Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 140756 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 255 AM EST Thu Dec 14 2017 .SYNOPSIS...
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A weak and dry surface cold front will push south through the area today. An area of low pressure will develop along the NC coast Friday, then tracks northeast while staying offshore Friday night. High pressure will build into the area through Sunday.
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&& .NEAR TERM /THROUGH TONIGHT/... As of 935 PM Wednesday... WV satellite and 00Z upper air data depict a lead shortwave trough beginning to lift enewd to newd into swrn PA, while a trailing shear vorticity-dominated one centered invof srn Lake MI was digging across the lwr Great Lakes and toward the OH Valley. Related to the lead trough, a narrow band of DCVA/forcing for ascent --and an associated, approximately 100 mile wide axis of mid level moisture now over the NC Piedmont, and centered around 10 k ft per surface observations and 00Z GSO and RNK RAOB data-- will pivot east across e-cntl NC through 05-06Z. In addition, strongly veering flow through the lowest couple of kilometers (WAA) --and implied forcing for ascent-- was evident throughout the lwr OH Valley, srn middle Atlantic, and Southeast. A band of precipitation, mostly in the form of snow, not coincidentally was pivoting newd within a zone of strong QG-forcing for ascent accompanying the lead shortwave trough and preceding strong lower tropospheric WAA - a truly textbook case of QG-theory at work. At the surface, a parent, 993 mb cyclone was analyzed over far nwrn OH at 02Z, with a preceding warm front analyzed sewd from the low - across cntl OH and the VAs and on the srn flank of the aforementioned precipitation band. To the south of the warm front, sly to swly low level flow exists in the warm sector over the Carolinas. Light radar returns have steadily lowered, to about 2000 ft in a narrow, approximately 10 nm wide arc between IGX and RDU in the past hour. Although extremely narrow, and originating from the aforementioned narrow band of ceilings centered well above the surface - around 10 k ft (between 8-13 k ft per KRAX data), a 5-10 minute period of a few flurries may reach the surface as the parent moist axis shifts ewd. Otherwise, a strong swly to wswly llj evident on the RTP profiler, between 30 and 45 kts at 2 and 5 k ft, respectively, will occasionally mix to the surface and manifest as gusts up to 25 mph, as has already been the case across several Piedmont sites in the past couple of hours. Given that WAA is occurring in that layer, which will promote stability, it is likely that at least temporary surface decoupling and lessening of the surface wind to 5-6 kts or less will allow temperatures to dip into the middle 20s to around freezing by daybreak - about 10 degrees from 9 PM readings. && .SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
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As of 300 AM Thursday... The next shortwave in the broad cyclonic flow aloft, will dive SE through the Northern and Central Plains today and into the Carolinas on Friday, becoming increasing sheared by the energetic split flow regime across the Conus. With the approach of this next wave and attendant upstream height falls, a weak area of low pressure will develop near the NC coast, along the old frontal zone. While limited moisture will keep the forecast dry, central NC could see a good mixture of clouds and sun on Friday, with highs ranging from from lower to mid 40s north to lower 50s SE. As the coastal low tracks NE out into the Atlantic, surface high will build east into the area Friday night. Lows in the mid 20s to around 30.
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&& .LONG TERM /SATURDAY THROUGH WEDNESDAY/...
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As of 225 AM Thursday... Saturday and Saturday night will be dry over Central NC with temperatures just a few degrees below normal for mid-December as surface high pressure builds over the area and west-northwest flow dominates aloft. The surface high will shift offshore on Sunday as a warm front lifts northward through the area Sunday eve/night. Meanwhile, a shortwave aloft lifts east-northeast out of the ARKLATEX toward the Northeast riding the northern periphery of the upper level ridge extending into the Carolinas from the parent high over the Caribbean. Latest model solutions indicate any precipitation with this system should skirt north of the area Sunday night. However, the strong south-southwesterly flow into the region behind the aforementioned warm front will advect warm, moist air into the Southeast and Mid-Atlantic resulting in increased chances for rain, especially further south, on Monday. Beyond Monday the medium-range models diverge significantly with respect to the upper level pattern. Given the large spread in solutions, wide range of forecast possibilities, and low forecast confidence, will carry at least a slight chance of rain through Tuesday. The 00Z Thursday model solutions are in slightly better agreement than the 12Z Wednesday ones, so hopefully that trend will continue with an increase in forecast confidence for Tuesday and Wednesday. Temperatures will increase from Sunday through Tuesday to several degrees above normal, decreasing on Wednesday.
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&& .AVIATION /00Z THURSDAY THROUGH MONDAY/... As of 1230 AM Thursday... There is a high probability of VFR conditions across central NC through 00Z Friday. A fast moving upper disturbance continues to the east at this hour, leaving the northern piedmont under clearing skies and a brisk Northwest wind. An attendant sfc front will cross central NC later tonight through early Thu. This system will be accompanied by a deck of mid level clouds with ceilings at or above 10000ft. These clouds will depart prior to sunrise Thu. Low level wind shear is also a concern in the proximity of KFAY and KRWI as winds just a couple thousand feet above the surface will be swly 35- 40kts for a short period of time. VFR conditions are expected to continue through Saturday night. Another area of low pressure will affect our region late Thu night through Friday. Ceilings associated with this system are expected to remain VFR. A low pressure system approaching from the west may bring a threat for sub VFR ceilings to central NC late in the weekend. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...CBL NEAR TERM...MWS SHORT TERM...CBL LONG TERM...KCP AVIATION...WSS/JJM

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