Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 250544 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 145 AM EDT Sun Mar 25 2018 .SYNOPSIS...
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An area of low pressure will exit off the North Carolina coast early this morning. Chilly high pressure will build into the Carolinas from the north through Tuesday. This high will drift offshore Wednesday, leading to a sly return flow and initiating a warming trend.
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&& .NEAR TERM /TONIGHT/... As of 1020 PM Saturday... A Winter Storm Warning has been issued for areas along and northwest of Interstate 85, for a heavy, wet snow accumulation of 1-3 inches, with locally near 4 inches. The highest amounts are expected to occur over the nrn portions of the warned counties, with a sharp gradient in accumulation and much lighter amounts over the srn portion of those counties. A Winter Weather Advisory has been expanded to include Davidson, Randolph, Chatham, Wake, Franklin, Warren, and Vance Co., where a similarly sharp gradient of accumulation from just a Trace to one half or one inch can be expected, mainly on elevated and grassy surfaces. Strong and coupled QG and mesoscale forcing for ascent will maximize over cntl NC through 06-09Z, related to a deamplifying and increasingly elongated mid-upr wave now stretching from the lwr OH Valley to the upr Midwest, and strong WAA and Fgen centered at 850 mb, within and atop a sharp low level frontal zone stretching from nrn GA to the SC coast. Associated ascent will support the continued sewd maintenance of a shield of enhanced precipitation through 06- 09Z, until a wave along the front moves toward the SC coast and causes the flow in that layer to veer, and brings an end to the preceding strong WAA. Aside from a shallow, ~500 ft deep above freezing layer near the surface, the 00Z GSO RAOB sampled a cold/sub-freezing and saturated column - one supportive of snow. As such, precipitation rates and associated "melting out" of the shallow above freezing layer will largely dictate p-type over the Advisory and Warning areas, as has been the case since this past afternoon when temperatures tended toward freezing (33-34 degrees) over the nw Piedmont, and more recently from the Triad to the Triangle during this more recent burst of snow. Temperatures are then likely to rise a degree or two once the precipitation intensity diminishes. The combination of both mid level warming related to the aforementioned strong 850 mb WAA, and a deeper above freezing surface layer south of the Advisory areas, characterized by surface temperatures in the upr 30s-40 degrees, will favor a cold rain there. The exception will be from RWI to IXA, where the rain will mix with or briefly change to snow and result in a coating on mainly elevated surfaces. Lift and associated deeper saturation through the mixed phase will diminish late tonight, so precipitation will likely end as a period of light rain and drizzle before tapering off Sun morning. && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... As of 425 PM Saturday... The by-now-shearing shortwave trough will be exiting to our SE Sun morning, with the primary surface low dissolving to a weak inverted trough over the S Appalachians and the secondary surface low moving further offshore. Copious low level moisture will remain, particularly over the W and S CWA, although the chilly wedging surface high may allow for some low level drying over the NE CWA. Nevertheless, expect a cloudy to mostly cloudy and cool day over much of the area, and we may see lingering drizzle over the Piedmont, especially west sections. Highs 43-50. Nocturnal cooling with the wedge holding firm Sun night will prompt the low clouds to hold firm, especially over the S and W. Lows 30-37. -GIH && .LONG TERM /MONDAY THROUGH SATURDAY/... As of 200 PM Saturday... Longer range forecast remains on track with much warmer weather returning by mid week. Cold air advection will continue Monday as high pressure ridges down the Atlantic coast. The cool ridge holds through Tuesday, though gradually weakening and lifting north into New England. The surface high lifting out combined with a mid level ridge axis over the area edging east and offshore Tuesday night will result in deep SW return flow with strong warm air advection setting up early Wednesday and continuing into Thursday. Temperatures on Wednesday will rise into the 60s and then soar into the 70s on Thursday. While all of this is going on locally, a long wave trof will be deepening over the Plains, with strong frontogenesis stretching out of the Gulf northeastward into the Ohio Valley during the mid week. The mid level ridge just east of the area will block and slow down the eastward progression of this surface front, allowing deeper layer moisture advection into the area, with precipitable waters edging above 1.5 inches prior to the front`s passage early Friday. A lot of favorable ingredients will be also be present which would support stronger shower and thunderstorm activity, which would most likely manifest as a line of strong convection immediately ahead of the front. Timing will be key, as just a little delay of frontal passage from Thursday night into Friday would add increased instability to the mix. Highs Friday will be in the mid 60s north to mid 70s south. Ridging builds in Friday night into Saturday with cooler and dry weather. Highs Saturday will range from 55 north to 65 south. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/...
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As of 140 AM Sunday... Widespread LIFR/IFR ceilings will persist through 10Z Sunday along with areas of rain across the south and rain/snow mixed across the north. the bulk of the precipitation will diminish/end by 10Z. Low overcast will persist through 15Z, then expect slow clearing, initiating in the northern coastal plain, reaching KRWI by mid day/early afternoon. This clearing trend will likely reach KRDU and KFAY between 17Z-20Z. Appears that ceilings will lift into the low end VFR by 19Z-21Z, though cloud cover may not totally depart. The potential exists for MVFR ceilings to occur later Sunday night, persisting into early Monday. VFR conditions expected across most of central NC. The exception will be the NW Piedmont/Triad terminals where lingering moisture will cause periods of MVFR ceilings Tuesday through Thursday.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 6 AM EDT Sunday for NCZ008>010- 025-026-038>041. Winter Storm Warning until 6 AM EDT Sunday for NCZ007-021>024. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...Hartfield LONG TERM...mlm/Franklin AVIATION...WSS is the U.S. government's official web portal to all federal, state and local government web resources and services.