Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 240539 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 139 AM EDT Mon Jul 24 2017 .SYNOPSIS... A cold front will approach from the north tonight and Monday and may slip into the area mid week before stalling and then dissipating by Thursday. Showers and thunderstorms with heavy rain will increase in coverage Monday through Wednesday and this will serve to knock down the heat although the high humidity will remain. Drier air may briefly work into the area Thursday, but the arrival of a stronger cold front will bring more thunderstorms by the weekend. && .NEAR TERM /THROUGH TODAY/... As of 900 PM Sunday...Convection winding down across the FA and will indicate so in the updated forecast. By midnight, most areas should be dry with convective debris cloudiness overhead. These clouds will thin out with time as the overnight progresses. The immediate coast could get broad-brushed by convection toward daybreak and there-after as a mid-level trof over the Atlantic waters passes in close proximity. No changes to the overnight lows with mid to upper 70s, to around 80 at the coast. Previous.................................................... As of 230 PM Sunday...Many locations across the forecast area have reached a heat index of 105F or higher with afternoon temperatures in the lower to mid 90s and dewpoints in the mid to upper 70s. Convection along the sea breeze has been suppressed thus far. However, convection has fired far inland and a potential cold pool may drive a more organized area of convection southeastward from western NC. This feature would likely persist into the evening and affect part of the Pee Dee per the latest HRRR. At any rate, plan on focusing the highest POPs across the Pee Dee and Lumberton areas through the evening. SPC Mesoanalysis DCAPE plot shows a swath of >1000 j/kg across the Pee Dee and Lumberton areas. In addition, the CAPE has swelled to 4000-5000 j/kg and subsequently the Marginal severe weather risk area has been expanded to include all of northeast SC and southeast NC. The primary severe weather threat is from damaging wind gusts, while some of these storms may be prolific lightning producers as well. Southwesterly flow will continue to pump warm/moist air into the area through tonight with Bermuda High pressure in place. The mid- level subtropical ridge will continue to break down across the Carolinas as precipitable water values increase above 2 inches. This will open the door to increased coverage in showers and thunderstorms during Monday. The heat index will be tempered by increased cloud cover and increased coverage of storms during Monday. As a result a Heat Advisory is not planned for Monday at this time. Lastly, the new moon tides along with the persistent southwesterly fetch (likely holding up water in the Cape Fear River basin causing the half foot plus anomaly noted on the tide gauge) around the Bermuda High will lead to another round of minor coastal flooding at downtown Wilmington with high tide tonight. Plan to issue another Coastal Flood Advisory to account for the higher than normal water levels. && .SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/... As of 300 PM Sunday...Mid to upper trough will move from the Great Lakes to off the New England Coast through the period. This will push a cold front into the Carolinas by Mon eve and down into our forecast area by Tues morning and should end up lingering right through our local forecast area into Wed. It looks like the front will get strung out running from the Atlantic waters off the New England Coast down into the southeast perhaps running right along the NC/SC border. Moisture will pool ahead of this front with pcp water values up above 2 inches in deep SW flow along the coastal Carolinas. The trough aloft will run right down along the southeast coast and will need to follow exactly where the best upper dynamics will be to focus main convective activity through the period. The latest GFS shows our local area to be in a prime spot for enhanced activity through Tues while the ECMWF shows the best dynamics to run a little farther south. Either way, this lingering front and upper dynamics will produce plenty of clouds and convection around through the period. The sea breeze should act to hold front up or push it back inland with best convective activity likely along the coast early and farther inland in the aftn to eve. The clouds and pcp will keep temps down closer to normal... round 90 for highs, but a few spots with breaks of sunshine could spike up further. The humid air mass in place will combine with heat to push heat index values up around 100. Overnight lows will be in the mid 70s most places with slightly lower temps Tues night into early Wed as front drops south. Gusty SW winds ahead of front will lighten as boundary drops south into the area through Tues. As flow lightens, the potential for flooding will increase as storm movement will slow. