Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 260814 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 314 AM EST Sun Feb 26 2017 .SYNOPSIS... Much cooler temperatures expected today as high pressure builds into the Carolinas. These cool temperatures will be short lived as a warm front lifts north early Tuesday. Near record high temperatures expected again by the middle of the week before a cold front crosses the area on Thursday. A return to winter like temperatures is expected for next weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 3 AM Sunday...Last night`s cold front is now well offshore, with breezy northwesterly winds blowing across the eastern Carolinas. One interesting effect none of the models were intense enough with was the sudden drop in dewpoints as the front blew through. Dewpoints dropped 20-30 degrees in less than an hour at most stations! Water vapor satellite imagery showed bands of very warm brightness temperatures coincident with the drop in dewpoints, perhaps implying strong downward motion entraining dry mid-level air into the well-mixed boundary layer in the post-frontal cold advection. Surface high pressure over Tennessee this morning will work its way to the Carolina coastal plain by late afternoon. The airmass is quite a bit cooler than yesterday and even with full sunshine highs are only expected to reach 60 degrees. With the high nearly overhead and a dry airmass in place, temperatures should fall quickly after sunset. Return flow behind the departing high will occur too late to disturb a strong nocturnal inversion, and lows should fall into the 30s all the way down to the coast. I strongly favor the colder NAM MOS number over the GFS tonight. Lows of 29-32 are expected across the typically cold pocosins (peat soils) of southeastern North Carolina and would trigger freeze warnings if this were a little farther into spring and the growing season had begun. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 3 AM Sunday...High pressure will move farther away from the U.S. east coast Monday and Tuesday, opening up the door for subtropical warmth and humidity to return to the Carolinas. The modification will begin Monday morning as the nocturnal inversion breaks and southeasterly winds develop. Highs Monday should reach the lower 70s inland with mid to upper 60s near the beaches. The forecast has shifted somewhat for Monday night compared to 24 hours ago. While an approaching upper disturbance and low-level warm advection should still work together to develop a large zone of weak to moderate isentropic lift across the Carolinas, the quality of moisture in the incoming southerly flow is not quite as good in the current 00z model runs. In particular, large swaths of dry air at 5000-12000 ft AGL will act to reduce the areal coverage of rainfall. The isentropic lift itself will proceed much as the models showed 24 hours ago, but without nearly as much moisture being lifted and cooled to its dewpoint, the risk of rainfall has diminished. PoPs in the 30-40 percent range are currently forecast for Monday night (mainly after midnight) with lows in the mid to upper 50s. By Tuesday the same airmass we had yesterday will be back, only with higher dewpoints given its source region in the southern Bahamas. Highs could approach 80 in a few inland spots with 70s expected for all but the beaches. Surface-based instability should grow to 500- 1000 J/kg with bulk shear values increasing toward 40 kt by late afternoon. Lapse rates aloft are not that bad, and given rather low wet-bulb zero heights around 9500 feet I would not be surprised for some sort of hail threat to develop in thunderstorms. Waning instability during the evening should end the thunderstorm threat. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 3 AM Sunday...Forecast area will be solidly in the warm sector Wed with temperatures approaching 20 degrees above normal. Convection will be possible Wed afternoon given low level moisture and diurnal heating, but there will be several limiting factors. Mid level subsidence and dry air above 850 mb will be the biggest issue, but there is also a lack of forcing. A modified sea breeze may lead to some storm development across southeast NC but confidence is low. Better precip chances will be late Wed night through early Thu as strong cold front moves across the area. Frontal passage occurs Thu morning, coincident with the surface based instability minimum. However, the front and its 5h trough will provide strong lift and a healthy chance of showers and isolated thunderstorms through the first part of Thu morning. Strong cold advection develops Thu with 850 temps dropping around 10C from Thu morning to Thu evening. Highs Thu will end up well above climo, but will likely occur during the first few hours of the morning with temps steadily trending down during the day. Incoming air mass is very dry with potential for RH dipping below 30%. Temps below climo Fri and Sat with a reinforcing shot of cold air expected Fri night into Sat. && .AVIATION /08Z SUNDAY THROUGH THURSDAY/... As of 06Z...VFR conditions are expected throughout the TAF period. NW winds invof 10 KT will become northerly after sunrise before becoming light and variable after sunset this evening. Extended Outlook...VFR. VSBY and ceilings lowered to MVFR/IFR with pcp Mon night into Tues and again with SHWRs on Wed. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 3 AM Sunday...The cold front blasted offshore Saturday evening with breezy northwest winds blowing all night. High pressure over Tennessee will move eastward today, reaching the coastal Carolinas this evening then moving offshore overnight. Northwest winds will diminish in speed today, becoming light and variable this evening, then turning easterly late tonight. The Small Craft Advisory will come down shortly for the South Carolina waters but will run through mid-morning for the North Carolina waters where residual 6-foot seas will likely continue. SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 3 AM Sunday...High pressure east of the Outer Banks Monday morning will move farther offshore Monday night and Tuesday. Southeasterly winds Monday should turn southerly by Tuesday in the flow between the departing high and low pressure advancing eastward across the Plains states. LONG TERM /WEDNESDAY THROUGH THURSDAY/... As of 3 AM Sunday...Southwest flow will steadily increase Wed, peaking at 20 to 25 kt in the afternoon and evening ahead of cold front approaching from the west. Front moves east across the waters Thu morning with offshore flow developing by midday. Gradient and cold advection will keep offshore flow a solid 15 kt into Thu evening before northerly winds start to weaken. Seas 3 to 4 ft Wed morning will build to 4 to 7 ft Wed evening and remain above SCA thresholds through much of Thu morning before offshore flow drops seas to 3 to 5 ft Thu afternoon and 2 to 3 ft Thu night. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...Small Craft Advisory until 3 AM EST early this morning for AMZ252-254-256. Small Craft Advisory until 10 AM EST this morning for AMZ250. && $$ NEAR TERM...TRA SHORT TERM...TRA LONG TERM...III AVIATION...TRA

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