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Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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663 FXUS62 KRAH 171803 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 203 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 300 AM Saturday... There is a slight risk (level 2 of 5) for areas from Raleigh south and east to the Coast Sunday afternoon and evening. There is a marginal risk (level 1 of 5) for areas to the north and west of Raleigh including the Triad Area. The mid/upper level trough will through the Mountains on Sunday afternoon and evening. A pre-frontal trough should be in place over the Piedmont with the actual cold front trailing back over the mountains. Surface heating of the very moist air mass over the region will likely lead to moderate instability by afternoon over the eastern Piedmont eastward. MLCape of 2000 to 2500 J/kg is expected in the east, with 1500 to 2000 in the west depending on cloud cover. Thunderstorms are expected to develop by early afternoon with CAMS now suggesting the likely stronger storms (a few possibly severe) in the areas of the eastern Piedmont to the Coastal Plain. Some stronger storms will also be possible with the actual cold front in the west during the evening. Convection should diminish during the late evening with some potential for activity along the cold front into the overnight hours of weaker intensity. Locally heavy rain is expected, especially in the east. However, widespread flooding is not expected. Highs should range in the mid 80s NW to lower 90s SE. Lows in the mid 60s north to lower 70s SE. && .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...Badgett LONG TERM...Swiggett AVIATION...Green