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... As of 300 PM Sunday...The extended forecast period looks quite wet as the ridge builds across the southern & central Rockies and a trough remains across the East. This seems to be a trend this summer which has so far featured very regular rainfall and soil moisture values in the 70-90th percentile for the coastal Carolinas. Wet soils may also be part of the reason why we haven`t had any extreme heat so far. The highest temps measured as far this year include 95 in Lumberton and 96 in Florence. Both sites typically have hit 100 by this late in the summer. A potent upper disturbance over South Carolina on Wednesday will sit atop a stalled front and weak surface low pressure. Throw in precipitable water values over 2.0 inches and cold enough temperatures to support convection even with a cooler boundary layer and showers and thunderstorms with locally heavy rainfall appear likely. The GFS is faster than the ECMWF moving the system offshore Wed night and Thursday, and our forecast rainfall chances will linger into Thursday especially along the coast. Friday looks like the driest day of the bunch as we may be in between upper disturbances. Models are probably too warm with temperatures Friday, especially inland, given what should again be wet soil conditions after the Tuesday-Wednesday rainfall event. By Saturday and Sunday, the East Coast trough will deepen significantly as shortwaves dive into New England, the Great Lakes, and perhaps the Midwest too. A rather strong cold front for the middle of summer is shown on both the GFS and ECMWF to approach the Carolinas from the northwest on Sunday. This solution is overall slower than yesterday`s models showed. The ECMWF solution looks more plausible given little GFS/Canadian ensemble support for the 12Z operational GFS cutting off shortwave energy to our west on Sunday. && .AVIATION /06Z MONDAY THROUGH FRIDAY/... As of 06Z...Convective debris clouds linger over the area this morning with patches of marine stratus occasionally moving onshore. Gusty southerly winds along the coast are helping push MVFR and IFR stratus into the coastal terminals. Think IFR will be shorter duration and for now have kept MVFR as the dominant category. Expect VFR conditions today with another round of afternoon and evening showers and thunderstorms. Coverage will be similar to yesterday with inland sites having slightly better chances for afternoon storms but all terminals will have potential for brief periods of MVFR and IFR conditions with any storm. Loss of heating will once again bring a decrease in storm coverage and intensity. However, debris clouds left over from storms will linger through the end of the period, mainly as mid level cloud around 12k ft. Extended Outlook...Brief to occasional MVFR/IFR conditions from showers and thunderstorms Mon night thru Wed becoming isolated on Thu. && .MARINE... NEAR TERM /THROUGH MONDAY/... As of 915 PM Sunday...SCA has been raised for the ILM Waters from Surf City to Murrells Inlet. Tonight thru much of Monday... winds will run SW 15 to 25 kt and seas in the 4 to 6 ft range. South of Murrells Inlet...SCEC conditions to continue tonight into Monday under SW 15 to 20 kt sustained winds and significant seas in the 3 to 5 foot range. Will indicate few gusts up to 25 kt but if this occurrence increases then may have to upgrade to a small craft advisory. Significant seas will mainly be governed by the 4 to 6 second period locally produced wind driven waves. Previous...................................................... As of 230 PM Sunday...Persistent southwesterly fetch between inland trough and Bermuda High pressure will continue through the near term period. As a result, southwesterly winds will prevail in the 15 to 20 knot range with steep wave conditions at 4 to 5 ft, especially away from the coast (a little lower wave closer to the coast but just as choppy). Convection possible across the waters tonight and into Monday as the overall pattern begins to change. Will leave the Small Craft Should Exercise Caution as is spatially but carry it through Monday. SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... As of 300 PM Sunday...A cold front will drop south and east producing a tightened gradient flow as Bermuda High continues remain to our east. The trough inland will also get pushed east aiding to increased flow into Mon eve. Overall expect gusty SW winds up to 20 kts or so into Mon night. This will maintain seas up between 3 and 5 ft most waters. As the cold front drops south by Tues morning, the winds will diminish to less than 10 kts closer to the coast, but may remain up closer to 15 kts in the outer waters. The front will most likely remain just west of waters through Tues, especially as sea breeze helps to kick it inland a bit. The boundary may be bisecting the area by Tues night into Wed and this could produce lighter and more variable winds heading into Wed morning. Seas should drop to 2 to 4 ft through Tues morning and down to 3 ft or less heading into Wed morning. You can also expect increased thunderstorm activity with front in the vicinity which can produce gusty and variable winds and lower visibility. LONG TERM /WEDNESDAY THROUGH FRIDAY/... As of 300 PM Sunday...A stalled front over South Carolina should provide the trigger for numerous showers and thunderstorms on Wednesday. Winds mainly from the east should remain 10 knots or less outside of storms. Weak low pressure developing along the front should move offshore on Thursday and then well out to sea by Friday. This should allow winds to veer southwesterly. Wind speeds should increase to a solid 15 knots Friday as low pressure develops to our north along a stronger cold front that might reach the Carolinas early next week. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...Small Craft Advisory until 6 PM EDT this evening for AMZ250- 252-254. && $$ SYNOPSIS...RGZ NEAR TERM...DCH/SRP SHORT TERM...RGZ LONG TERM...TRA AVIATION...III MARINE...

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