Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 200747 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 321 AM EDT Thu Jul 20 2017 .SYNOPSIS... Showers and thunderstorms will be isolated in the days ahead, as an upper ridge builds from the west. The ridge will bring hot and humid conditions through the weekend. Rain chances will increase early next week, as a surface trough deepens inland. && .NEAR TERM /THROUGH TONIGHT/... As of 321 AM Thursday...Upper level low clearly evident on WV imagery this morning spinning off the SC coast will continue to drift slowly southward while 500mb ridge begins to expand from the MS VLY. At the surface, broad high pressure will remain but with a very diffuse gradient in place. This leaves the upper low as the primary influence on today`s weather. An upper low overhead in July typically means steep lapse rates and convection. While the former is true, with stronger than moist- adiabatic lapse rates seen on forecast profiles between 700 and 500mb, the latter will be tough to come by today. Anomalously strong easterly flow aloft (-2 to -3 sigma) will advect drier air into the column with PWATs falling to around 1.6 inches this aftn. Additionally, coupled 250mb jet structure atop the 500mb upper low will actually drive confluence overhead, likely forcing some sinking motion noted by weak negative omega. Despite these features working against convection today, MLCape climbing over 1500 J/kg could still support an isolated tstm, most likely along the sea breeze, and have carried SCHC POP for the sea breeze boundary only. Do not expect activity on the Piedmont Trough today. This cape is driven by what will become the hottest day so far this week (although this will most certainly be eclipsed Fri and Sat) combined with still high dewpoints. Some drier mixing is forecast this aftn so heat index values are expected to remain in the upper 90s to around 100 as temps climb into the upper 80s NE zones, to as warm as 95 in the far SW Pee Dee counties. Developing southerly flow this evening and tonight will keep mins elevated despite mostly clear sky conditions, and forecast lows are only around 75 most locations. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
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As of 321 AM Thursday...Primary feature of note this period is broad upper ridging exerting eastward into the area, as a hot dome of air aloft expands into the Carolinas. This may squelch rainfall across the area altogether and have kept mentionable POP values below the 15% threshold both Friday and Saturday. Enough h8-h7 moisture remains trapped below the warm air and moderate diurnal cumulus is a certainty each afternoon. The heat indices will be on the uptick and a heat advisory may be needed for portions of NE SC and SE NC on Saturday. Apparent temps will range from 98-103 Friday and 100-106 on Saturday.
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&& .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 3 PM Wednesday...The first half of the extended period, basically the weekend will feature mostly dry conditions with temperatures somewhat above normal. These conditions will be provided by a weak mid level pattern and Bermuda High Pressure at the surface. The mid level capping is not quite as prominent on soundings as it has been in recent days, but with mid level moisture lacking convection will still drive a hard bargain. The second half of the extended, early next week shows more favorable conditions for convection as cooling aloft and an increase in column moisture to well over two inches warrants. Temperatures fall slightly from the weekend`s warmer readings. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... of 06Z...Diffuse pressure gradient in place across the area has left nearly calm winds at the terminals. The exception to this is near the coast where a land breeze has developed and winds will be from the west at 5 kts or less into Thursday morning. With a very moist ground persisting and these light winds with clear sky conditions, fog is possible tonight. However, local UPS fog procedures are not robust with fog development, and mins remaining above 70 may be too warm for any significant vsby reduction. Have included tempo MVFR at FLO/LBT, but attm do not expect any IFR tonight. Forecast profiles do suggest some IFR stratus inland, but confidence is low in that as well as this setup would seem to favor fog over stratus. At the coast, no restrictions are anticipated. A hot and dry day forecast after sunrise with sct diurnal VFR CU and maybe an isolated tstm. The best chance for this will be near the Myrtles this aftn, but coverage is expected to be too limited for a TAF mention. Winds will remain light, but become S/SW at 5-10 kts all terminals, highest at the coast within the sea breeze. Most CU will erode with loss of heating at the end of the valid period leaving mostly clear sky conditions once again and VFR. Extended Outlook...VFR. Scattered showers and thunderstorms Monday. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 321 AM Thursday...A land breeze through early morning will gradually give way to more typical return synoptic flow this aftn through tonight. The pressure gradient today is very weak, so whether the winds are coming from the west this morning, or the S/SW this aftn and later, speeds will be 10 kts or less. The exception to this will be brief increases within the sea breeze circulation. These light winds allow the 2-3ft/7sec SE swell to be the primary driver to significant seas today, creating 2-3 ft seas will little fluctuation. SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 321 AM Thursday...The intensifying heat inland will bring a robust sea breeze each afternoon Friday and Saturday, and gusts to 20 KT like certain at this time. Otherwise expect sustained winds from the SW 10-15 KT through the period. Seas of around 3 feet should be expected, in a mix of Sw waves between 1-2 feet every 3-4 seconds, and SE waves 2 feet every 9 seconds. The dry air aloft will keep TSTMS away from the area this period but a few showers near the Gulf Stream may pop up. LONG TERM /SUNDAY THROUGH MONDAY/... As of 300 PM Wednesday...Bermuda High Pressure will maintain a summertime flow across the waters. Mariners can expect a southwest flow of 10- 15 knots with some late morning/afternoon acceleration with the sea breeze near shore. Significant seas, without the assist from any meaningful swell component will fall into a range of 2-4 and mostly 2-3 feet. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...Colby NEAR TERM...JDW SHORT TERM...8 LONG TERM...SHK AVIATION...JDW

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