Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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126 FXUS62 KRAH 301952 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 252 PM EST Wed Nov 30 2016 .SYNOPSIS... A cold front will approach the area this afternoon and then move across central NC this evening. High pressure will build into the region on Thursday and persist through Saturday. && .NEAR TERM /THROUGH TONIGHT/... As of 1055 AM Wednesday... The morning upper air analysis shows a large long wave trough over the central U.S. with a potent short wave ejecting from the Arkansas area northeastward into Illinois and Indiana associated with a 110kt jet at 500 hPa. Ahead of the trough, a deep and vigorous southwesterly flow is present across the Southeast transporting Gulf and even some Pacific moisture into the region with precipitable water values ranging from 1.3 to 1.5 inches. The latest surface analysis shows an eastward advancing cold front approaching the southern Appalachians. A band of showers and with embedded thunderstorms stretches from western PA southwest across WV into eastern KY and TN and then into AL from this morning. Thunderstorms as noted by total lightning data, stretch from southwestern VA into TN, and AL with a ongoing prefrontal QLCS from eastern TN into AL. Given the limited forcing for ascent across central NC, the latest regional radar shows virtually no precipitation across most of the state with a limited area of showers across the Carolina coast with the more significant band of showers just reaching the NC mountains. The vigorous flow aloft as noted by the 42kts observed at 2kft and 50kts at 2800ft on the 12Z KGSO sounding, will be mixed down to the surface at times today with routine surface gusts of 20 to 25kts. As the low stratus melts away and some breaks in the mid and high cloud deck develop, temperatures will warm into the 72-80 range by afternoon. The band of convection to our west will push east reaching the western Piedmont and Triad area between 22 and 02Z then spread east reaching the eastern Piedmont, Triangle, and Coastal Plain between 02 and 09Z. The SPC has our region outlooked in the a marginal risk for severe weather, largely driven by the vigorous wind field in a high shear/low CAPE environment. The primary limiting factor for severe convection remains the limited instability. Peak MLCAPE values generally range around 500 J/Kg although a pocket of higher instability, ranging from 500-1000 J/Kg may develop across the central and northern Coastal Plain in an area of higher dew points. In addition, the modest synoptic scale forcing with weak height falls and FGEN will not compensate for the limited instability. Finally, these parameters will become less favorable during the evening as the convective band approaches outside of peak heating and as the modest upper air features weaken with time. SHERBE values approach 1 near the frontal zone. Convection allowing models generally weaken the convection with time and eastward progress suggesting a more limited event that will still need to be monitored for locally damaging wind gusts. The weakening band of convection will slowly progress east this evening, slower than previously expected. All of the precipitation should clear central NC by daybreak. Slow clearing will arrive behind the front overnight. NAM and GFS BUFR soundings show a strengthening low level jet during the evening which could result in a local wind gust of 35+ MPH, even outside of convection. Temperatures will fall behind the front with lows by daybreak ranging from the upper 40s in the Triad to around 60 in the Coastal Plain where the front will just have cleared the area. -Blaes && .SHORT TERM /THURSDAY THROUGH SATURDAY/... As of 230 PM Wednesday... The synoptic cold front will have moved to the coast by 12Z tomorrow morning, with perhaps some early morning clouds giving way to sunny skies and cold air advection throughout the day. Models indicate low level thicknesses during mid afternoon about 50 meters down from Wednesday afternoon...which translates to 10-15 degrees cooler. As such, highs will edge above normal one final day...reaching around 60 northwest ranging to upper 60s in the southeast. Seasonable high pressure over the central plains will build eastward and the pressure gradient will relax Thursday night. Under clear skies with the cool dry airmass in place, mins will tumble into the 30s over the area, with some locations in the north and west potentially falling slightly below freezing near sunrise. Near zonal flow aloft and reinforcement of the surface high with modestly cooler air from the northern plains will maintain the status quo with mostly sunny skies Friday and increasing high cloudiness Saturday. Highs will be in the mid to upper 50s Friday cooling to the low and mid 50s Saturday. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
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As of 252 PM Wednesday... In the Sunday time frame...moisture advection out of the Gulf will stream east along a frontal zone setting up across the Gulf States. With a cool dry airmass in place, we should see a thickening cloudiness Saturday night with light rain breaking out due to isentropic lift in the west by mid day Sunday, and will maintain ongoing chance PoPs in the west during the morning spreading over the east during the afternoon. Highs will be subsequently suppressed by clouds and evaporative cooling, ranging from mid 40s in the northwest to lower 50s in the southeast. The forecast from Sunday night onward remains low confidence pending consensus as to the progression of a cutoff low over northern Mexico which will be lifting ENE across the plains early next week. Initially, the high pressure over the area is reinforced by the arrival of a second surge of cool dry air from a transitory surface high oriented more classically from New England south down the east coast, which would suppress moisture southward on Monday. This would set the stage for another isentropically induced rain regime on Tuesday/Wednesday as the moisture associated with the aforementioned cutoff low and associated surface reflection ride up the cooler denser air. Will keep PoPs on the low chance side for now, with highs in the 50s Monday through Wednesday as we wait to see how the scenario plays out.
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&& .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... As of 205 PM Wednesday... MVFR ceilings in a low overcast across the Piedmont have largely lifted with mainly scattered clouds at around 3kft and various BKN clouds layers above. Further east and south, the low overcast has been more stubborn with a predominance of BKN clouds at around 2.5kft. Mainly dry conditions with only isolated showers are expected this afternoon before an eastward advancing cold front pushes a band of showers and perhaps an embedded thunderstorm east across central NC during the evening and especially the overnight hours. The front`s eastward progress has slowed today. The best chances of showers along with ceiling and visibility restrictions range from 22Z to 03Z at the KINT and KGSO terminals and from 02Z to 08Z at the RDU/KRWI/KFAY terminals. Improving conditions with breaks in the overcast and clearing skies will arrive behind the front for the daybreak hours with VFR conditions in scattered cumulus clouds expected on Thursday. Gusty south winds today will become south-southwest this evening at 10-15kts with gusts of 20-30kts, even stronger in any thunderstorm. The winds will become westerly behind the front at 10kts and northwest at 10-15kts on Thursday. Looking beyond the 24 hour TAF period... High pressure will build into the region on Thursday and persist into Saturday resulting in fair weather. A storm system will approach the area from the southwest on Sunday with a chance of adverse aviation conditions late sunday into Monday. -Blaes && .CLIMATE... Record highs for 11/30 RDU 77 2006 FAY 80 1927 GSO 74 1991 Record high minimums for 11/30 RDU 62 1934 FAY 62 2001 GSO 62 1934 && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...BLAES NEAR TERM...BLAES SHORT TERM...mlm LONG TERM...mlm AVIATION...BLAES CLIMATE...RAH is the U.S. government's official web portal to all federal, state and local government web resources and services.