Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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084 FXUS62 KRAH 182349 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 750 PM EDT Wed Sep 18 2024 .SYNOPSIS... A weak area of low pressure off the Mid-Atlantic coast will lift northeast through Thursday and be replaced by high pressure that will gradually build into central North Carolina through the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 240 PM Wednesday... A weakening mid/level low churning over upstate SC this afternoon will slowly sag southeast through SC and southern NC before transitioning into a broad open wave over the Mid-Atlantic by Thurs morning. At the surface, an area of low pressure off the NC/VA coast this afternoon is expected to gradually deepen through the overnight hours. In the process, an area of richer theta-e air over southeast VA and northeast NC, characterized by dew points in the 70s and temps in the 80s, will sag south this afternoon within a weak pressure trough and northerly wind shift. Diurnal heating of the richer theta-e airmass oozing into the northern Coastal Plain and northeast Piedmont will result in weak to moderate instability to develop (1000-1500 J/kg MLCAPE) by the early afternoon. Weak convergence along the front and little inhibition through the troposphere should result in scattered showers and isolated thunderstorms. Hi-Res guidance shows this area will continue to spread southward through the early overnight period. Organized storm mode is not expected as central NC is nestled in a weakness in the 500mb flow and results in light, erratic winds through the lowest 500mb. Additional showers and isolated storms will be possible over the southern Piedmont, Sandhills, into the southern Coastal Plain associated with the weakening mid-level vort max as it drifts just south of this area. Hi-Res guidance suggests that a weakly stable airmass will remain in place over central NC for most of the night and will likely continue some isolated showers through midnight with gradual weakening/dispersing thereafter. Thick and low overcast will overspread the area from north to south through the overnight hours. Some patchy fog may be possible early Thurs morning as cloud bases briefly lower, but guidance has lowered probabilities of fog in favor of mostly stratus. Overnight lows will settle in the mid/upper 60s for most areas. && .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/... As of 305 PM Wednesday... Aloft, the trough situated over the East Coast should slowly slide eastward through Thu night, but remain along/just off the East Coast by Fri morn as high pressure builds over the Plains and MS Valley. At the surface, a low will meander off the northern mid-Atlantic/New England Coast Thu/Thu night, while high pressure over the ern Great Lakes ridges swd along the Appalachians. Meanwhile, the low that has lingered over the northeast NC coast should shift esewd but linger just off the central NC coast Thu before moving further southeast over the Atlantic. Expect generally nly/nely flow across central NC through Thu night. Some showers may linger into Thu morning over the Piedmont. There could be a brief lull in activity before additional scattered showers and isolated storms develop Thu aft, mainly along lingering surface boundaries. Skies may remain mostly cloudy through Thu morn and into the aft, which could further limit daytime heating. Highs should top out in the mid 70s to low 80s, but could be a couple/few degrees higher if cloud cover decreases earlier that forecast. While the weather should dry out, there should be lingering partly to mostly cloudy skies Thu night, with lows expected to range from upper 50s north to mid 60s south. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... As of 245 PM Wednesday... Overall, the surface pattern for the extended forecast period should be relatively quiet. At the beginning of the period, high pressure will be over eastern Canada with a ridge extending to the southeast across the Carolinas. This will change little through the period until a cold front approaches the Appalachian Mountains on Wednesday. However, at mid/upper levels, there will be occasional ripples of energy moving across the western half of North Carolina. Friday through Tuesday all show minimal precipitation clipping the Triad in the ECMWF and GFS ensembles, yet with the exception of Monday, the deterministic models don`t show any precipitation during that time period. Having inherited a dry forecast and seeing little conclusive evidence in the models, am inclined to keep the forecast dry. However, Will go ahead and put in slight chance pops to the forecast for Wednesday afternoon across northwestern counties for the new day 7 forecast with the approaching front. Normal temperatures for late September are around 80 and 60 - forecast values are slightly above average for Friday through Sunday, then near average for Monday through Wednesday. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... As of 750 PM Wednesday... VFR conditions are largely expected to start the TAF period. The one exception will be at FAY, where isolated storms have developed within 5 miles of the terminal. These storms are expected to weaken over the next few hours, but included a TEMPO for IFR conditions in the immediate near-term. A trend from VFR to IFR and then LIFR is expected to commence with the passage of a surface boundary draped along the NC/VA border. These conditions are expected to develop across the northern terminals (GSO/INT/RDU/RWI) between 03 and 06z and between 08-11z at FAY. These IFR/LIFR conditions are largely favored to be driven by low ceilings. However, some recent guidance suggests patchy fog possible at FAY, perhaps due to storms saturating the low-levels prior to the boundary passage. Confidence on this is low but included a TEMPO for these LIFR conditions. There could be some isolated storms early Thu near RDU/RWI, with confidence highest at RDU. Aviation conditions should lift to MVFR around 15-18z and gradually become VFR by the late afternoon. The surface boundary will linger over the area Thu and will favor widely isolated storms, most favored at FAY/RWI and perhaps RDU. Outlook: Areas of overnight and early morning stratus will remain possible Fri and Sat mornings. Aviation conditions should largely trend VFR Sun and Mon. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Swiggett NEAR TERM...Swiggett SHORT TERM...KC LONG TERM...Green AVIATION...Kren