Area Forecast Discussion
Issued by NWS Wilmington, NC

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616 FXUS62 KILM 200926 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 426 AM EST Mon Nov 20 2017 .SYNOPSIS... High pressure and tranquil weather will control the local weather through tonight. A coastal trough just off the Carolina coasts and an approaching cold front from the northwest will combine to produce stratiform light rains late Tuesday and Tuesday night ending with the cold frontal passage early Wednesday. Weak high pressure will follow on Wednesday. Low pressure with origins over the eastern Gulf of Mexico during the mid week period, may bring unsettled weather to the local area in the form of stratiform rains late Wednesday night thru ThanksGiving Day Thursday. The low will accelerate northeast away from the region by Friday with modest high pressure slated for the upcoming weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 300 AM Monday...Quiet and cool early this morning as large area of high pressure centered near the MS VLY ridges eastward. Beneath this expanding ridge, light north winds continue locally driving weak CAA and temps dropping into the 30s in many locations, with a few isolated readings near freezing. A frost advisory remains in effect for much of the inland zones not already done with their growing season, and have added areas of frost to these zones. Temps will remain a bit warmer than last night so frost should not be as widespread as Sunday morning, but many locations will likely wake up to frost around sunrise. Thereafter, a sunny but cool day is forecast as the aforementioned high swings eastward to become overhead this evening. Weak CAA will shut off, but a very shallow cold dome topped by a subsidence inversion above 900mb will keep temps below 60 for highs today in most areas, with a few low 60s possible in the far southern zones. This high will shift offshore in response to a trough digging into the Gulf of Mexico, and this will cause surface winds to shift to an onshore direction tonight. The forecast begins to diverge at this point due to the development of a coastal trough, with the NAM the fastest and strongest with the sharpening of this feature. For now have sided with the slower/less robust GFS/ECM/CMC and keep the area dry with increasing cirrus but little in the way of low cloud cover through Tuesday morning. Light easterly winds and increasing sky cover will keep mins a bit warmer tonight, around 40 at the coast and mid 30s well inland. The forecast profiles are quite dry inland so frost may have difficulty forming, but local frost tool did produce some patchy frost well inland so have left a mention in the forecast where temps fall below 36. Do not anticipate the need for a frost advisory Monday night however. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 300 AM Monday...Tuesday is shaping up to be an "ok" 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 s/w trofs 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 s/ws then accelerate northeastward Tuesday night along the coastal trof 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 trof, qpf will be on the low side with the "hiest"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 1st 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. Atl Waters. 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 hiest along and east of the ILM CWA Coast. Enhancement to the QPF will come from weak embedded mid- level southern stream s/w trofs engaged with the stalled offshore front. The main QPF enhancement and hier 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 /10Z MONDAY THROUGH FRIDAY/... As of 06Z...High confidence in VFR through the valid period. High pressure will shift eastward today, moving atop the terminals this aftn and then offshore tonight. This occurs in conjunction with W/NW flow aloft creating nearly cloudless sky conditions and northerly winds of 10 kts or through the aftn. As the high shifts offshore winds will begin to shift to the east in response to a developing coastal trough, but at still light speeds. No low level clouds are expected within this valid period, but mid-level flow becoming SW will drive increasing cirrus level moisture and a BKN cirrus cig is forecast Monday night, but VFR will persist. Extended Outlook...MVFR conditions may develop in low clouds and light rain Tuesday through Wednesday morning, then MVFR to IFR conditions are possible Thursday night into Friday in low clouds, rain, and fog. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 300 AM Monday...High pressure currently across the MS VLY will shift eastward today, causing a slow decrease in wind speeds along with veering in direction. Current winds across the waters are from the north around 10 kts, still 15-20 kts near Frying Pan Shoals, but will ease through the morning as the gradient begins to relax thanks to the approach of the high pressure. Wind direction will become NE this aftn, then E, and finally SE tonight, with speeds primarily around 5-10 kts regardless of direction. A few 4 ft seas still lingering out there this morning will deamplify to around 2 ft all waters this evening and tonight, with a 4-5 sec wind wave following the mean wind the primary wave group. 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. Atleast 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...Frost Advisory until 9 AM EST this morning for SCZ017-023-024- 032-033-039-053. NC...Frost Advisory until 9 AM EST this morning for NCZ099. MARINE...None. && $$ SYNOPSIS...DCH NEAR TERM...JDW SHORT TERM...DCH LONG TERM...RAN AVIATION...JDW MARINE...

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