Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 191945 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 345 PM EDT Mon Mar 19 2018 .SYNOPSIS... A warm front will lift north into the area this evening, where it will then stall tonight. There will be a series of low pressure systems developing along the front as it pushes slowly south of the Carolinas through early Wednesday. && .NEAR TERM /THROUGH TUESDAY/... As of 300 PM Monday... High pressure edging further offshore and thinning clouds allowed highs to rise well into the 60s, which further weakened the isentropic gradient which resulted in anemic patches of light rain or virga into the afternoon. Expect the cloudiness to become widespread and lower quickly as we lose sun and low level flow strengthens atop a surface warm front lifting north into the area where it will creep slowly north to the I64 vicinity by late tonight. Isentropic lift will be on the increase progressively tonight as well, and will raise the PoPs to near 100 percent, progressing from southwest to the east by morning as a surface wave moves east across the southern tier. Rainfall amounts should range from a minimum of at least a half inch to perhaps 1.25 inches across the northern tier where frontal zone enhances rain rates. Most unstable CAPE across the southern tier reaches 300-400 Joules, with increasing low level shear south of the frontal zone, so will include a chance for thunder across the southern couple of tiers of counties. Lows will be mild, from the mid 40s north of the front to mid or even upper 50s across the south. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 345 PM Monday... A compact shortwave trough/low over the mid MS Valley will migrate ewd, to the lwr OH Valley by 12Z Tue - slower and more amplified than indicated in previous forecasts. This solution will allow a pair of upstream/trailing srn stream perturbation (elongated mostly shear vorticity axes) over the Four Corners and Front Range of the cntl Rockies to amplify across the lwr MS and TN Valleys, and ultimately be "captured" by the the aforementioned closed low over the OH Valley, as it drifts across the Virginias Tue night-early Wed. Associated 120-150 m mid level height falls, and strong QG- forcing for ascent, will pivot from the srn Appalachians at 00Z Wed to the NC coast by 12Z Wed. At the surface, a nearly stationary front will be draped in the vicinity of Highway 64 at 12Z Tue, with a lead frontal wave over e- cntl NC, and a trailing one poised to develop over nrn SC as the aforementioned strong mid-upper level forcing pivots east of the srn Appalachians. A cooler and stable air mass will exist north of the front, where the heaviest rain will have likely occurred tonight, while a warmer and slightly unstable airmass will reside south of the front, or develop with diurnal heating with a few breaks in the multi-layer clouds over srn and sern NC. That trailing/secondary low, is then forecast to deepen as it wraps up the middle Atlantic coast through Wed, with associated cooler post-frontal plunging swd across cntl NC Tue night-early Wed. Widespread stratiform rain over the nrn Piedmont will decrease in intensity through midday, though with continued periods of light rain or drizzle from a low ovc Tue, while a band of convection will likely develop along the advancing front through srn NC through early-mid afternoon. The combination of (albeit weak) instability and strong shear profiles suggest a few storms could become strong to severe from near Maxton to Fayetteville to Goldsboro and points sewd, and offshore through Tue evening. At the same time, a mid level deformation band will be developing over the srn Appalachians and TN Valley, then pivot newd across cntl NC, coincident with the maximum of mid level height falls referenced above, Tue night-early Wed. Similar to the last event, partial thicknesses/deep layer thermodynamic profiles will trend sufficiently cold for snow aloft, with the primary inhibiting factor being a slightly above freezing boundary layer. With that in mind, and also similar to the last event, melting of snow and associated cooling of the boundary layer to (near) freezing would likely occur when the heavier precipitation rates occur, and/or when insolation will be at a minimum during the early morning hours Wed. A light, slushy accumulation will accordingly be possible mainly north and west of an arc from EXX to RDU to ETC, where our "most likely" accumulation includes a Trace to up to one half or three quarters of an inch. Any accumulation will be short-lived and limited to when the precipitation rate exceeds the melting rate at the surface, with a change over to rain by midday, as surface temperatures rebound into the upr 30s-lwr 40s. The precipitation may end as flurries or light snow over the ne Piedmont and nrn Coastal Plain before ending Wed evening. While there will be some threat of black ice Wed night, as temperatures dip into the lwr to mid 30s, no widespread travel problems are anticipated. && .LONG TERM /THURSDAY THROUGH MONDAY/... As of 300 PM Monday... The surface low will be lifting rapidly northeast with dry and cooler high pressure building into the area on Thursday through Friday. Temperatures will be cool, from upper 40s north to mid 50s south on Thursday, and a couple of degrees warmer on Friday. Lows Friday morning will fall below freezing over most of the area, with northern tier counties perhaps falling into the upper 20s. Northwest flow into the weekend will provide increased cloud coverage and some light rain into the west to tighten up our damming signature and produce highs ranging from the low 50s north to low 60s south. Return flow will increase rain coverage on Sunday, further strengthening the ridging, with highs in the 50s to lower 60s Sunday and Monday. && .AVIATION /18Z MONDAY THROUGH SUNDAY/... As of 140 PM Monday... 24-Hour TAF Period: Initial VFR conditions this afternoon will linger through 00Z. Southerly surface flow will strengthen ahead of a low pressure area moving across the southern tier of the state tonight. Increased moisture and upglide will induce ceilings to lower quickly through MVFR to IFR from 00-06Z, with light rain blossoming and becoming widespread through the period. IFR/LIFR ceilings are expected after 06Z, to linger past 12Z with marginal improvement to MVFR towards 15Z. Looking ahead: Passage of a series of low pressure systems will result in sub-VFR conditions and periods of rain, probably mixed with or briefly changing to snow at the northern TAF sites late Tuesday night into Wednesday. Drying and a return to VFR conditions from west to east will occur as the final trailing low lifts away from the middle Atlantic coast Wednesday night. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...CBL NEAR TERM...mlm SHORT TERM...MWS LONG TERM...mlm AVIATION...mlm is the U.S. government's official web portal to all federal, state and local government web resources and services.