Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 230752 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 355 AM 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. && .NEAR TERM /TODAY THROUGH FRIDAY NIGHT/... As of 315 AM Friday... 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. && .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/... As of 325 AM Friday... An improving weather pattern still appears in store for central NC early next week with temperatures closer to seasonal norms by mid week and beyond (finally!). A deep upper level low off of the Eastern U.S. seaboard will serve as a block to a digging l/w trough over the western U.S. In between will be an amplifying upper ridge, initially extending from the Deep South into the Great Lakes. This upper ridge progged to extend overhead by mid week. Subsidence associated with this feature should inhibit precip generation. Temperatures to start the work week will remain well below normal, generally in the upper 40s to lower 50s. Frosty mornings still expected Monday and Tuesday with min temps in the upper 20s to lower 30s. The moderating air mass will lead to afternoon temperatures by Wednesday closer to normal, solidly in the 60s to near 70 south, and mainly in the 70-75 degree range by Thursday. && .AVIATION /06Z FRIDAY THROUGH WEDNESDAY/... As of 115 AM Friday... 24 Hour TAF Period: VFR conditions will continue through the 24 hour TAF period as surface high pressure moves across the southeast U.S. Skies will be mostly clear/mostly sunny skies today, with mid/high clouds beginning to stream after 00Z from the northwest ahead of a mid level short wave. This wave will increase moisture advection into the west, with ceilings lowering progressively, although remaining VFR, through 12Z Saturday. Outlook: The approaching storm system will result in a trend to MVFR Saturday morning at INT/GSO/RDU, and Saturday afternoon at RWI/FAY. Meanwhile, precipitation will be spreading in from the NW, with ceilings at INT/GSO trending to IFR Saturday afternoon. The precipitation is expected to start off as a wintry mix in the morning, changing to all or mostly rain by mid day. IFR conditions will be widespread Saturday night, with a trend to MVFR Sunday, and further to VFR by Monday. VFR is expected for the remainder of the mid week. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...mlm NEAR TERM...mlm SHORT TERM...WSS LONG TERM...WSS AVIATION...mlm is the U.S. government's official web portal to all federal, state and local government web resources and services.