Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 200659 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 300 AM EDT Tue Mar 20 2018 .SYNOPSIS... A warm front will lift northward tonight into southeastern NC. Low pressure will track NE along the front late tonight and Tuesday. This will push a cold front offshore late Tuesday. This will be followed by a cold upper level low pressure that will track east across the area Wednesday. && .NEAR TERM /THROUGH TONIGHT/... As of 1050 PM Monday... Little change required to the near term forecast. Rain showers will increase in coverage through 07Z in advance of a mid level s/w and attendant sfc low. 00Z upper air analysis depict strong mid-upper level jet crossing the TN Valley/Deep South, placing central NC in a zone of decent speed convergence. With the lift increasing into the overnight, should see scattered-numerous showers develop/move across the region. Thus, plan to maintain the categorical PoPs overnight. Instability still lacking across the region and appears the better instability will remain well to our south. Mid level lapse rates marginal at best. So while a clap or two of thunder cannot be ruled out, the better chance for thunderstorms expected to remain south of our region across GA and SC. Overall threat for severe storms appears minimal, except in immediate proximity to the SC border where a marginal threat for a strong wind gusts/nickel size hail may exists in the 3 AM-7 AM time frame. Min temps by early Tuesday should vary from the mid 40s near the VA border to the mid 50s near the SC border. && .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 /WEDNESDAY NIGHT THROUGH MONDAY/...
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As of 300 AM Tuesday... Wed night: The upper low will shift off the Delmarva and NJ coast, but a last shot of energy diving into the departing trough combined with lingering moisture at 1-3 km AGL (evident in 700 mb progs) may bring a final sprinkle or flurry across the N and NE Wed evening, but with waning lift, expect little to no additional significant precip after nightfall. Skies will trend to fair overnight, responding to rebounding heights, with just high cloudiness late as sheared trailing vorticity streaks SE over the Carolinas. Lows in the low-mid 30s. Thu through Sat: Expect mostly sunny/mostly clear skies, along with much below normal temps as a seasonably chilly high builds in from the NW/N. We may see a few shallow showers Fri with moistening in the upper reaches of a deep mixed layer as a weak mid level wave dives SE over the Southeast states. And passage of a warm frontal zone aloft SW to NE into the region will bring a few more clouds and perhaps another shower risk on Sat, mainly over the SW CWA. Highs in the 50s to around 60. Lows in the 30s. Sun/Mon: Model differences grow. The ECMWF amplifies ridging over Eastern NOAM between Rockies troughing and a deep low over the NW Atlantic, while the GFS (and to a lesser degree the Canadian) drop energy down the back side of the NW Atlantic low, causing notable height falls down the Northeast and Mid Atlantic and yielding a much more west-positioned low. This latter solution generates wintry precip over NC, mainly N/E sections, while the former (ECMWF) has all liquid precip chances mainly over the W/S. With confidence low, will lean toward climo, with only slightly below normal temps and a near-climo chance for rain. -GIH
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&& .AVIATION /06Z TUESDAY THROUGH SATURDAY/... As of 155 AM Tuesday... Aviation conditions will deteriorate overnight as an area of rain and a few embedded storms crosses central NC. Cigs are already MVFR at INT/GSO/RDU, and will become MVFR at RWI/FAY in the next couple of hours as the rain and isolated storms overspreads the area. All locations will trend to mainly IFR during the predawn hours, after 08z. Behind this precipitation, a return to MVFR is expected at INT/GSO/RDU by 14z, but these locations should stay MVFR through Tue within a residual cool stable pool. At RWI/FAY, however, a trend to VFR is expected by 16z. Much of central NC should be mostly dry from 14z until late today, around 22z. After this time, rain chances will start to rise once again from SW to NE, and cigs at all sites should trend back down to MVFR or IFR. Winds will be mostly under 10 kts, light/variable or from the SE or S this morning before veering to mostly N then NE during the day. Looking beyond 06z Wed, IFR conditions are likely (mainly cigs) the rest of tonight through daybreak Wed, with widespread rain. Rain will taper down to patchy light rain (or a brief rain/snow mix at INT/GSO/RDU/RWI) Wed morning before ending gradually W to E during the afternoon with a trend to MVFR or VFR. Behind this storm system, VFR conditions are expected late Wed night through Fri, although a few showers are possible Fri and again Sat as a warm front approaches the area from the SW. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Badgett NEAR TERM...WSS SHORT TERM...MWS 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.