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Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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002 FXUS62 KRAH 171831 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 230 PM EDT Sat Aug 17 2024 .SYNOPSIS... A surface cold front and deep upper level trough will approach our area from the west tonight through Sunday, then move through the region late Sunday through Monday. && .NEAR TERM /TODAY THROUGH TONIGHT/... As of 835 AM Saturday... Some scattered showers have developed around the Charlotte metro area a little earlier than expected. Updated the pops across western counties to account for the showers this morning, plus tweaked pops northeast of Raleigh to account for a few small showers there. Have not made any changes to the afternoon forecast at this time. Previous discussion follows. As of 225 AM Saturday... A chance of mainly PM showers and thunderstorms in the west and central areas (Piedmont) today. An MCV associated with previous showers and thunderstorms over the NW and W part of the Piedmont was still evident in the satellite data tracking east across VA/NC. There continued to be mid and high level cloudiness in all but the Coastal Area. Isolated showers continued over central VA early this morning. CAMS suggest that isolated to widely scattered showers are possible this morning, mainly from the Triangle area north and east. However, it appears it will be this afternoon and evening when the best chance (30-40 percent) appears in the Piedmont. The chances taper to slight chances in the Coastal Plain this afternoon and evening. While an isolated strong storms is possible, mainly over the Triad and northern Piedmont this afternoon and early evening, the marginal risk remained just to our NW. Highs will top out mainly between 85- 90. The chance of showers/storms occurs as the mid/upper level trough to our NW approaches the mountains later today. A weak lee pre-frontal trough is expected over the Piedmont this afternoon and evening. Isolated showers/storms will be possible tonight. Otherwise, most of the convection will end by late evening. Lows in the lower 70s. && .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... As of 230 PM Thursday... ...There is a slight risk (level 2 of 5) for severe storms from Raleigh south and east Sunday afternoon and evening... ...There is also a risk for Isolated Pocket of Heavy Rain and Flash flooding along and east of US 1... An unseasonably strong()~3 S.D. below normal) and amplifying upper- level trough will dig SEWD into the Eastern US Sunday during the period. At the surface, a pre-frontal sfc trough in the lee of the Appalachians will get overtaken by the accompanying cold front that will move east across central NC during the late afternoon and through the overnight hours. As daytime heating commences, moderate destabilization is expected area-wide, maximized across the Sandhills and southern coastal plain. Coincident with the arrival of the cold front and core of the stronger 40-50 meter H5 falls into the area, showers and storms are expected to develop across the western Piedmont between 18-21z, with convection thereafter increasing in coverage and intensity(becoming better organized) as the progresses eastward into the central Piedmont and western Sandhills between 20-00z, and then across eastern Sandhills and coastal plain counties between 23-04z. Deep layer shear of 30-35 kts will likely favor multi-cellular severe threat, with damaging winds the primary threat. Given recent wetness and with area streams and creeks still running high, the convective downpours could also lead to some instances of flash flooding, especially in poor-drainage and urban areas. The severe threat appears greatest between 3 to 10 pm with generally dry conditions after midnight. Highs ranging from mid 80s north to lower 90s south. Lows in the mid/upper 60s to lower 70s south. && .LONG TERM /MONDAY THROUGH SATURDAY/... As of 200 PM Saturday... Sat/Sat night: A mid/upper level trough will be positioned over the eastern CONUS with the trough axis extending from southern Quebec trough the Mid-Atlantic and into FL. A leading effective front from prior convection is expected to be situated near the coast with lee- troughing extending through the Piedmont. Surface dew points within and east of the lee-trough should still be in the mid 60s to near 70 and result in 500-1500 J/kg of MLCAPE through daytime heating. A disturbance rotating through the backside of the trough will overlap this weakly unstable airmass and a reinforcing cold front pivoting across central NC to initiate scattered showers/storms during the afternoon/evening hours. The best overlap of synoptic forcing and available instability will be over Northeast Piedmont into the northern/central Coastal Plain. Mid-level flow in the core of the trough will be relatively weak, but some directional shear (20-30kts of 0-6km shear) may lead to some storm organization in this region where clusters organized along a common cold pool will be most probable. DCAPE and theta-e differences will be lower than previous days (around 600 J/kg and 20K, respectively) and lead to a marginal/conditional threat for severe wind gusts. Tues through Sat: The passage of a reinforcing front will mark a pattern change with dropping low-level thicknesses through Tues. High pressure will then shift over the Northeast and ridge down through the Mid-Atlantic through much of the work week. Highs in the upper 70s to mid 80s will become common each afternoon with dew points in the 50s to near 60. Overnight, pockets of calm conditions and clear skies will favor radiational cooling Tues night into Fri morning with lows falling into the mid/upper 50s to near 60. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... As of 130 PM Saturday... TAF period: There is a TEMPO group in the FAY TAF for some passing showers at the beginning of the period. However, with less than a 30% chance of a shower/storm at any of the TAF sites during the forecast period, did not mention precipitation in any of the TAFs, although a shower/storm cannot be ruled out anywhere. The most likely possibilities would likely be at INT/GSO in the late afternoon or FAY after dark (as an area of precipitation may move just to the west). As for late night restrictions, have gone with persistence at INT/GSO where both sites developed low ceilings. Considering how much the dewpoint has risen at RDU as of early afternoon, also added a mention of LIFR ceilings to match INT/GSO`s observations from this morning. There is enough confidence in lower ceilings at FAY/RDU to go with prevailing ceilings, right around 1000 ft. Outlook: Scattered showers/storms are expected at INT/GSO Sunday afternoon, with prevailing shower/storms at the other 3 sites. A chance of precipitation will linger at all sites on Monday, but the rest of the outlook period should be dry. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Badgett/Hartfield NEAR TERM...Green/Badgett SHORT TERM...CBL LONG TERM...Swiggett AVIATION...Green