Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 301131 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 630 AM EST Wed Nov 30 2016 .SYNOPSIS...A cold front will cross the area this evening through early Thursday. Behind the front, high pressure will build into the region over the remainder of the week. && .NEAR TERM /Through Tonight/...
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As of 355 AM Wednesday... A deep trough remains in place over the central US this morning, with deep, moist southwesterly flow over the Southeast US. The primary synoptic cold front stretches from Lake Michigan to southern Louisiana, with an effective front and ongoing prefrontal QLCS from southern Mississippi to the Tenn Valley. Locally, a band of spotty light showers lifted through the area late last night, with a lull in precip now. This will likely continue for a good portion of the day given fast but uniform southwesterly flow aloft. 40kt winds near 2000 ft, per NAM and GFS soundings, will result in wind gusts as high as 28-32kt as mixing heights increase, and all indications are that mixing won`t be terribly inhibited by the low stratus that has redeveloped in the Piedmont this morning. A warm and breezy south wind should blow this away and result in near record highs some 15-20 degrees above normal; 71-80. Potential for strong or severe storms tonight: A pronounced shortwave and speed max within the base of the upper trough will eject northeast across the Tenn Valley today and this evening, followed by the cold front overnight. A 50-60kt LLJ will again translate across the region this evening. The QLCS to our west will reinvigorate across the deep South with heating today, and the big question is whether or not any severe weather will unfold in a classic high shear/low CAPE environment. Weak instability, maybe 500 J/KG, may develop given warm sector dewpoints easily in the 60s this evening, but low and mid level lapse rates are forecast be weak, and height falls will be relatively weak (~40m) as the shortwave shears a bit crossing the Tenn Valley. Thus, we don`t really get a strong shot of DCVA and associated upper forcing to help overcome the lack of instability, and FGEN is also forecast to weaken with eastward extent tonight. SHERBE values approach 1 along and east of US-1 after 00Z, but the overall lack of instability to overlap with the LLJ and 60-70kt mid-level flow make it hard to imagine much more than a few broken bands with isolated storms, some of which could certainly still tap into 40-50kt winds. SPC has retained the Marginal Risk for today, and that seems to fit with the uncertainty in instability and potential for near storm destablization. Whatever band of convection will get should be east of I-95 shortly after midnight, with drier westerly winds behind the front and temps falling into the upper 40s west to mid/upper 50s east.
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&& .SHORT TERM /THURSDAY THROUGH SATURDAY/... As of 350 AM Wednesday... The synoptic cold front will have moved to the coast of NC by 12Z Thu, while a trailing surface trough will linger from Srn NC WSWwd into Wrn SC throughout the day. Moisture cross sections suggest stratocumulus may linger along this axis, across the Srn Coastal Plain and Sandhills. Deep subsidence behind the lifting parent shortwave trough suggests a sunny sky is expected otherwise and elsewhere. It will be the transition day for temperatures, from near record warmth on Wed to near average on Fri. High pressure will extend from the Plains to the Central Appalachians throughout the period, with just weak reinforcing cold frontal passage, heralding a change in wind direction from WNW to NNE, late Fri-early Sat. Lows both nights in the 30s, though some upper 20s will be possible as the center of the ridge nears, behind the aforementioned reinforcing front with low level thickness values around 1305-1310 meters, Sat morning. && .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... As of 400 AM Wednesday... The medium range remains riddled with forecast uncertainty regarding how quickly a cutoff over the SWrn U.S. and Nrn Mexico gets kicked ENEwd through early next week. Similar (to previous days) model differences exist, with a faster progression indicated by the deterministic EC, and a slower one by the GFS. In either case, a merged/phased Srn and Nrn branch jet to the E of the cutoff low will stream NEwd into the Ern U.S. and result in a lowering high and mid level OVC, late Sat night-Sun, which favors cooler than previously forecast temperatures for Sun - mostly 40s to lower 50s. A wide range of forecast solutions will exist Sun onward, none of which can be favored with any accuracy at this time. So while it does appear some meaningful rain will fall, it remains unclear exactly when between Sun-Tue. && .AVIATION /12Z Wednesday Through Sunday/...
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As of 630 AM Wednesday... Confidence is high that ceilings will improve during the day, though the timing of MVFR or VFR being reached is still uncertain. Moist southerly flow continues this morning ahead of a cold front moving through the deep south. MVFR and IFR ceilings at GSO/INT/RDU will persist through mid morning, with ceilings expected to lift the MVFR at GSO and INT, and VFR at RDU by this afternoon. Meanwhile,satellite imagery suggests the current VFR conditions at RWI/FAY may still fall to IFR before 15z, with VFR then expected to prevail through the afternoon. As ceilings lift and mixing deepens, southerly winds wind increase to near 15kt, with gusts to near 30kt possible. The cold front and a strong line of storms will be approaching from the west this evening, and is expected to move east across central NC between roughly 22Z and 05Z. The line should lose some of its vigor with time, but a few strong storms and gusts to 40-45kt are possible, along with heavy rain and very low ceilings/vsbys. A west wind will develop after 06Z as the front moves through the area, and VFR conditions will redevelop. Outlook: High pressure with fair weather is expected for Thursday into Saturday. A storm system will approach the region for Sunday with a period of adverse aviation conditions.
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&& 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...KDS NEAR TERM...Smith SHORT TERM...MWS LONG TERM...MWS AVIATION...Smith CLIMATE...RAH

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