Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 240611 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 211 AM EDT SUN JUL 24 2016 .SYNOPSIS... A ridge of high pressure will expand across the Carolinas bringing increasingly hot and humid conditions through the weekend and much of next week. Isolated showers and thunderstorms are possible each afternoon, and heat advisories will likely be needed each day beginning Sunday. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... As of 1 AM Sunday...No changes to the forecast with the latest update. Previous discussion follows: A hot subtropical ridge is centered near Memphis, TN and extends back into Texas while the Bermuda ridge is well offshore. As upper level heights continue to rise across West Virginia our steering flow is turning more northeasterly since we are south of the ridge axis. This was apparent with this evening`s thunderstorms which tended to move slowly toward the southwest when they weren`t following boundary collisions. These storms formed within a moderately unstable environment with weak shear but rich low-level moisture. The strongest cell of the night near Fairmont in Robeson County, NC displayed some interesting radar velocity signatures prompting a Special Weather Statement for possible 50 mph winds. Radar rainfall estimated were up to 3.7 inches in southern Robeson County. No reports were received from the public. Unlike last night there are no identifiable upper impulses to help sustain or redevelop convection overnight. In fact temperatures should warm at the 700 and 500 mb levels by about a degree C overnight which will help stabilize things further. With the evening convection now pretty much done, the only reason I can find to maintain any mention of rain in the overnight forecast is as the landbreeze pushes off the coast it may be able to develop a few showers or t-storms offshore. Steering flow will tend to push any developing cells back toward the southwest which means the coast of South Carolina could see some activity very late tonight. I`m holding pops at only 20 percent for now, redeveloping between 4-6 AM. Very few changes have been made to the rest of the forecast. Lows should fall into the mid 70s for most locations, perhaps a little cooler where rain fell earlier and winds have gone calm. && .SHORT TERM /6 AM THIS MORNING THROUGH MONDAY NIGHT/... AS OF 330 PM SATURDAY...Hot and dry will be the rule beginning Sunday as a massive ridge of high pressure envelops much of the southern tier of the CONUS. Although the ridge itself does not have tremendous latitudinal amplitude, it is quite strong and 1000-500mb thicknesses rise towards 580dm Sunday and Monday, with heights climbing towards 595dm directly overhead the Carolinas by Monday aftn. At the same time, 1000-850mb thicknesses approach 1435m, fueling 850mb temps around 20C. This ridge suppresses a weak mid-level low to the SW, moving overhead Florida late Sunday, with easterly flow developing through all but the lowest 100-150mb of the column. Typically this is a moistening flow direction, but in this case trajectories originate from a dry air mass offshore, and PWATs drop towards the bottom quartile for late July by Monday. At the surface, return flow prevails however, so ample sunshine combined with warm/moist flow and bulging thicknesses aloft will create hot and humid conditions but with very few tstms. Highs Sunday will rise well into the 90s, with mid 90s expected inland and around 90 at the beaches. On Monday, temps will be just a bit cooler thanks to the aforementioned upper low causing slightly reduced thicknesses, but will still rise into the low 90s. These hot temps combined with dewpoints climbing back into the low/mid 70s, will necessitate a heat advisory for Sunday, and one has been issued, valid from 11am to 8pm, for all zones. Slightly cooler temps and and lower dewpoints Monday will keep heat index values just below advisory thresholds. Mins both nights will be well above climo, mid and upr 70s. While the airmass will be very unstable this period, convection will be isolated at best, thanks to increasingly dry air aloft and warming mid-level temps. Although 500mb and 850mb temps drop a bit on Monday, the airmass dries even further, so will cap POP at SCHC Sunday and Monday, with the highest values along the sea breeze in SC. && .LONG TERM /TUESDAY THROUGH SATURDAY/... AS OF 330 PM SATURDAY...Overall medium range guidance is pointing to strong mid level ridging, on the order of 594DM Tuesday into Wednesday. Heights slowly fall from that point onward through the remainder of the period. Other than the Piedmont trough, still not much in the way of forcing for convection. Certainly subtle mid level features will help to kick off activity but all but impossible to pinpoint at this time. The forecst of slowly increasing pops still looks good with the best chance Thursday when PWs jump to just over two inches. No changes to the temperature forecast. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/...
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As of 06Z...Ridge of high pressure extends over the Carolinas with a light southerly return flow at the surface providing a warm and moist air mass. A few shwrs may develop just off the coast early morning as land breeze develops and these may get pushed on shore in the morning. Overall expect winds to back to the south in the aftn sea breeze and veer to the SW in land breeze overnight. Showers should develop along sea breeze front toward early aftn as it pushes inland and much farther inland along the piedmont trough, but with ridge overhead do not expect support for more than isolated convection. Have included only VCTS for coastal terminals with steering flow pushing most showers off to the north. EXTENDED OUTLOOK...Isolated to scattered afternoon convection Tuesday through Thursday may create periods of MVFR/IFR. Otherwise expect VFR.
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&& .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 1 AM Sunday...No changes to the forecast with the latest update. Previous discussion follows: Bermuda High Pressure well offshore is maintaining southwesterly winds across the Carolinas at 10-15 knots. This is the climatologically typical pattern for mid summer. Winds should veer a little more westerly overnight as a weak landbreeze forms. The latest several HRRR model runs suggest the landbreeze front could ignite a few showers or t-storms late tonight, especially south of Cape Fear. Steering winds would tend to push whatever showers might develop toward the southwest. Seas are only 2 feet with dominant 8-9 second periods. SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 330 PM SATURDAY...Bermuda ridging will remain the most influential feature through the short term, creating consistent wind and wave conditions. SW winds will prevail both days, with speeds increasing from around 10 kts Sunday, to 10-15 kts on Monday. A persistent but weak 2ft/8sec SE swell will exist in the spectrum, but avg wave periods will gradually shorten as a SW 4-5 sec wave amplifies. Wave heights will be 2-3 ft through Monday, becoming more uniformly 3 ft late. LONG TERM /TUESDAY THROUGH THURSDAY/... AS OF 330 PM SATURDAY...Expect south to southwest winds of 10-15 knots through the period as the Bermuda Azores high pressure system and the Piedmont trough are the main drivers of winds. Significant seas will be 1-3 feet with wave periods mostly confined to shorter period wind waves. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for SCZ017-023-024-032-033-039-053>056. NC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for NCZ087-096-099-105>110. MARINE...None. && $$ SYNOPSIS...SHK NEAR TERM...REK/TRA SHORT TERM...JDW LONG TERM...SHK AVIATION...DL MARINE...REK/TRA/SHK

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