Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 070112 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 812 PM EST Tue Dec 6 2016 .SYNOPSIS...
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Low pressure will move away from the Middle Atlantic coast tonight. Weak high pressure will follow and settle over the Carolinas through Wed night. An arctic cold frontal passage will occur on Thu.
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&& .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... As of 330 PM Tuesday... A slowly deamplifying shortwave is currently crossing the northwest Piedmont, with significant drying aloft noted on water vapor across all of central NC. Plenty of low-level moisture remains in the CAD airmass entrenched over the Carolinas, though visible satellite imagery is showing signs of westerly low level flow and drying in the lee of the mountains. A surface low was analyzed off near Care Fear this afternoon, with the CAD boundary extending across SC into central GA, and then back north as an occluded front to a low over the OH Valley. Patchy showers associated with the upper wave and some weak MUCAPE atop the cold dome are moving off to the northeast and should be out of the northern Piedmont/Coastal Plain by 21-22Z. The main forecast problem for this evening is top down drying and the potential for dense fog. Drying aloft and a weak pressure gradient in the wake of the departing low pressure system support the notion of dense fog, at least for a period tonight. Surprisingly, the HRRR doesn`t show much fog (shows lower vsby across SC) and forecast soundings show dry air advection from the west eroding the lingering stratus without much fog. Still think fog will be possibly across portions of the central Piedmont and Coastal Plain, but confidence is not high enough for a dense fog advisory at this time. Temps may settle a few degrees into the upper 30s and lower 40s. && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... As of 230 PM Tuesday... The leading edge of an arctic cold front diving southeast through the TN/OH valley begins to ooze across the Appalachians by 12Z Thursday morning. The front will be progressing slowly as it aligns with predominantly westerly flow, which will also serve to limit moisture advection available for precip. Forcing aloft will be limited as well in relatively broad cyclonic flow and channeled vorticity, with models squeezing out less than a tenth of an inch of rain with the system. As such will maintain only a small chance for PoPs as the front moves through during the day. Skies should be clearing from the northwest by mid to late afternoon. Cold air advection will be underway for much of the day across the northern tier with northwest winds 10 to 15 mph gusting 20 mph. This produces a low level thickness fall of ~20 meters across the north... indicative of 5-6 degrees cooler temps...resulting in highs from the low 50s across the north to upper 50s in the south. Pressure gradient relaxes overnight, but not enough to decouple and fully realize the airmass` potential for cooling. Mins should bottom out in the mid to upper 20s. && .LONG TERM /THURSDAY THROUGH TUESDAY/... As of 230 PM Tuesday... Expect clear, cold, and brisk conditions on Friday with highs in the upper 30s to lower 40s with a northwest breeze gusting to 20 mph. Radiational conditions are more ideal Friday night as an arctic high settles over the region. Mins will fall into the upper teens across the north to lower 20s in the south Saturday morning. Chilly airmass will benefit only marginally from strong but low-angle insolation on Saturday...with highs ranging from 40 to 45. Return flow will ensue on Sunday, with modest warmup and initiation of some moisture advection and cloudiness. Highs will edge to the mid and upper 40s on Sunday after morning mins mostly in the mid 20s. Our next frontal passage on Monday will be better defined/cleaner. With the mid level short wave and parent surface low well north of the area we maintain near zonal flow behind the front to inhibit cold air advection. Does look like a respectable low level jet and convergence zone will accompany the front resulting in chance PoPs Sunday night through Monday afternoon with clearing by Tuesday. Highs in the 50s both Monday and Tuesday. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
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As of 810 PM TUESDAY... Low pressure near VA Beach will move away from the Middle Atlantic coast tonight. A drying WNW flow behind the departing low will cause ceilings to initially lift to MVFR and/or scatter during the next several hours. However, a weak area of high pressure and associated light to calm wind will settle overhead overnight, which in conjunction with clearing aloft and wet soil, will lead to the development of fog (and associated vertical visibility restrictions/ceilings). While the coverage and degree of restrictions remains unclear, the lowest visibility/ceilings appear most likely to occur at INT and GSO, where the aforementioned lifting and scattering of the preceding low clouds has, or will very soon, occur. ANy fog and low clouds will quickly disperse Wed morning, with the exception of over Ern VA and NErn NC (centered near ECG), where a band of low clouds may linger through midday to early afternoon. This band of low clouds is expected to hold just to the E of RWI, though it may edge briefly into the vicinity there Wed morning. Outlook: A warm front will lift into NC and result in a good chance of MVFR ceilings Wed night-early Thu, especially at Ern TAF sites, followed by a small chance of a shower along an arctic cold front during the Thu, and following blustery NW winds late Thu afternoon- Thu night.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...SMITH SHORT TERM...MLM LONG TERM...MLM AVIATION...MWS

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