Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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853 FXUS62 KRAH 171739 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1240 PM EST Sat Feb 17 2018 .SYNOPSIS... A warm front will gradually lift north into the southern counties of central NC this afternoon then stall. A weak cold front will approach from the west later today and cross our region tonight. High pressure will build into the area Sunday, then quickly drift offshore Sunday night. && .NEAR TERM /THROUGH TONIGHT/... As of 1055 AM Saturday... Just minor tweaks required to the near term forecast, primarily to adjust PoPs down a touch through early afternoon. Low level cold air advection and overcast skies preventing temperatures from rebounding this morning. Most locations have seen temperatures hold steady or fall a degree or two since sunrise. Expect this trend to continue through the afternoon. Per SPC meso- analysis, 850mb flow beginning to increase to our south-southwest. This strengthening isentropic upglide should cause patchy light rain to develop across the southern and western Piedmont through 3 PM, and over the remainder of central NC late this afternoon-early this evening. Should see an increase in coverage toward dusk-early evening as a mid-upper level s/w gets closer to central NC. Still expect overall rainfall totals to be light, with most locations totaling less than a quarter of an inch. The overcast skies, continued low level cold air advection, and patches of light rain will cause temperatures to show very little variation from current levels through this afternoon. Tonight, the mid-upper level s/w will traverse across the region this evening, accompanied by patchy or areas of light rain/drizzle. The bulk of this precip should be diminishing or ending shortly after midnight. NW flow behind the exiting s/w will advect a drier air mass into central NC, possibly leading to partial clearing across the Piedmont very late tonight. Whether the clouds depart by morning will play a role in the minimum temperature forecast across the Piedmont. Current low temp forecast based on partial clearing to occur, allowing temperatures to drop into the mid-upper 30s. If clouds hold on through daybreak, min temps at or slightly above 40 degrees will be more probable. && .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... As of 345 AM Saturday... As continental high pressure moves in on Sunday, expect rain to stop and skies to clear. This will be a fast moving transitory high that will end up moving east of the area and offshore by Sunday night. For all the chilly temperatures on Saturday, Sunday will feature highs in the upper 50s to middle 60s across the area. Winds will begin to swing around to southerly by Sunday evening setting up the beginning of return flow that will exist early next week. Sunday night lows in the 40s with highest temps in the southwest. && .LONG TERM /MONDAY THROUGH FRIDAY/... As of 330 AM Saturday... A very warm work week is likely, with the potential to set some more record highs midweek. Mon/Mon ngt: We`re likely to see some like overrunning rain, particularly over the NW CWA, associated with the northward passage of an elevated warm front through the area. As the surface high moves off the coast, a surface warm front, located south of the area early in the day, will progress northwestward into the CWA, although the NW half should hold onto the cooler stable air through Mon night. Skies should be generally cloudy, with highs from the upper 50s NW to the lower to mid 70s SE as thicknesses there soar well above normal. Expect lows in the low-mid 50s NW (likely occurring early in the night, with temps steady or rising late) to the upper 50s/near 60 SE. Tue/Tue ngt: There is a good chance that the Triad area (especially INT) will still be within the in situ stable pool at daybreak Tue. But the building and deepening ridge over and just off the SE coast (highlighted by a mid level anticyclone off the Savannah GA coast that expands toward NC during the day) and subsequent subsidence aloft should allow for enough insolation atop this vulnerable stable layer to prompt its eventual erosion Tue. Still anticipate muted warming over the NW, however, as the low levels will remain moist. Should see low stratus and fog to start the day, breaking up outside of the NW sections with heating. Highs from the upper 60s NW to near 80 SE, where thicknesses may reach 60-70 m above normal, and records may be threatened (see climate section below). Mild lows of 57-62, with a potential round of nighttime stratus over the Piedmont. Wed-Fri: Wed will be another very warm day, but the mid level flow will begin to flatten a bit, transitioning from anticyclonic to neutral from the SW, allowing subtle perturbations emanating from the weak low located off Baja California this morning to track toward the region. As low level moisture inflow strengthens off the Gulf, clouds and precip chances will increase, primarily over the NW CWA Wed/Thu as a surface cold front (along the periphery of the Southeast ridge) approaches from the W and NW. Forecast uncertainty increases considerably starting Thu, as models differ as to whether or not this front pushes into NC as a backdoor front, and if so, how far south it goes. This all depends upon the amplitude of a wave passing through the St. Lawrence Valley and New England as well as on the density of the surface high behind the front, both factors with low predictability at this time range. Given this, will be more conservative but lean toward a warmer solution, as the ECMWF has been trending toward a stronger mid level ridge over the Southeast late week. Will go with just chance pops for now near and south of the approaching front Thu/Fri, but confidence in the details is low. Highs in the 70s to lower 80s Wed, upper 60s to upper 70s Thu, and lower 60s to lower 70s Fri, with a front potentially near or into northern sections of NC these latter two days, with mostly cloudy skies. -GIH && .AVIATION /18Z SATURDAY THROUGH THURSDAY/...
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As of 1240 PM Saturday... Aviation parameters will gradually deteriorate across central NC through the afternoon as ceilings will lower into the IFR/low end MVFR range while areas of light rain and/or drizzle develop, reducing the visibility into the IFR category. These adverse aviation conditions will persist through the evening. A weak sfc cold front will traverse the region overnight. Nwly winds will usher in a drier air mass, leading to lifting/dissipating ceilings and an end to the spotty light precip. There may be a brief period of IFR/LIFR visibility due to fog between 09-13Z Sunday in proximity of the Triad terminals and possibly KRDU, but forecast confidence is not high enough at this time to mention in the terminal forecast. VFR parameters expected Sunday but this will not last much into Sunday night as another low pressure system will begin to effect our area, leading to MVFR/IFR ceilings and areas of light rain late Sunday night through Monday. While an improvement in aviation conditions expected Tuesday through Thursday with periods of VFR parameters, a moderately moist atmosphere will lead to the probability of sub VFR parameters, primarily during the late night-early morning hours due to low clouds and patchy fog.
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&& .CLIMATE... RDU Records: Date | High Year | High Min Year ------------------------------------------ 02/20 75 1939 62 1939 02/21 76 2011 55 1939 GSO Records: Date | High Year | High Min Year ------------------------------------------ 02/20 74 1922 56 1939 02/21 74 2011 50 1954 FAY Records: Date | High Year | High Min Year ------------------------------------------- 02/20 82 2014 60 1939 02/21 80 1991 61 1953 && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...Ellis LONG TERM...Hartfield AVIATION...WSS CLIMATE...KC/Badgett

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