Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 090833 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 333 AM EST Sat Dec 9 2017 .SYNOPSIS... A strong upper level trough and surface cold front will cross the region today. High pressure will follow the front for Sunday into Monday. An arctic front will push through the area Tuesday night, bringing frigid conditions for mid week. && .NEAR TERM /today through tonight/... As of 310 AM Saturday... No changes to the existing warning/advisory at this time. We remain in a relative lull, with precip largely absent over the last few hours west of Highway 1, and rain has decreased in coverage and intensity from Highway 1 east in the last few hours. But this will gradually be supplanted by the band of precip now extending from the SW mountains of NC to the SW across N GA, E/S AL, to the W FL panhandle. This appears to be largely driven by mid level DPVA, as a potent vort max tracks NE on the E edge of the mid level trough axis, and upper divergence in the right entrance region of the 170- 180 kt jet streak. Recent high res model runs, including the HRRR (which has done well in recent runs) and HREF, along with traditional models, all show this precip band (consisting primarily of snow, as suggested by the cold thermal profile, which will be cooling further aloft this morning) spreading NE over the NC mountains and foothills into the NW Piedmont this morning. The tail end of the band is then likely to sweep ENE across the rest of the W and N Piedmont through the afternoon, following the mid level vorticity lobe. As this shifts east through the region, drying aloft (above -10C) will ensue by mid afternoon, followed by a backing of the 925-850 mb winds to northwesterly late this afternoon, yielding downslope drying and finally allowing for a diminishing of precip. Models suggest that the NW Piedmont (particularly along/NW of the I- 85 corridor) could easily see another two tenths to a quarter inch of liquid equivalent with this band. And based on upstream totals with this band so far, these totals may be on the low side. It`s also concerning that as we start to cool aloft (evident on 700 mb progs), snow ratios are expected to increase, up to 8:1 or 10:1 late morning into midday. We currently expect additional snowfall to range from around a half inch in the Triangle to around 2 inches N near Roxboro and WNW in the Triad area. Some of this precip may be more of a rain/snow mix from Albemarle to the Triangle to Warrenton, and there may be a little sleet mixed in from the time to time through this corridor. There is a small chance that additional snow fall will be closer to 3 inches in the Triad region, and a very good chance of at least an additional inch there. With a developing low level downslope flow late and a generally drying trend through the column, we should see clearing from WSW to ENE by this evening. But the passage of a strong vort max diving into the trough base, from the upper Midwest through IL/IN and TN before crossing the far S Appalachians and NC tonight, will likely bring a few clouds and perhaps a flurry through the Sandhills and central Piedmont. But moisture will overall be too low for anything more than that. Earlier forecast of very cold highs today is supported by the latest guidance, which shows temps holding in the 30s over all but the far SE sections. And portions of the far N Piedmont may only get a couple of degrees above freezing. Expect chilly lows tonight of 22- 27. -GIH && .SHORT TERM /Sunday through Sunday night/...
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As of 330 AM Saturday... Mostly sunny but chilly. We`ll be undergoing deep subsidence but will stay in a fairly fast WNW cyclonic steering flow, which will draw a series of waves swiftly through NC. A broad and sheared disturbance will pass through in the morning with little fanfare, then a second more potent wave will cross the area during the late afternoon. Finally, the strongest of these features will track along the NC/VA border Sun night. In each case, the column is quite dry, although the last perturbation Sun night should bring a batch of mid clouds across the area overnight. With continued cold air advection and much below normal thicknesses, expect highs from the upper 30s to mid 40s Sunday. Lows again should be about 22-27. -GIH
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&& .LONG TERM /MONDAY THROUGH FRIDAY/... As of 255 AM Saturday... Fairly low amplitude pattern to begin the long term forecast which will lead to a period of cool but quiet weather to begin the week. This will lead to slightly below normal high temperatures Monday and Tuesday with highs in the middle 40s north and west to mid 50s south and east and lows Monday night in the upper 20s to low 30s. Tuesday night will be a different story however as a clipper system moves through the Great Lakes and a longwave trough digs southward pushing a dry cold front through the area Tuesday night. This will plunge overnight lows into the upper teens to mid 20s across central NC. Strong cold air advection continues on Wednesday during the day as highs will struggle to get out of the low 30s across the northern tier of counties with closer to 40 degrees in the south. This comes in about 15 degrees below normal for mid-December. Only slight moderation for Wednesday night with lows generally in the lower 20s. For the end of the week, there will be a slight warmup during the daytime hours with highs in the low 40s to low 50s north to south but overnight lows will still register below freezing in most locations. The only chance for precipitation comes on Friday as a second clipper system moves across the mid-Atlantic with central NC flirting with the left exit region of a strong upper jet. This could produce some snow showers across the VA border counties, but it is too early to tell if the dynamics will line up just right. In addition, there isn`t a lot of available moisture available so any snow would be of little to no impact. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... As of 105 AM Saturday... 24 Hour TAF Period: Widespread precipitation will affect the region through mid day, before ending from southwest to northeast during the early to mid afternoon. A brief lull in precip across western NC has resulted in ceilings lifting to VFR and MVFR currently, but ceilings will lower between 06 to 12z as precip fills back into the area, with generally IFR/LIFR cigs. MVFR Visibilities will lower to IFR during heavier precip. With regard to P-type, light freezing rain/drizzle at KINT and KGSO will transition to a mixture of sleet and snow, with mostly rain expected elsewhere. KRDU and KRWI could see a brief change over to snow early Saturday afternoon, before ending. VFR conditions are expected to return Saturday night as dry air spreads in wake of the coastal low tracking up the Mid-Atlantic Coast. Outlook: Dry VFR conditions are expected Sunday through mid week. && .RAH WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning until 4 PM EST Saturday for NCZ007>009-021>024- 038-039. Winter Weather Advisory until 4 PM EST Saturday for NCZ008>010-025- 026-040-041. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield SHORT TERM...Hartfield LONG TERM...Ellis AVIATION..CBL

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