Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS62 KRAH 210023 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 821 PM EDT Sat May 20 2017 .SYNOPSIS... A backdoor cold front will settle southwest through central NC tonight, stalling over the Southern Piedmont and Sandhills Sunday. Cooler high pressure will build into NC from New England tonight and Sunday. Low pressure and a cold front will approach from the west Sunday night, then move slowly east into central NC Monday. && .NEAR TERM /THROUGH TONIGHT/... As of 821 PM Saturday... An isolated severe thunderstorm is possible through 1200 AM for north-central NC... A cold front was surging to the southwest across central NC this evening. The front at 800 PM extended from Roxboro to Raleigh to Clinton, moving in backdoor fashion toward the Sandhills and western Piedmont. Winds increase from the NE with the frontal passage and the temperatures drop about 5-7 degrees in an hour. The 800 PM readings ranged from 68 at Roanoke Rapids to 77 at Louisburg, to 83 at RDU and GSO. Only an isolated shower or two have been observed associated with the front, with deep convection confined to VA and along the Coast, which has since moved offshore or dissipated. Scattered convection over southern VA, with at least one severe storm, just NE of Danville VA appear to the the area to watch over the next few hours. The latest data suggests that moisture convergence/pooling along with the highest CAPE should be focused along the westward moving cold front. This would place areas from Roxboro and Raleigh west to the Triad in play for higher POP for scattered convection. Elsewhere, cooler and more stable air should continue to advect into the Coastal Plain from off the Atlantic essentially shutting down convection threat for the Coastal Plain (with the exception Sampson County where the cold front was still to push through). We will carry 20-50 POP (highest in the north-central Piedmont, with 10 POP in the far NE from Goldsboro up the Interstate 95 corridor. Post-frontal low overcast will lag the front later tonight, but will spread in from the NE overnight in all but the SW zones. Lows generally 60-68 NE to SW. && .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... As of 345 PM Saturday... The cold front is forecast to have settled to a position just to the SW of the RAH CWA, or perhaps over the far srn Piedmont, by 12Z Sunday, with a following surface ridge axis extending SWwd from a parent 1030 mb high along the nrn Middle Atlantic coast. Associated CAD and widespread low overcast trapped beneath a strong inversion should consequently be firmly entrenched across central NC through early Sunday, with a gradual Nwd retreat of the front, and associated lifting and scattering of the low overcast through the afternoon. There is a relative high degree of confidence that the warm sector will consequently expand across srn NC Sun afternoon, where temperatures will likely warm well into the (mid-upper) 80s; and there is a similarly high degree of confidence that the low overcast and continued cool conditions in the 60s to near 70 degrees will linger over the far nrn Piedmont. In between, however, in or just south of the larger metropolitan areas, there is large temperature bust potential of 15-20 degrees. Precipitation, in the form of light rain/showers, will be favored along and north of the front early Sun, then become favored along it over srn NC, and with an increasingly deep convective character, by Sun afternoon. A series of disturbances in SW flow aloft, including some convectively-generated or enhanced ones from upstream convection over the lower MS Valley, will track across the Carolinas later Sun and Sun night; and these will promote the development and slow Ewd progression of a band or bands of showers and storms into the western half of the RAH CWA overnight, with a half to one inch of rain probable there by 12Z Mon, and with much lower to nil amounts east of U.S. Hwy 1. Otherwise, areas of low overcast will redevelop, or lower where they remain throughout the day Sunday, by late evening. Near steady overnight temperatures in the middle to upper 60s are expected. && .LONG TERM /MONDAY THROUGH SATURDAY/... As of 245 PM EDT Saturday... A long wave trof amplifying over the central CONUS will provide us with active weather featuring a couple of frontal passages with below-normal temperatures and potentially 2+ inches of rain across central NC through mid week. An initial front will be moving across the mountains on Monday, with prefrontal convection increasing across the western piedmont during the morning and shifting to the east by mid afternoon. Thunder will accompany the system, but severe potential is low with only modest shear (30Kts of low level flow) and instability (mid level lapse rates <6K/km in warm southwest flow limiting CAPE to ~500J/kg... mainly in the east). Will have 80% PoPs transitioning across the area with the front and rainfall ranging from 0.5 to 1.0 inches through Monday night, although localized heavier showers accompanying storms could double that amount. Highs will range from the mid 70s west to some very low 80s in the east where frontal passage will be later. Even as the front moves offshore, a mid level wave will lift out of the Gulf in deep southwest flow and ride northeast into the area quickly on Tuesday. Will lean towards higher chance PoPs through Tuesday night considering that both ECMWF and GFS are converging on some variation of this scenario. Post-fropa and with continued heavy cloudiness, expect highs mainly in the mid 70s. A cutoff low digs south into the Tennessee Valley, pushing another front towards the area approaching on Wednesday. Drying and cooling in the mid levels will produce a thermal profile more conducive to strong storms Wednesday into Wednesday night, will bear watching and will bump PoPs up a bit through the period. We`ll see proper dry slotting ahead of the cutoff low Thursday, with potential for wrap around showers/isolated thunder...mainly across the the low lifts into the mid Atlantic Thursday night. Then, finally, a dry forecast for Friday and Saturday as high pressure builds in from the west. Highs Wednesday through Friday will be mainly in the mid to upper 70s...with some airmass moderation on Saturday edging us back towards normal...low to mid 80s. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... As of 155 PM Saturday... Scattered showers and storms are expected to soon develop along a pre-frontal surface trough axis now draped along an ROA-TDF-RWI-OCW arc; and this convection and associated outflow boundary should then settle southwestward toward RDU by 22Z. Probability of shower/storm occurrence is less at INT/GSO/FAY, since the convection is likely to weaken with time owing mostly to nocturnal cooling. A surface cold front lags the aforementioned pre-frontal trough by about 60 miles; and this boundary and associated leading edge of more marked ENE surface winds will settle southwestward through central NC through around midnight. Of greater operationally significant concern, post-frontal IFR-MVFR ceilings will develop within a few hours of the frontal passage - first around 02-03Z at RWI and last around 07-08Z at FAY. Those ceilings will generally persist through the end of the 18Z TAf period. However, the front will retreat gradually northward as a warm front and result in ceilings lifting to above 2000 thousand feet and/or a scattering to VFR in the FAY vicinity by around 18Z. A similar trend toward high end MVFR ceilings and/or (at least short-lived) scattering to VFR will be possible as the front continues a slow retreat toward the Piedmont TAF sites throughout the afternoon Sunday, but with a redevelopment of IFR ceilings and MVFR-IFR visibility restrictions area-wide shortly after the onset of nocturnal cooling Sunday night. Outlook: Unsettled weather, including periods of rain/convection, and sub-VFR conditions are expected as an upper level trough and preceding moist SWly flow aloft approach from the west, combined with waves of surface low pressure that are forecast to track across the Carolinas early to mid next week. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Badgett NEAR TERM...Badgett SHORT TERM...MWS LONG TERM..MLM AVIATION...MWS is the U.S. government's official web portal to all federal, state and local government web resources and services.