Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 172007 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 305 PM EST Sun Dec 17 2017 .SYNOPSIS... High pressure will settle east across the southeastern US through the weekend. A series of upper level disturbances will move through the region through mid week. && .NEAR TERM /THROUGH TONIGHT/... As of 1040 AM Sunday... Visible satellite and 12Z GSO upper air data suggest mid level clouds may have a greater impact than earlier forecast on high temperatures over the nwrn and nrn Piedmont, where highs may struggle to hit 50 degrees. Otherwise, filtered sunshine through considerable high cloudiness that will yield to thickening and lowering mid-high ceilings by this afternoon, should allow temperatures to range into the middle to upper 50s over the srn RAH counties. KFCX radar data indicates virga has already reached as low as 4 thousand ft AGL in the past hour over the Triad, so sprinkles or a slight chance of barely measurable rain is on track area-wide for the afternoon, especially across the nrn and nwrn Piedmont where glancing mid level forcing will be relatively maximized, and into the evening hours over the sern counties. Previous discussion as of 315 AM Sunday follows... Southern stream trough currently over the Oklahoma Panhandle will undergo significant de-amplification over the next 24 hours, shearing apart within the confluent flow as it tracks NE and east through the Ohio Valley during the afternoon and then off the Mid- Atlantic States late this evening, tracking along the western and northern periphery of the mid/upper level ridge in place across the SE US. While the better forcing/lift associated with the weakening trough will remain well north of the area, the associated low to mid-level moist plume, fed by a SWLY 50 kt mid-level jet, will spill east atop the mid/upper level ridge in place. This will result in thickening and lowering cloud ceilings during the afternoon and evening. There could be fairly widespread virga that may reach the ground in the form of patchy light rain or sprinkles by the late afternoon and through the evening/overnight hours. This moisture plume will quickly shift offshore shortly after 06z, with the potential for skies clear out late tonight, especially across the NW Piedmont. The thickening cloud cover could potentially temper afternoon highs, especially across the western Piedmont where earlier onset of thicker cloud cover would coincide with peak afternoon heating. Highs ranging from lower 50s NW to mid/upper 50s south. Lows tonight will be noticeably milder than previous nights, especially across the south, where clouds may linger. Lows ranging from mid/upper 30s NW to mid 40s SE. && .SHORT TERM /MONDAY AND MONDAY NIGHT/... As of 315 AM Sunday... As we await for the closed low over the SW US to eject eastward, the Carolinas will be in-between waves/systems on Monday, under the control of the flat subtropical high ridging north into the SE states. Deep westerly flow will result in a fair wx day with dry conditions along with a brief return of sunshine Afternoon temperatures will moderate into the 60s everywhere, under light southerly winds with the development of a surface trough in the lee of the mountains. Mild overnight lows in the 40s. && .LONG TERM /TUESDAY THROUGH SUNDAY/...
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As of 305 PM Sunday... Frontal zone south of the area will be lifted north as a strong mid level wave over the southwest US ejects eastward across the southern plains on Tuesday. High cloudiness will be prevalent with an initially dry and mild airmass in place over the area benefitting from zonal flow to allow highs to reach the mid 60s. A moisture plume off the western Gulf will be aimed east along the frontal bounday, which will be in the vicinity of the NC/SC border, producing increased cloudiness rapidly ahead of the mid level system Tuesday night. Expect to see light rain spreading into the western Piedmont by Wednesday morning and across the remainder of the area Wednesday into Wednesday night. PoPs will peak on Wednesday, graduated from 40% north to 70% across the south, and may wind up being bumped considerably higher if we see see continued model consensus on the timing and precip distribution. Mins Tuesday night will be mild, mostly mid and upper 40s, with highs on Wednesday in the mid and upper 50s. The upper wave and associated cold front will move offshore Wednesday night, with drier but only modestly cooler air ridging down the Atlantic seaboard from the northeast. High temperatures will take a short-lived tumble to near seasonable levels as the CAD builds in, topping out mostly in the lower 50s Thursday. The surface high associated with the CAD will be progressive, allowing the airmass to begin scouring out Thursday night as low level veers easterly, with highs edging back to the mid and upper 50s Friday ahead of our next cold front, which will move into the area and stall over the weekend. Seasonable temperatures in the 50s are expected Saturday and Sunday, with at least chance (30%) PoPs through the weekend.
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&& .AVIATION /18Z SUNDAY THROUGH FRIDAY/... As of 1255 PM Sunday... A mid level trough and associated mid-high level moist axis will lift rapidly enewd across the srn-cntl Appalachians (and NC) through this evening, with an associated thickening and lowering of ceilings down to between 5 and 10 thousand ft for a several hour period late this afternoon and this evening. While most associated precipitation will evaporate before reaching the ground (virga), some light VFR rain or sprinkles will be possible from west to east between 20Z and 03Z Mon. Skies will also generally clear from west to east thereafter/early tonight, although an area of lower level clouds -- in the low VFR to high VFR range-- are expected to expand/develop enewd across SC and srn NC later tonight through early Mon. This cloud area may result in a short period of MVFR ceilings around 2500- 3000 ft at KFAY in the several hours centered around 12Z Mon. Outlook: The nwd retreat of a warm front, and leading edge of a more humid air mass, will result in a medium chance of advection fog, and/or VLIFR stratus, Mon night-Tue morning, particularly at FAY. There will then be a high chance of rain and sub-VFR conditions, heaviest and lowest at FAY, late Tue night through Wed night, with the passage of a low pressure system across the sern U.S. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...CBL NEAR TERM...MWS/CBL SHORT TERM...CBL LONG TERM...mlm AVIATION...MWS

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