Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 230139 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 939 PM EDT Sun Apr 22 2018 .SYNOPSIS... High pressure will extend south through the mid Atlantic states through tonight. Low pressure will track slowly eastward over the lower Mississippi Valley and Mid South region before tracking northeast over the East Coast through midweek. && .NEAR TERM /THROUGH TONIGHT/...
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As of 935 PM Sunday... Multiple signs pointing to the inevitable advance of moisture from the west this evening as mid-level cloud decks are expanding across central NC at this time. In addition, observations showing 50s dewpoints now creeping into the southwest Piedmont. Cloud cover will continue to increase overnight as high pressure remains offshore and and a low pressure system works its way across the Deep South. Some lighter returns also starting to show up on radar in the southwest but this is evaporating before reaching the ground. Observed precipitation is still well off to the southwest, closer to Columbia, SC with more significant rainfall still back over Georgia at this time. Lows in the upper 40s across the northeast Coastal Plain where thicker cloud cover will hold off the longest to mid 50s in the southwest Piedmont.
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&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 300 PM Sunday... Overview: Compact closed upper level low over the Lower MS Valley Monday morning will drift slowly NNE across the TN Valley and into the southern/central Appalachians through Tuesday night. Primary surface low associated with this system will remain beneath the mature cyclone and eventually fill with a secondary low at the triple point expected to track NEWD through the Savanna River Valley and into eastern NC Tuesday afternoon/evening, before lifting up along the Delmarva coast Tuesday night and into Wednesday. Rainfall Amounts/Impact: While strong mid/upper level ridging extending along the western Atlantic/Mid-Atlantic coast may initially delay the spread of rain NEWD into the area Monday, rain will become widespread over the entire CWA by late Monday afternoon/early evening. Owing to the slow movement of the upper low across the region, along with a very strong Atlantic maritime feed between the offshore high and the mature cyclone to our west, a widespread soaking of 1 to 2 inches, with localized higher amounts can be expected. The heaviest rainfall is expected to occur Monday night through Tuesday morning, with another round of convective rainfall possible Tuesday afternoon as the surface low and attendant warm sector retreats north into southern/southeastern NC(more on that below). With area rivers and creeks running high from recent heavy rainfall over the past week, this additional rainfall may be enough to result in some localized/minor flooding. Severe Potential: Models are in good agreement that the secondary/triple point low and attendant warm front/sectors(sfc dewpoints surging into the mid 60s) will lift north into southern/southeastern NC Tuesday afternoon. CAD in place across central NC should keep the the warm sector confined to southeastern portions of NC, with mid-level dry air intrusion likely to result in sufficient breaks in cloud cover to allow for partial insolation by the afternoon. Models indicate warm sector destabilization of 500 to 1000 J/Kg of MLCAPE across the eastern Sandhills and southern Coastal Plain counties. Effective shear of 35-40kts will be sufficient to support a few strong to severe storms Tuesday afternoon/early evening with the presence of the dry air aloft (models showing dCAPE values of 750 to 1000 J/Kg) likely to enhance downdraft potential with any strong updrafts that develop. Additionally, with the low tracking NE along the warm/wedge front, cannot rule out an isolated tornado. Stay tune. Temperatures: Rain spreading SW to NE into the area, along with widespread and lowering cloud deck and the development of cold air damming over the NC Piedmont will will keep temps on the cool side Monday. Highs ranging from mid to upper 50s across the NW Piedmont to upper 60s/near across the NE coastal plain counties where rain will be last to set in. Highs Tuesday will be complicated by the ongoing CAD and the exact location/track of the secondary low and attendant warm sector lifting NE into the area. Highs ranging from upper 50s/ near 60 over the northern Piedmont to mid 70s across the southern Piedmont, southern Sandhills and southern Coastal Plain counties. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... As of 245 PM Sunday... Unsettled weather is expected through the middle and end of the work week, with mean mid level troughing dominating over the eastern states, and generally more clouds than sun, at least through Fri. The first shortwave trough (responsible in part for the Mon/Tue rain) will be sitting overhead early Wed before lifting off to the NE, culminating in a phasing with a strong polar stream wave over the Northeast states Wed night. Models suggest that we may see enough low and mid level moisture (focusing on 850-700 mb) for a few late-day showers with heating, however the overall forcing for ascent will be small, and expect no more than chance pops. Expect temps to stay slightly below normal, with thicknesses about 10 m under normal and reduced insolation. The next shortwave, which will be located over NE/KS early Wed, will cross the Gulf states and swing NE over the Carolinas Thu night into Fri. As this feature will be deeper and provide stronger forcing for ascent along with an opportunity for moisture return, we should have higher rain chances, targeting late Thu through Thu night, and some of this may be heavy, as the GFS shows a PW over 1.5". After dry weather late Wed night through the first half of Thu, will bring in good chance pops Thu afternoon through Thu night. Temps should again be a bit below normal figuring in the cloudiness and cooler thicknesses. Then, a deep mid level trough from central Canada through the Upper Midwest early Thu should be our next weather-maker. The GFS/Canadian are in fair agreement on a deep low just to the W or NW of NC late Fri, crossing the Carolinas Fri night or early Sat, although uncertainty and model spread grows at this range. Will keep a chance pop, higher N closer to the cooler mid levels and better lapse rates aloft, Fri/Fri night extending into early Sat. We should see subsidence and drying behind this wave for Sat afternoon through Sun, and will trend toward dry weather and fewer clouds as high pressure builds in from the west. -GIH && .AVIATION /00Z MONDAY THROUGH FRIDAY/... As of 800 PM Sunday... VFR conditions are likely through much of tonight, as surface high pressure noses into NC from the N, but an approaching storm system will bring deteriorating aviation conditions from SW to NE during Mon. High and mid clouds will steadily thicken with lowering bases through tonight from SW to NE, ahead of the slow-moving low pressure system. As cloud bases steadily lower, MVFR cigs are expected after 09z tonight in the SW part of the forecast area toward CLT. Cigs are likely to drop to MVFR at INT/GSO after 12z Mon, with vsbys falling to MVFR after 15z as rain spreads in from the SW and becomes more steady. MVFR conditions are then expected to move to RDU/FAY after 16z, with conditions at INT/GSO trending to IFR. Surface winds will increase from the SE and become gusty late tonight and through Mon, particularly over S and W sections (including INT/GSO/FAY), with stronger and shifting winds with height, potentially resulting in handling difficulties with smaller aircraft starting early Mon. Looking beyond 00z Tue: Poor aviation conditions will dominate all sites through Tue as a strong and slow-moving storm system crosses the area. Periods of showers and sub-VFR conditions are likely. On Tue, FAY and perhaps RDU/RWI may see some breaks in the sub-VFR conditions with a risk of storms. Rain should taper off Tue night but sub-VFR stratus/fog may linger into Wed morning. VFR conditions should return Wed, although a few showers are possible Wed afternoon, and again Thu into Fri, as a series of upper level troughs cross the region, bringing unsettled weather and perhaps brief periods of sub-VFR conditions. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NC...None. && $$ SYNOPSIS...Hartfield NEAR TERM...Ellis SHORT TERM...CBL LONG TERM...Hartfield AVIATION...Hartfield

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