Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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567 FXUS62 KRAH 231049 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 650 AM EDT FRI SEP 23 2016 .SYNOPSIS... A surface low and trough will hold along the Carolina coast through today, before weakening tonight. Weak high pressure will hold over the area through Saturday, then a backdoor front will push in from the north Saturday night and Sunday. && .NEAR TERM /THROUGH TONIGHT/... As of 645 AM Friday... Minor update to account for low coverage of light precip confined to the southeast CWA this morning. -GIH Earlier discussion from 240 AM Friday: Rain chances will finally be dwindling, but not before another round of scattered showers and few storms through this afternoon, mainly southeast of the Triangle. Surface low pressure persists just off the SC coast with a weakening inverted trough extending across coastal NC, capped by a persistent mid level shear axis over central/eastern NC. PW and low level moisture convergence remain rather high today over the eastern and southern portions of the forecast area, warranting a continuation of good chance pops there, in line with consensus of guidance from parameterized-convection models, convection-allowing models, and ensemble output. Chances will be low (0-20%) in the NW CWA as drier air (noted just to our NW on water vapor imagery) and warmer/more stable mid levels ease toward the ESE as the mid level shear axis likewise drifts to the ESE today. Will include a mention of just isolated thunder in the SE CWA, with model forecasts of marginal instability and poor deep layer shear. Low level thicknesses adjusted for greater sunshine in the NW CWA and greater cloudiness with later partial clearing in the SE supports highs in the lower- mid 80s, cooler in south-central sections and warmer in the NW. PW values fall from NW to SE late today into the evening, with lowering low-level moisture transport and rising heights aloft from the west as central-CONUS ridging starts to build in. Will trend pops down and out for tonight, with a trend to mostly clear (NW) / partly cloudy (SE). Lows in the mid-upper 60s. -GIH && .SHORT TERM /Saturday through Saturday night/... As of 255 AM Friday... Dry and very warm weather expected. Mid level ridging aloft continues to build in from the west, while at the surface, the weak trough drifts further offshore as weak high pressure moves in from the west, although lee troughing does form in the afternoon over the western Piedmont. With low PW and a fairly stable column, will keep pops under 15%, with mostly sunny skies. Thicknesses and statistical guidance indicate highs in the mid-upper 80s, around 6-10 degrees above normal. The anticipated backdoor front moving toward NC from the NNE is poised to move into the NE CWA Sat night into early Sun morning, driven by energy rotating around a large vortex centered near the Newfoundland/Quebec border. But this low does not appear to dig markedly down the East Coast, hinting that the front may not work very far into NC despite being propelled by a cool dense surface high to our north. The ECMWF tends to hold the front just north of the VA/NC border through daybreak Sunday, while the NAM/GFS dip the front into northern NC. Will lean toward the ECMWF solution and hold onto mild temps overnight, with lows Sat night in the mid- upper 60s and a minimal drop in dewpoints over the NE. Regardless of frontal progression, we are likely to see increasing clouds from NNE to SSW Sat night. While a few models generate shower activity ahead of or along the front over north central and NE NC Sat night, the presence of features to force ascent is uncertain, and will opt for dry weather for now and monitor trends. -GIH && .LONG TERM /Sunday through Thursday/... As of 320 AM Friday... Confidence in the long term forecast is still fairly low but nothing like it was yesterday morning as model solutions are slowly starting to come up with somewhat of a common solution. The big difference maker, which was the blocking pattern in the GFS solution is not showing up as much as in previous runs and has allowed high pressure over to come southward out of Quebec on Sunday to become more transitory and move into New England on Monday and out to sea on Tuesday. This allows a cold front to drop into the Carolinas on Wednesday, hang up over the area on Thursday before exiting to the south Thursday night into Friday. During this time period the best chances for thunderstorms would be on Tuesday and Wednesday ahead of and with the cold front. Otherwise some slight chances for rain throughout the period, mostly in the form of diurnal showers are possible. Temperatures will generally stay in the upper 70s to low 80s before the cold front with some hints at some highs in the mid 70s for the end of the week. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... As of 650 AM Friday... Widespread IFR to LIFR conditions will linger through 12-13z this morning across all of central NC, a result of light winds along with stable and very moist air in the low levels. Cigs are expected to rise to MVFR between 14z and 16z, and then to VFR between 16z and 18z west (INT/GSO), 18z-20z central (RDU), and 19z-21z east (RWI/FAY). Rain chances today are low west (INT/GSO) trending higher east (RDU and especially RWI/FAY), with the highest coverage near FAY, which could see a few hours of showers, and perhaps a storm or two, with MVFR vsbys and cigs this afternoon. Conditions will trend toward VFR everywhere after sunset tonight, as weak high pressure starts to build in from the west with drier air moving in. Looking beyond 12z Sat morning, VFR conditions will dominate into Sat evening, with the risk of sub-VFR stratus and fog returning late Sat night/Sun morning as a backdoor front approaches from the north. MVFR cigs may linger through much of Sunday and Sunday night, although confidence is not high, as there is uncertainty regarding the southward pace of the backdoor front through NC. After mostly dry weather Sat, the chance for sub-VFR showers and storms returns for Sunday along the backdoor front. Shower/storm chances will increase further late Mon into Tue as an upper level low pressure trough approaches from the NW. There may be a risk for low level wind shear early Tue morning. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield SHORT TERM...Hartfield LONG TERM...Ellis AVIATION...Hartfield is the U.S. government's official web portal to all federal, state and local government web resources and services.