Area Forecast Discussion
Issued by NWS Wilmington, NC

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092 FXUS62 KILM 191250 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 850 AM EDT Wed Jul 19 2017 .SYNOPSIS... Showers and thunderstorms will become more isolated in the days ahead, as an upper ridge builds from the west. The ridge will bring hot and humid conditions late this week through the weekend. Rain chances may increase early next week, as a surface trough deepens inland. && .NEAR TERM /THROUGH TONIGHT/... As of 900 AM Wednesday...Updated forecast to cover a cluster of thunderstorms moving north across New Hanover County and eastern Brunswick County. Otherwise the radar scope looks clear of convection. HRRR not very bullish on convection for the remainder of the day, with isolated sea-breeze showers the main attraction. Previous discussion follows: Interesting and atypical synoptic pattern evolving across the Southeast as large upper low cuts off overhead and begins to drift southward. This low gets shunted southward thanks to ridging both to the east and west, and a shortwave moving to the north unable to capture the local feature. The presence of this low overhead will keep lapse rates relatively steep, which during peak heating allows MLCape to climb to 1500-2000 J/kg. However, as the low spins slowly to the south PVA becomes weak and winds above the surface shift to the W/NW - a drying direction. This is noted by PWATs falling to 1.5 inches and decreasing saturation in forecast profiles. For this reason, expect minimal convective coverage today despite what should be abundant diurnal CU. Have maintained SCHC POP for all locations, with development most probable along the sea breeze and the piedmont trough this aftn/eve. Convection will wane with loss of heating, and a quiet night is expected. As far as temperatures go today, the forecast is a bit tricky. Downslope flow the first part of the day should allow the region to heat up quickly before CU becomes significant. The surface winds will shift slowly to the south this aftn, and a sea breeze is expected, but may get a late start as it is pinned initially. This downslope flow is usually a heating wind, and most places will reach 90 away from the beaches this aftn. However, have tried to show temps below guidance across the Pee Dee where recent heavy rainfall (200-300% of normal in the last 7 days) has created very moist soils which should keep temps a bit cooler than forecast models suggest. The opposite is true near the coast where the downslope flow and a late sea breeze will help temps climb just above guidance. Mins tonight will drop only into the mid 70s most places as increasing southerly flow keeps temperatures from falling much. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 345 AM Wednesday...This time range features relatively dry air above 10,000 feet, as an upper ridge nudges into the region from the west, and a weak cool pool dips south of the forecast area. There may be enough h8-h7 moisture Thursday to trip off convection near the pinned sea breeze in low-level west wind flow, but Friday the H8-H7 layer will dry out a bit, and have kept measurable rain odds below the mentionable threshold of 15 percent. Heat indices of 98-102 degrees Thursday, will increase to 100-104 Friday, and a Heat Advisory is not entirely out of the question Friday if either air temp or dewpoint is raised only slightly. Only general TSTMS depicted Thursday and no severe weather signals or flooding parameters appear to be in place this time period. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 300 PM Tuesday...Initially mid level low pressure will be wobbling westward along the Gulf Coast undercutting a potent ridge centered along the Mississippi Valley. This area or Col in meteorological parlance will keep convection to a minimum via mid level capping although this time of year it can never be ruled out. I suspect as we move forward in time small pertubations may show up in the weak circulation thus increasing pops albeit slightly. The pattern becomes more conducive for convection in time and this is reflected in the later parts of the forecast. Guidance has trended a little lower on overall temperatures especially the ECMWF but still expect most of the period to see temperatures somewhat above normal. && .AVIATION /13Z WEDNESDAY THROUGH SUNDAY/... As of 10Z...Upper low Will continue to spin overhead through the valid period. IFR is expected inland where heavy rainfall fell earlier. A moist ground combined with weak WAA is usually a good setup for IFR, and guidance in good agreement developing stratus at LBT/FLO TIL 13Z. At the coast, rain did not occur this evening, and WV imagery shows much drier air aloft. This may allow for some MVFR fog at the coast with 20 kts of wind at 2kft preventing more significant vsby reduction. Any restrictions will erode by 13z with VFR developing. Much drier air aloft will preclude much more than isolated convection this aftn/eve, despite the upper trough persisting. It is possible a terminal will receive a shower or tstm today, but this will need to be handled with short duration AMDs, and coverage is expected to be isolated enough that even VCTS has not been added. Winds will be light through the period, from the W early and backing to the S this evening, with speeds 10 kts or less, highest at the coast. More fog/stratus is possible Thursday morning. Extended Outlook...Fog and stratus possible Thursday morning persisting just after 12z. VFR thereafter. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 900 AM Wednesday...Updated forecast to cover thunderstorms moving north across AMZ250 this morning. Otherwise, all is quiet, with seas only around 2 ft and light winds. Previous discussion follows: Westerly flow through the morning hours will quickly transition to S/SW as high pressure expands from the Atlantic. The gradient will remain weak today, so regardless of direction wind speeds will be less than 10 kts, the exception being some locally higher winds within the sea breeze circulation this aftn/eve. These light winds allow the persistent SE swell to be dominant within the spectrum, creating seas around 2 ft with a 7-8 sec average period. SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 345 AM Wednesday...No problems on the waters this period as seas remain manageable, and less TSTM coverage expected than the recent days. S-SW winds both days 15 KT or less, but gusts to 20 KT possible inshore during the middle and late afternoons due to a robust sea breeze. Seas around 3 feet this period in a mix of SE waves 2-3 feet every 7-9 seconds and SW waves 1 foot every 4 seconds. LONG TERM /SATURDAY THROUGH SUNDAY/... As of 300 PM Tuesday...Expect southwest winds of 10-15 knots for the duration. There will inevitably be some nocturnal acceleration from time to time but this amount of detail is all but impossible to put into the extended. Significant seas will be 2-4 feet. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...MJC NEAR TERM...REK/JDW SHORT TERM...MJC LONG TERM...SHK AVIATION...MJC MARINE...MJC/REK/JDW/SHK

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