Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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367 FXUS62 KRAH 220734 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 335 AM EDT Sun Sep 22 2024 .SYNOPSIS... A back-door cool front will drop south into the area this afternoon and evening and tonight. The front is expected to become quasi- stationary INVOF of upstate SC and southern NC, eventually washing out early week as weak high pressure extends south down the mid- Atlantic coast. && .NEAR TERM /TODAY AND TONIGHT/... As of 330 AM Sunday... Central NC will remain in the NW flow between the upper ridge centered over the western GOM and lower MS Valley and upper trough moving east out into the western Atlantic. A back-door cool front is forecast to work it`s way south through the area during afternoon and evening. Upper impulse and associated convective cluster will exit SE of the area over the next few hours. In it`s wake, some patchy fog and low clouds/stratus may develop around or shortly after daybreak, especially across the northern/central coastal plain and possibly extending into the eastern Piedmont counties as a back-door cool front sags in from the NE. These low clouds could linger/hold on over NE portions for a fairly substantial portion of the diurnal heating cycle, which will likely set-up an impressive NE to SW temperature gradient across the area, while also making for a challenging max Temp forecast today, especially along it`s eventual western fringes. HREF probabilistic guidance indicates as much as 8 degree spread in afternoon temps, with the greatest uncertainty centered over the central Piedmont, including the Triangle. Highs ranging from mid/upper 70s northern coastal plain, lower/mid 80s interior sections, and upper 80s/near 90 across the southern Piedmont. Isolated showers/storms will be possible as the front slips southeast, mainly across eastern/coastal plain sections where the best instability is forecast. Widespread low clouds/stratus will spread NE to SW during the the evening and overnight hours. Additionally, some showers could spread into the western/NW Piedmont tonight as shortwave impulses spread in from the west within a mid- level plume of enhanced moisture and WAA. Lows ranging from lower 60s NE to upper 60s southwest. && .SHORT TERM /MONDAY AND MONDAY NIGHT/... As of 330 AM Sunday... Weak H5 rises are expected over the region on Monday as the upper ridge over the GOM builds towards the Florida Peninsula. The aforementioned back-door cool front near the SC/NC border early Monday could retreat back north during they day. Meanwhile, downstream of the an upper shortwave trough over the Mid/Lower MO Valley, weak disturbances will continue to eject east atop the mid- level ridge axis and through the region, keeping a plume of enhanced mid-level moist and WAA focused over NC and VA, with PWATS forecast to increase to ~2.0" by Monday evening. We`ll see considerable multi-layer cloudiness across central NC, especially the western Piedmont. Weak to moderate destablization across the southern and western Piedmont will support a chance of showers and storms, especially during the afternoon and evening, with general model consensus the potential for scattered shower/convection to spread east into central and eastern NC Monday night. Highs Monday ranging from mid/upper 70s north to mid 80s south. Lows again in the lower 60s NE to upper 60s south. && .LONG TERM /MONDAY THROUGH SATURDAY/... As of 230 PM Saturday... * Near to slightly above normal temperatures into midweek, followed by seasonal to slightly below average late week and weekend * Shower and storm chances highest Tue into Thu * Forecast confidence decreases mid to late week as ensemble systems continue to differ on the overall synoptic pattern and possible tropical influences We will start the week with ridging building into the area at mid- levels from the north and northeastern Gulf. High pressure will build into the area from the Eastern Seaboard and Canada. Models still show a lingering backdoor front to our southwest in northern SC, though it appears models have trended further south with its location. As such, rain/storm chances are lessened Mon aftn/eve, but still cannot rule out a 20-30 percent chance over the western and southern Piedmont. Temperatures will be near normal in upper 70s to low 80s. Ridging will continue into midweek, though we should get increasing influence from a trough over the MS/OH valleys and Great Lakes late Tue through early Thu. Model and ensemble solutions start to diverge on how the trough evolves as it moves east, but there does appear to be a general consensus that a cold front will try to move through sometime Thu morning. It`s still unclear whether it will actually move through or stall out and linger NW of us. Ahead of that front, shower and storm chances should increase (30-60 percent), primarily in the late Tue through Wed night period. Temperatures should rise above normal ahead of the front to above average in the low to mid 80s. Probabilistic and ensemble solutions continue to vary widely in the Thu to Sat timeframe with respect to the synoptic pattern. Some ensemble cluster solutions indicate troughing over the MS valley and ridging off the western Atlantic (aka latest GFS/CMC), which would favor warmer highs and help draw northward any disturbance in the Gulf later in the week. Where it tracks though is widely varied. Other solutions show troughing nearby with the aforementioned cold front, keeping rain chances elevated. And still a third solution shows a rex/omega ridge pattern near the OH valley and troughing on either side, which could favor drier conditions to start but also advect any tropical system in the Gulf over the weekend. This is seen in the prior 00z ECMWF. Speaking of the Gulf, NHC now has a 60- percent chance of tropical development late next week over the south- central Gulf. Where the system would move is highly dependent on the pattern discussed above, which is too uncertain, but certainly bears watching, given a wide range of potential impacts. As a result, have kept rain chances low Thu to Sat, with temperatures near to slightly below normal in the upper 70s to near 80. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... As of 138 AM Sunday... A cluster of showers and storms and associated sub-VFR restrictions will impact KRDU and KRWI through 08z, and KFAY through ~10z. In the wake of the convection/rain, some patchy fog and MVFR ceilings may develop around or shortly after daybreak, mainly at KRWI. These sub-VFR ceilings could linger at KRWI into the early afternoon before lifting. Elsewhere, flight conditions should remain VFR. Then during the afternoon and evening, a back-door cold front, denoted by a NELY wind shift, will push southeast through the through the area, bringing widespread LIFR to IFR restrictions in stratus and fog Sunday evening/night. After 06Z Monday: Mainly VFR conditions expected each day, with the exception of sub-VFR fog/stratus each morning. There is a chance for mainly afternoon/evening showers/tstms each day, which could also briefly reduce flt conditions at times. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...CBL NEAR TERM...CBL SHORT TERM...CBL LONG TERM...Kren AVIATION...CBL/np