Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 231802 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 200 PM EDT Fri Mar 23 2018 .SYNOPSIS... Cold high pressure will extend across the region today, then move offshore late tonight. An area of low pressure will approach from the west Saturday and cross our region Saturday night and Sunday bringing unsettled weather and the chance for some winter precipitation across northern portions of the forecast area. Chilly high pressure will build southward into the Carolinas Sunday and Monday. && .NEAR TERM /THROUGH TONIGHT/... As of 1023 AM Friday... Very minimal change to the forecast this morning but otherwise a quiet day across central NC with temperatures in the mid 50s to near 60 degree as high pressure lingers southwest of the area. This will keep northwesterly flow overhead with some gusts to 15 mph this afternoon. Previous discussion follows. -Ellis Mid level ridge axis has shifted offshore, with surface high pressure over the western Great Lakes edging in to maintain cool air advection today, suppressing high temperatures despite strong sunshine. Pressure gradient relaxes during the afternoon, with lighter northwest winds than past couple of days, 10-12 mph gusting to 20 mph. Will thus be a little more pleasant given highs edging up slightly to mostly mid 50s north, with potentially some low 60s in the southern counties. Initially clear skies with a cool airmass in place will allow for decoupling early tonight and mins will fall to the mid 30s across the north towards midnight, with temps bottoming out within a degree or two of freezing across the northern tier by morning to mostly mid 30s across the south. Concurrently, a low pressure area will be migrating east across the Plains, which will back the low level flow and gradually increase moisture advection into the southwest Appalachians after midnight. Precipitation will gradually spread eastward as the isentropic lift strengthens and the airmass saturates, but it appears that appreciable chances for rain or a mix of rain/snow will hold off until after sunrise Saturday morning. -MLM && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 350 AM Friday... Still dealing with a complex weather pattern for the weekend, with a wintry mix likely across the northern half of central NC Saturday night into the very early Sunday morning. A s/w in the nw flow aloft will dive sewd from the Upper Midwest into the lower OH Valley Saturday. This system will encounter increasing confluence aloft, so it should weaken with time. The system will induce isentropic upglide across central NC Saturday as a sfc warm front should lie to our south and a weak ridge of high pressure lies overhead. There will likely be radar return early Saturday morning when sfc temperatures are close to or just above freezing in the Triad. However, most of the precipitation aloft will likely evaporate as the sub cloud layer will remain quite dry through mid morning. Thus, any snowflakes that reach the sfc will melt on impact. The bulk of the precip Saturday will be in the form of rain, overspreading central NC from the nw. With precipitation onset expected to occur during the morning into the mid day hours, temperatures will struggle to warm during the day. Thus have lowered max temps Saturday, especially across the east and south from the previous forecast. The wintry mix will likely be first encountered across the far northern counties in vicinity of the Virginia border late Saturday- Saturday evening as precip rates increase. GFS sounding data suggest a fairly deep isothermal layer extending from 950-700mb. This suggest mostly snow during times of high precip rates, and rain/snow during times of lighter rates. Currently appears the highest precip rates will occur late Saturday evening into the first half of the overnight. This places the greatest risk for accumulating snow across the Virginia border counties and possibly the far northern coastal plain. Expect impacts to be minimal or low as a good deal of rain prior to wintry onset will warm/insulate the ground and sfc temperatures expected to remain above freezing during most of the episode. At worse, expect snow accumulation to be limited to grassy areas and on the tops of decks, roofs, cars, etc., and no worse than a slight slush build up on a few roads. Precip rates expected to wane during the last half of the overnight through early Sunday morning, and the atmosphere projected to dry out in the favored dendrite growth area. This should lead to a mixture of rain/sleet/snow, with a brief instance of freezing rain probable as sfc temps get to or drop briefly below freezing at daybreak. Any icing that occurs will be very spotty and light with no travel problems expected. Do not plan to issue an advisory with this package, though if the models remain consistent, an advisory will likely be needed for portions of the northern Piedmont and northern coastal plain. Precipitation will end north to south Sunday morning as the wave exits our region. Drier air will infiltrate the atmosphere, leading to spotty light precip in the morning, and partial clearing Sunday afternoon. && .LONG TERM /MONDAY THROUGH FRIDAY/...
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As of 200 PM Friday... Dry and cool weather is expected during the first part of the work week. A few low clouds may hang on through Mon morning in the western CWA as the semi-anchored surface high, centered over SW Quebec into the Maritimes, ridges SSW through NC, generating a weak wedge air mass over central NC. Nocturnal stabilization and a local increase in shallow moist upglide may result in patchy drizzle over the W Piedmont Mon night. Mid level ridging will steadily build over the East Coast through mid week, between deep closed lows over the Desert Southwest and over the NW Atlantic, ensuring a lack of forcing for ascent and continued tranquil weather (albeit with periodic cloudiness, particularly with SW-to-NE passage of a warm frontal zone aloft through the region). The GFS/ECMWF weaken the Desert Southwest low and track it eastward into the Southern Plains by Thu, which nudges the ridge axis offshore and leads to increasing moist SW flow into the area, prompting a rising chance for showers late in the week. This is supported by the GEFS and EPS, although both the ECMWF and EPS lag a bit, closer to the slow Canadian solution. Will opt for the ECMWF`s compromise but slower solution, introducing low shower chances Thu with slightly better chances Fri, but still just near climatology. Surface temps will continue to modify through the week, with soaring 850 mb temps, supporting a trend of highs from the upper 40s to upper 50s Mon to the upper 60s to mid 70s by Fri. -GIH
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&& .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... As of 1140 AM Friday... VFR conditions will hold through tonight, with gradual deterioration thereafter. An upper level trough just off the Eastern Seaboard today will continue shifting eastward through tonight, while a surface high centered over E Canada and extending southward through NC weakens as a frontal zone approaches from the SW. Little more than scattered high-based flat cu are expected through late afternoon. An upper level disturbance moving in from the WNW will bring increasing clouds starting this evening, and rising chances for precipitation, starting near daybreak at INT/GSO and slowly spreading to RDU and then FAY/RWI toward the end of the TAF valid period. High and mid clouds will overspread the state from the west this evening through tonight, with lowering bases, although it will remain VFR at all central NC terminals through 12z Sat. INT/GSO will trend to MVFR 12z-15z, followed by RDU 15z-18z. INT/GSO will see a chance for rain or snow after 15z Sat. Looking beyond 18z Sat: The trend down to MVFR will spread to eastern terminals after 18z, while western terminals trend to IFR. A band of mostly light precip, rain mixed with a little wet snow, will overspread northern terminals Sat afternoon, with a lower chance at FAY. Starting late Sat afternoon, all locations will become IFR/LIFR with a solid area of heavier precip, mostly rain with a little sleet at FAY and a wintry mix or mainly snow/sleet at INT/GSO/RDU/RWI. This will continue through Sat night into early Sun morning. Dry weather is expected after 15z Sun, but cigs should remain IFR into Sun evening. RDU/RWI/FAY should trend to MVFR Sun night, while fog/stratus may redevelop at INT/GSO overnight, with a potential pre- and post-dawn period of IFR conditions. All locations should become low-end VFR by Mon afternoon, and VFR conditions will then dominate through Wed as deep high pressure settles over and just offshore of the Carolinas. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Ellis NEAR TERM...Ellis/mlm SHORT TERM...WSS LONG TERM...Hartfield AVIATION...Hartfield is the U.S. government's official web portal to all federal, state and local government web resources and services.