Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 230813 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 412 AM EDT Mon Apr 23 2018 .SYNOPSIS... Strong high pressure will remain nearly stationary or slowly drift off the New England coast through tonight. Low pressure approach from the Tennessee Valley today and tonight, then track slowly east over SC on Tuesday, then NE across eastern NC late Tuesday and Tuesday night. && .NEAR TERM /THROUGH TONIGHT/... As of 315 AM Monday... Increasing easterly winds and timing/amount of rain are the main issues today and tonight... Current projections suggest that East winds will increase to 20 to 30 mph late this afternoon and tonight, with gusts to 35 mph. QPF on the order of 1 to 1.5 inches expected through 12z/Tuesday. Severe thunderstorms not expected through 12z/Tuesday. The mid/upper low near Memphis is forecast to slowly drift NE toward southern KY by 12z/Tuesday. The associated surface low is expected to slowly weaken and move east through the Tennessee Valley and weaken with time, with secondary development over SC by 12z/Tue. An impressive 40-45kt SE low level jet will bring the plume of deep subtropical moisture from the Caribbean and SW Atlantic NW into our region. Rain is expected to continue to expand northward with time today, reaching the southern and western Piedmont between 12z and 15z, then the western Sandhills and rest of the Piedmont between 15z and 21z. The rain will be light to start, then gradually pick up in intensity through the day from SW to NE. The steady rain should reach into the far NE counties before sunset today. Rain, some heavy is expected for all areas tonight. As far as the impacts, the wind will be an issue beginning by early afternoon as the easterly winds increase to 15-20 mph. The winds will increase through the afternoon and evening as the H85 SE low level jet increases to 40-45kt. This jet will help drive and increase surface winds to 20-25 mph with gusts to 30-35 mph as mixing occurs with the steady rainfall. The main timing of these stronger winds appears to be 21z/today through much of the night. With the newly leafed out trees, the heavy rain and wind gusts may down some limbs and we will mention this in the Hazardous Weather Outlook. The other impact from this system will be the rain, potentially heavy at times. There continues to be signal within many of the ensemble solutions that there may be a minimum of QPF over a portion of inland NC (possibly the southern Piedmont of NC / Sandhills). This is due to the favored maximums of QPF to be in the upslope areas of western NC and along the coast. The maximum (if if it develops along or near the coast) may be convectively driven from a secondary low pressure circulation along the coastal front. If this develops, it may focus the convection and heaviest rain there and there may be a shadow or minimum of QPF to the NW of this area. Even if this shadow or minimum occurs, there should still be "healthy" totals in the 1 inch range, with 1.5 to 2.5 inches in the upslope or higher Piedmont areas to the NW, but focused even more so along the east slopes of the Blue Ridge. Locally 3+ inches may occur there. The higher QPF (locally 1.5 to 3 inches in 12-24 hours) would still fall short of the Flash Flood Guidance criteria. Therefore, with the uncertainty in the heavier QPF to fall over all the region and with the FFG being rather high after the drying out period this past week, we will simply mention the chance of some minor flooding in urban and poor drainage areas in the Hazardous Weather Outlook. Severe thunderstorms are not expected through at least 12z/Tuesday as the entire area will have widespread stratiform rain that will keep the instability at near zero. The warm/coastal front will still be south and southeast of our region by 12z/Tuesday, with the only chance of convection expected to be elevated on the cool side of the boundary. Sensible weather includes: Rain developing/overspreading central NC (west this morning, east this afternoon). Highs upper 50s west, to near 70 east. Winds increase to 20-30 mph late today and tonight with rain. Lows in the 50s to near 60 (SE). && .SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
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As of 350 AM Monday... An elongated srn stream mid-upr low over the mid-South this morning is forecast to wobble to near BNA by 12Z Tue and to swrn VA by 12Z Wed. Preceding the upr low, the right entrance region of a strengthening sly to ssely, 80-100 kt upr level jet will stream across e-cntl NC and sern VA through 18Z Tue. Associated divergence aloft, atop a strong low level WAA/isentropic upglide regime courtesy of a 40-45 kt low lvl jet, will support ongoing widespread rain and embedded elevated convection (showers), early Tue. This regime will lift newd into and offshore VA through early afternoon, followed by a mid level dry slot that will nose across the Carolinas Tue afternoon and evening. At the surface, the models indicate a triple point low over nern GA/wrn SC at 12Z Tue will track newd into the srn NC Piedmont/wrn Sandhills by 00Z Wed, then track nnewd roughly along US Highway 1 Tue night. A preceding warm front will arc enewd across srn and sern NC early Tue, with the trailing cold front extending swd along the srn SC and GA coast. The cold front is forecast to progress ewd more quickly than the warm front retreats nwd, with an associated increasingly narrow wedge of warm sector characterized by low-mid 60s surface dewpoints and mainly weak sfc-based instability, which is forecast to pivot newd across nern SC and ern and e-cntl NC Tue afternoon, beneath the aforementioned mid lvl dry slot. Low lvl and deep layer flow will have weakened considerably and veered in the wake of the early day WAA/isentropically-driven rain, though lingering effective SRH on the order of 100-150 m2/s2 immediately preceding the surface wave may support episodic low level rotation in showers/storms late Tue aft-evening. However, a lack of more appreciable instability and shear suggests any severe weather threat over cntl NC should be limited. Showers will linger Tue night, particularly over the Piedmont, as the mid-upr low and associated cold pool aloft pivot overhead. Temperatures Tue are expected to range from low-mid 60s in a lingering damming regime over the NW Piedmont (nw of the track of the surface low), to low-mid 70s across the Sandhills and srn-cntl Coastal Plain, with lows in the 50s.
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As of 400 AM Monday... An energetic, unsettled pattern will persist through most of the medium range, though uncertainty regarding amplitude and phasing of associated shortwave troughs migrating through the energetic flow lend low forecast confidence for prospects for rainfall in cntl NC. A trough now over the PAC NW will have amplified into the cntl Plains by 12Z Wed, and into the TN Valley/srn Appalachians by 00Z Fri, before then deamplifying across the Carolinas/srn middle Atlantic states through early Fri. A full latitude trough will follow quickly on the heels of the lead trough and pivot ewd across the Appalachians and NC Fri night-Sat. Following NW flow downstream of progressive ridging aloft will overspread the srn middle Atlantic region for end of weekend and early next week. This pattern will favor variably to mostly cloudy conditions and above climo chances of rain by late Thu-Fri, followed by lingering slight chances Fri night-Sat given the aforementioned uncertainty regarding shortwave details, and dry conditions as the NW flow takes hold by Sun.High temperatures will be seasonable/slightly below average - mostly in the lwr-mid 70s, with near to slightly above average low temperatures, in the upr 40s to lwr-mid 50s.
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&& .AVIATION /06Z MONDAY THROUGH FRIDAY/... As of 1245 AM Monday... MVFR to VFR CIGS will lower to IFR TO LIFR CIGS and IFR VSBYS with rain and fog later today and tonight. Winds will increase from the east at 15-20kt with gusts to 30kt this afternoon and tonight. Looking beyond 06z Tue: Poor aviation conditions will dominate all sites through Tuesday. Mostly IFR CIGS and IFR to MVFR VSBYS with areas of rain and showers are likely on Tuesday, before tapering off Tuesday night. 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. && .RAH WATCHES/WARNINGS/ADVISORIES... NC...None. && $$ SYNOPSIS...Badgett/Hartfield NEAR TERM...Badgett SHORT TERM...MWS LONG TERM...MWS AVIATION...Badgett/Hartfield is the U.S. government's official web portal to all federal, state and local government web resources and services.