Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 222348 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 648 PM EST Sun Jan 22 2017 .SYNOPSIS... A potent low pressure system will track northeast from the Deep South into the Carolinas tonight, linger over the area on Monday, then track off the Mid-Atlantic coast on Tuesday. && .NEAR TERM /THROUGH TONIGHT/... As of 330 PM Sunday... Less severe threat than previously expected tonight... The upper low is currently over the Lower Miss Valley region, while the associated surface low pressure appears to transitioning from the earlier ArkLaTex to a dominate low over AL. Still expect intense deep layer lift as upper diffluence and DCVA increase rapidly after 00Z and a 50kt LLJ translates east across SC/GA. The QLCS will getting going over southwest GA and the FL Panhandle this afternoon will expand north toward the Carolinas this evening. The biggest question in central NC continues to be the northward extent of the warm sector and efficiency of CAD erosion before QLCS arrives, which is not looking favorable for the severe weather. The wedge front has retreated into the southern CWA, though destablization has been hindered by convection blow off from the overnight convection in southern GA and weak moisture transport so far. The true warm sector is still suppressed way south over southern GA by the aforementioned high clouds and diabatic effects of morning convection. By all accounts, the warm sector will never reach the Piedmont and may even struggle to extend into the southern Coastal Plain before being swept out by the cold/occluded front. Most guidance suggests a narrow corridor of ~500 J/KG of MUCAPE that may stay slightly elevated east of US 1, and even HRRR simulated reflectivity is rather unimpressive. As such, current thinking is the best threat of strong storms is southeast of a line from Laurinburg to Fayetteville to Goldsboro between 01Z and 05Z. The main segment of convection will be departing after midnight, but the threat of showers and isolated storms may continue from the southwest overnight as the upper low wobbles toward the area. Deep layer shear 60-80kt and 200-400 J/KG of MUCAPE, owing to 7 C/KM mid-level lapse rates rounding the upper low, may still support some elevated cells in the Piedmont and a small hail threat between 06-10z as the occluded front pushes north through the area, but even that looks questionable. Temps should hold mostly steady across the north and rise a little into the mid 60s in south this evening, and then rise later tonight with mixing associated with the occluded front. && .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/... As of 400 PM Sunday... A mean mid to upper level low --one consisting of at least three distinct vortices over AL, LA, and AR, and associated pocket of steep lapse rates/cold temperatures aloft characterized by 500 mb temperatures of minus 22-24C-- is forecast to wobble across the Gulf coast states this evening, then lift NEwd into SWrn NC by 12Z Mon, and off the VA coast by 12Z Tue. An associated 998-990 mb surface low will likewise migrate across Srn and Ern NC during the day Mon, and up the Middle Atlantic coast Mon night, while the preceding occluded front --near the VA border at 12Z Mon-- will pivot Nwd into VA. Sensible weather: Early day partial sunshine over the NE Piedmont and Coastal Plain will yield to cloudy or mostly so skies that will pivot ENEwd with the aforementioned deep layer/occluding cyclone. While scattered "instability" convection will be possible throughout central NC, as weak instability of up to several hundred J/KG develops with diurnal heating (into the middle 50s W to lower 60s E) amidst marginal surface moisture characterized by 45-50 F dewpoints, and beneath the cold pool aloft, convective coverage and intensity will be relatively maximized from the Sandhills to the Ern Piedmont and Coastal Plain, where QG-forcing for ascent ahead of the cyclone will best overlap with early afternoon heating. Both lightning and small hail/graupel will probably accompany the convection here, with lesser chances of each elsewhere. No severe weather is expected, given very weak forecast wind fields as the center of the cyclone passes overhead, and too-limited instability to support anything but small hail. While SW to NE clearing will take place overall Mon night, as the low lifts away, a band of deformation-type low clouds may wrap SEwd from near Roxboro to Goldsboro and points Ewd through early Tue morning. Lows mostly in the lower to middle 40s. && .LONG TERM /TUESDAY THROUGH SUNDAY/... As of 220 PM Sunday... Tuesday and Wednesday: Any lingering cloudiness Tuesday morning will be retreating rapidly to the northeast as the coastal low lifts up the mid Atlantic coast. Unseasonably mild temperatures will stay with us through mid week with copious sunshine and increasing heights as mid level ridging migrates across the area. Highs on Tuesday will range from the upper 50s north to lower 60s south, warming on Wednesday to the mid and upper 60s. A strong shortwave lifting out of a longer wave trof into the Great Lakes region will push a cold front across the mountains Wednesday night and rapidly east across central NC and out of the area by mid afternoon Thursday. This front will be accompanied by scattered showers and begin our transition to north west flow and attendant cooler temperatures for late week and through the upcoming weekend. Temperatures on Thursday will have time to warm to the mid 50s west to lower 60s east before the cooler air arrives, and we will really notice the end of our two week mild spell Thursday night as mins fall to near freezing in the northwest to mid 30s elsewhere. Northwest flow will produce dry, but much cooler conditions Friday through Sunday, with highs in the 40s each day. Mins Friday and Saturday night will range from 25 to 30. && .AVIATION /00Z MONDAY THROUGH FRIDAY/...
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As of 645 PM Sunday... 24-Hour TAF period: Another area of rain is lifting northward into Central NC and will continue to move through the area through 12Z or so Monday morning. Chances for thunder continue to diminish, though there is still a chance, albeit fleeting, at KFAY and less so at KRWI. Aviation conditions will largely remain IFR/LIFR through tonight, with possible slight improvement while rain is occurring. Also, winds may also get gusty in the stronger showers/storms, but otherwise will be 10-12 kts, decreasing Monday morning. Conditions should improve to MVFR/VFR after 12Z Monday, though another round of rain is possible as the low swings through the area Monday afternoon and could reduce cigs again as it does so. -KC Looking ahead: Conditions are expected to improve /return to VFR/ sometime late Monday night or early Tuesday as the aforementioned system tracks offshore the Carolina/Mid-Atlantic coast. A cold front will cross the region by Thursday and may bring some adverse aviation weather. -SMITH
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...SMITH NEAR TERM...SMITH SHORT TERM...MWS LONG TERM...MLM AVIATION...KC/SMITH

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