Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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531 FXUS62 KRAH 150855 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 355 AM EST Sun Jan 15 2017 .SYNOPSIS... A cold front will drop southward across central NC today. High pressure will build in behind the front and reinforce a cold air damming airmass over the area through Monday night. && .NEAR TERM /THROUGH TONIGHT/...
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As of 350 AM Sunday... Despite low clouds over VA and fog over SC, central NC is mostly clear this morning owing to westerly low-level downslope flow. There have been a couple periods of orographic cirrus just north of the VA border, but not enough to eliminate a small chance of some patchy fog around sunrise. Today: Given a lack of precip and diabatic enhancement of the CAD airmass the past day or so, the cold front over central SC this morning will continue to weaken under good heating today. However, a secondary cold front over central VA this morning will surge south into the norther Piedmont by midday and through all of central NC by early evening, as a 1032mb surface high shifts from the Midwest to the Mid-Atlantic states. As was the case on Friday (which today`s pattern seems to strongly resemble) the cold advection isn`t terribly strong and may lag the northeast wind shift by a few hours. The front should induce some low-clouds between 2-4k ft, especially in the coastal plain per NAM/GFS forecast soundings, but the flow is pretty weak throughout the low- levels, so it`s hard to see widespread stratus until later tonight. Highs should feature a large range from north to south again, as the over all lack of greater cloud cover will allow for good heating, specially across the south through early afternoon. Most guidance suggests 50-65 for highs, though the RAP/HRRR has highs of 70 in the southern Piedmont. Tonight: The cold front will push south of the area by this evening, with weak cold advection and a light northeast wind overnight. The H9 flow will swing around to southerly after midnight, resulting weak (and shallow) isentropic lift in the western Piedmont. As a result, some patchy light rain or drizzle should break out and drift east through the Piedmont through Monday morning, with low clouds eventually engulfing the entire area. Lows 38-45.
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As of 350 AM Sunday... CAD will persist Monday as the parent surface high shifts to the Mid-Atlantic coast and then eventually offshore. The main impacts look to be from just widespread low clouds since the H9-H85 flow is weak (< 30kt) and the flow aloft is flat. Low clouds will result in highs several degrees cooler than today, but the lack of precip should keep highs within a couple degrees but on the cooler side of guidance; 45-52. The aforementioned surface high will shift offshore Monday night, but our CAD airmass should linger without an erosion mechanism. Warm advection will start to increase over the western Piedmont, on the eastern flank of a prefrontal LLJ over the Tenn Valley. Most of the associated rain will be west of the mountains, but their could be a few areas in the Foothills and flirting with the western piedmont by Tuesday morning. Lows 42-46.
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 300 PM Saturday... A 1030-1032 mb surface high will settle over the New England coast Monday resulting in a CAD wedge over northern and western NC. The high will shift off the Mid-Atlantic coat Monday night, but the wedge will remain over northwest portions of the area through Tuesday, as the return flow from the high offshore and increasing southerly flow ahead of the approaching front won`t erode it before then. Meanwhile aloft, the closed low over the Baja will swing northeast into the Midwest by Monday and toward the Great Lakes through Monday Night. The aforementioned low will get absorbed in the northern stream Tuesday while a lingering trough/low remains of the southwest U.S. The strength of the low/shortwave as it moves through the Great Lakes and the high ridging over the southeast U.S. will play an important part in how the weather plays out over Central NC Tuesday through Thursday. It is even uncertain at this time when the actual frontal passage will occur. Given all the uncertainty, the forecast confidence is very low at this time, with respect to both temperatures and precipitation. The secondary southern stream low will progress eastward Thursday through Saturday as a strong upper low approaches the Northwest U.S. coast, digging a very deep trough over the western U.S. Although confidence is low, it does appear that another round of precipitation will occur as the low moves eastward in the Mid- Atlantic late in the week/early weekend, but exactly when and how much is far to uncertain to specify at this time. && .AVIATION /08Z SUNDAY THROUGH THURSDAY/... AS OF 1250 AM Sunday... Pretty high confidence in VFR early this morning, with clouds at 6- 8k ft drifting east across the area and a chance of MVFR/IFR vsbys between 09z and 12z, especially at FAY. A cold front will surge south across the area between 15z and 21z today, causing the currently light and variable winds to become northeasterly at 6- 10kt. Models have struggled with this weather pattern the last couple of days, and seem to still be in disagreement on how quickly MVFR ceilings will redevelop, but recent trends suggest some scattered MVFR ceilings this afternoon and then a better chance of cigs lowering at FAY/INT/GSO/RDU after 00Z. RWI may stay VFR through the period. Outlook: Conditions are expected to at least MVFR by 12Z Monday, and more likely IFR at INT/GSO, as southerly flow reinforces a cold air damming airmass over the area. Low cigs should persist into Tuesday, when there will be a chance for low clouds to scatter ahead of a cold front approaching from the west. The cold front and associated rain and low cigs/vsby will should impact the area Wednesday. VFR Conditions will return to all terminals in the wake of the cold front Wed night and Thursday.] && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...SMITH NEAR TERM...SMITH SHORT TERM...SMITH LONG TERM...KCP AVIATION...SMITH is the U.S. government's official web portal to all federal, state and local government web resources and services.