Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 191729 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 129 PM EDT Wed Apr 19 2017 .SYNOPSIS... A cold front stalled over South Carolina this morning will lift back north as a warm front today into tonight. The Bermuda High will expand west over the region Thursday through Saturday. Another cold front will move through Sunday night with high pressure building in behind it into early next week. && .NEAR TERM /THROUGH THURSDAY/...
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As of 130 PM Wednesday...Showers becoming quite widespread 15-45 miles inland from Cape Fear and also 10-25 miles inland from the South Carolina coast. This is on and just west of the seabreeze boundary. So far none of the convection is all that deep, however with CAPE building toward 1000 J/kg we could see some storm tops exceed 35000 feet in the next few hours. Slow cell motion is expected, and this could create pockets of locally heavy rain. Discussion from 930 AM follows... 1040 mb high pressure over the Canadian maritime provinces is ridging down the U.S. East Coast this morning. A weak stalled front near Savannah, GA marks the southern periphery of the high`s influence. Models show as the Canadian high begins to retreat later today the front should return northward slowly. The Canadian high has pushed some quite dry air southward and into the Carolinas. Dewpoints are in the mid 50s along the I-95 corridor. Dewpoints should recover into the lower 60s by mid to late afternoon as northerly winds veer easterly. Given breaks already observed in the low and mid level cloud cover, enough insolation should develop to push temperatures well into the 70s this afternoon. It`s rather chilly up at the 500 mb level, -14C on the 12Z MHX sounding, and surface-based CAPE should rise to around 1000 J/kg. Given broad low-level convergence in the vicinity of the front plus some added kick from a weak afternoon seabreeze, I have focused my afternoon PoPs along a corridor from Kingstree to Marion, Conway and Whiteville. PoPs as high as 50 percent are forecast in this area, with much lower potential at the beaches and immediate coast due to cooler, more stable air advecting onshore. Changes with this update mainly focused on dewpoints, afternoon PoPs, and adding some patchy fog late tonight.
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&& .SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/... As of 245 AM Wednesday...Low-end rain chances this period as the trend of mid-level drying is underway, and more in earnest late Thursday as H8-H7 trajectories turn more westerly. Low-level heating accompanied by dewpoints in the middle 60s will allow for a shower or TSTM to pop along any boundary or the afternoon sea breeze front Thursday. This is possible Friday except that more pronounced mid- level drying will suppress convective depth Friday and TSTMS were removed and limited to showers. 80s for maximums both days away from the coast and Friday should be a few degrees warmer than Thursday as warm air advection becomes slightly more of a player. POP values will take a bump upward late Friday as a decaying frontal boundary approaches the area. Minimums remain well above normal for late April elevated into into the lower and middle 60s aided by low-level jets each of the overnight periods. No severe weather signatures appear in the cards this period. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 300 PM Tuesday...A streak of very warm weather is expected Friday and Saturday before a significant rain/thunderstorm event accompanies a cold front early next week. A low amplitude upper ridge across the Southeast will support surface high pressure out near Bermuda on Friday and Saturday. Southwesterly low-level flow around this high should provide two warm days with highs easily reaching the upper 80s on Friday. Earlier models had suggested a backdoor cold front may slip southward into the area, but this appears to be a much lesser possibility now. I have increased forecast highs and lows Friday through Saturday by as much as 6 degrees in spots, and feel that I still may be too cool, especially inland on Saturday. Capping aloft with the ridge should keep diurnal thunderstorm activity in the isolated range, mainly inland of each day`s seabreeze front. Our weather pattern changes abruptly by Sunday as an impressive upper level system (especially for late April) dives into the southeastern quarter of the nation. Timing differences between the GFS and ECMWF has narrowed quite a bit with this morning`s 12z model run, and confidence is growing that a wave of thunderstorms will progress from west to east across the area late Sunday ahead of the surface cold front. A non-supercell severe risk may very well develop with this system as models are showing rather strong but unidirectional winds aloft coupled with a favorably positioned jet stream along the Mid-Atlantic and New England coast. As the mid and upper level system slows and almost cuts off along the GA/SC coast on Monday, steadier rains could linger through Monday and perhaps into Monday night along the coast. This is excellent news for especially South Carolina as "abnormally dry" and "moderate drought" designations are expanding on the latest U.S. Drought Monitor summary. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
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As of 18Z...Widespread shallow convective showers are ongoing just west of ILM, CRE, and MYR associated with this afternoon`s seabreeze circulation. This activity should remain just inland from these coastal airports with no direct impacts on the airfields themselves. Convection is drifting westward and could affect the FLO and LBT airports between 19-23Z. Once this activity weakens and dissipates with the loss of sunshine this evening, the next forecast problem is the potential for ground fog late tonight. Increasing low-level moisture and light winds should create at least tempo IFR conditions at most airports around the region overnight, probably developing between 05-07Z. Extended outlook...MVFR/IFR conditions possible in showers and TSTMS Saturday through Sunday night.
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&& .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 930 AM Wednesday...A weak front is stalled in the Savannah, GA vicinity this morning, but should begin to lift northward later today. The pressure gradient is rather weak along the South Carolina coast, but tightens up in the Cape Fear region where northeast winds are averaging 15 knots currently. Models suggest this region of stronger winds should die away this afternoon, with easterly winds around 10 knots expected to develop across the entire area. Showers well offshore this morning have been developing in an unstable environment fueled by heat from the Gulf Stream. As the inland Carolinas heat up later today showers and t-storms should develop there as well, hopefully leaving the coastal waters in a lull with no significant risk of rain today or tonight. SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 245 AM Wednesday...Marine conditions are manageable THU in developing SW flow but will become increasingly hostile THU night and FRI as a low pressure trough inland and high pressure offshore begin to more strongly interact. SW gusts to 25 KT FRI and FRi night may prompt a Small Craft Advisory or an Exercise Caution statement. Spectral plots show 3-4 foot SW waves every 4-5 sec will co-mingle with 2-3 foot E waves every 8-9 sec. An isolated TSTM is possible early THU and again late THU while FRI may be confined to a marine shower at best. LONG TERM /SATURDAY THROUGH SUNDAY/... As of 300 PM Tuesday...High pressure out near Bermuda will control our area`s weather through the end of the week, maintaining south- southwesterly winds and generally dry conditions. Compared to models a day or two ago, the high is now expected to be stronger and should deflect a backdoor cold front that was earlier believed to make it this far south. Wind speeds should average 15 knots on Friday and 10- 15 knots on Saturday. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS... NEAR TERM...TRA SHORT TERM...JDW LONG TERM...RGZ AVIATION...TRA

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