Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 251156 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 756 AM EDT Wed Apr 25 2018 .SYNOPSIS... An upper level low, and related surface low pressure system, will track northeastward across central NC and southeastern VA early today. A weak cold front will then cross our region late this afternoon and tonight. && .NEAR TERM /THROUGH TONIGHT/... As of 400 AM Wednesday... A mid-upr low, and associated cold pool aloft characterized by 500 mb temperatures around minus 18C over the wrn Carolinas this morning, will devolve into an open wave while lifting newd, to near the Chesapeake Bay by this evening. Several perturbations embedded within the low, including a lead one now centered over CLT per WV satellite imagery, will rotate in negative tilt fashion across cntl and ern NC through 18-21Z today. At the surface, an occluded/wedge front was analyzed at 08Z from a 1006 mb low centered near EXX, enewd to near RDU and ECG. This low will will wobble very slowly enewd across n-cntl NC and sern VA today, while becoming increasingly vertically-stacked directly beneath the aforementioned upr feature. Mixed character rain/showers, within and immediately ahead of the upr low, will spread slowly enewd across cntl NC through 20-21Z, with the greatest concentration along the track of the mid level deformation maximum and cold pocket aloft - roughly along and north of US Highway 64. The mixed character of the precipitation will evolve from predominately stratiform to predominately convective, with diurnal heating and diabatic contribution to destabilization after 14-15Z. While several lightning strikes have already occurred near Concord within the last couple of hours, with similar development expected across the wrn Piedmont as the upr low moves overhead this morning, the models suggest as much as 500-1000 J/kg of MLCAPE will materialize over the ne NC Piedmont and nrn Coastal Plain by 18Z. There, small hail will likely accompany the convection given low freezing and wet bulb freezing levels between 8000-9500 ft. Additionally, modest swly mid level flow aloft --around 30-40 kts on the ern periphery of the devolving mid-upr low-- will favor mid level rotation and a risk of severe hail from near RWI and IXA ewd to the nern NC coast. Otherwise, it will be a mostly cloudy day for most, though with some clearing probable over the srn Piedmont, Sandhills, and srn Coastal Plain both late this morning, before "self destructive" sunshine beneath the cold pool aloft causes cloud redevelopment, and again late this afternoon as the cold pool aloft and deformation moist axis move enewd. While drier air will steadily infiltrate cntl NC in wly/nwly flow behind the passing occluded low today, a secondary cold front --and surge of cooler and drier air-- now stretching across the upr Midwest, will collapse east of the cntl Appalachians and into cntl NC overnight. Skies will clear with the onset of nocturnal cooling by this evening, but with thickening mid level cloud cover late tonight downstream of a kicker trough aloft amplifying now across the cntl High Plains. Lows generally in the lwr to mid 50s are expected, with some upr 40s possible where winds go calm, as the pressure gradient relaxes late. && .SHORT TERM /THURSDAY THROUGH FRIDAY/... As of 350 AM Wednesday... A dry backdoor cold front will briefly sag south in the wake of the departing low as it lifts north into New England. This front will stall across the northern tier of central NC, stalling highs in the the upper 60s north, while the southern tier will reach mid 70s. The front will be quickly lifted back north of the area ahead of a vigorous southern stream closed low which will be moving east across the southern Plains into the Tennessee Valley Thursday night. This low will be accompanied by a rather impressive elevated mixed layer featuring mid level lapse rates of 6-7 K/km and at least modest upper diffluence complements of a 90Kt jetlet. Showers and scattered thunderstorms are expected to break out Thursday evening in the western Piedmont, with coverage increasing as the system lifts northeast up the Appalachians. As such, will raise PoPs to likely (~60%) category and transition the PoPs from the western Piedmont Thursday evening into the east after midnight. Activity will quickly taper off to scattered Friday morning as the system lifts northeast and is absorbed into the larger scale long wave trof migrating into the eastern CONUS. Should see some breaks in cloudiness on Friday with highs reaching low to mid 70s after mild morning lows in the mid 50s. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... As of 350 AM Wednesday... The longer range outlook is dry with a welcome warming trend on track to arrive early next week. A long wave trof will edge east across the Atlantic coast early this weekend, with cool air reinforced by a modest cold front Saturday night as the trof axis moves east of the area. Highs Saturday through Monday will be mostly 70 to 75 after morning lows mostly in the upper 40s. Surface high pressure will settle overhead on Monday as mid level ridging over the Plains begins moving east to produce height rises and warming early in the week. Stacked ridging will produce near-cloudless skies Tuesday and Wednesday with highs rising from upper 70s Tuesday to lower 80s on Wednesday. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... As of 750 AM Wednesday... Widespread IFR-MVFR conditions this morning, most pervasive from the Triad (INT/GSO) enewd to near RDU and RWI --in a residually cool/stable/saturated cold air damming air mass situated to the north of a nearly stationary/occluded front analyzed at 12Z from near VUJ to RDU to ORF-- will gradually improve to VFR from west to east later today. This scattering and lifting to VFR will occur as drier wly/nwly filters into our region behind an area of low pressure, analyzed at 12Z near IGX, which will track slowly newd along the aforementioned front. Otherwise, an upr level low and associated cold temperatures aloft will track directly over cntl NC through mid afternoon. Showers will accompany the passing upr lvl low; and some storms with small hail will also likely result as diurnal heating/destabilization occurs after 15Z centered around the RWI/IXA/ASJ vicinity, beneath the aforementioned cold temperatures aloft. Outlook: An upr level trough and related surface low pressure system will track newd across the Carolinas Thu night. A period of sub-VFR conditions, showers, and a chance of thunderstorms, will result during that time. && .RAH WATCHES/WARNINGS/ADVISORIES... NC...None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...mlm LONG TERM...mlm AVIATION...MWS

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