Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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872 FXUS62 KRAH 231755 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 155 PM EDT Mon Apr 23 2018 .SYNOPSIS... Strong high pressure will remain nearly stationary or slowly drift off the New England coast through tonight. Low pressure will approach from the Tennessee Valley tonight, then track slowly east over SC on Tuesday before lifting northeast across eastern NC late Tuesday and Tuesday night. && .NEAR TERM /THROUGH TONIGHT/... As of 1050 AM Monday... Little adjustment required to the near term forecast. 12Z upper air analysis depicts a stout se flow in the lowest 10k ft of the atmosphere. This flow expected to strengthen later today into tonight as the pressure gradient tightens between a sfc low immediately to our west-southwest to a strong high offshore of New England. Sustained sfc winds 15-20 mph probable with gusts around 30 mph common. This fetch off of the southern Atlantic will pull abundant moisture into the region. This available moisture in conjunction with lift provided by an approaching s/w and central NC in the favored left exit region of a 80-90kts crossing the Deep South will result in bands of moderate to locally heavy rainfall across the region this afternoon, through tonight. Rainfall amounts on the order of one-two inches look reachable. The rain encroaching upon central NC from the southwest will cause temperatures to hold steady this afternoon roughly south and west of Raleigh, while temperatures should continue through mid afternoon for locations north and east of Raleigh. Temperatures will change little this evening into the overnight, ranging from the low-mid 50s NW to the upper 50s SE. && .SHORT TERM /TUESDAY AND TUESDAY NIGHT/... As of 350 AM Monday... An elongated srn stream mid-upr low over the mid-South this morning is forecast to wobble to near Nashville, TN by 12Z Tue and to swrn VA by 12Z Wed. Preceding the upr low, the right entrance region of a strengthening sly to ssely, 80-100 kt upr level jet will stream across e-cntl NC and sern VA through 18Z Tue. Associated divergence aloft, atop a strong low level WAA/isentropic upglide regime courtesy of a 40-45 kt low lvl jet, will support ongoing widespread rain and embedded elevated convection (showers), early Tue. This regime will lift newd into and offshore VA through early afternoon, followed by a mid level dry slot that will nose across the Carolinas Tue afternoon and evening. At the surface, the models indicate a triple point low over nern GA/wrn SC at 12Z Tue will track newd into the srn NC Piedmont/wrn Sandhills by 00Z Wed, then track nnewd roughly along US Highway 1 Tue night. A preceding warm front will arc enewd across srn and sern NC early Tue, with the trailing cold front extending swd along the srn SC and GA coast. The cold front is forecast to progress ewd more quickly than the warm front retreats nwd, with an associated increasingly narrow wedge of warm sector characterized by low-mid 60s surface dewpoints and mainly weak sfc-based instability, which is forecast to pivot newd across nern SC and ern and e-cntl NC Tue afternoon, beneath the aforementioned mid lvl dry slot. Low lvl and deep layer flow will have weakened considerably and veered in the wake of the early day WAA/isentropically-driven rain, though lingering effective SRH on the order of 100-150 m2/s2 immediately preceding the surface wave may support episodic low level rotation in showers/storms late Tue aft-evening. However, a lack of more appreciable instability and shear suggests any severe weather threat over cntl NC should be limited. Showers will linger Tue night, particularly over the Piedmont, as the mid-upr low and associated cold pool aloft pivot overhead. Temperatures Tue are expected to range from low-mid 60s in a lingering damming regime over the NW Piedmont (nw of the track of the surface low), to low-mid 70s across the Sandhills and srn-cntl Coastal Plain, with lows in the 50s. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... As of 150 PM Monday... An active, energetic upper pattern featuring a long wave trof over the eastern CONUS will persist from mid week into the weekend. There is a lot of uncertainty regarding the timing and potential for phasing of a couple of short waves which will be digging into the longer wave pattern, which will ultimately determine the potential for their producing rain over central NC. A reinforcing, but dry, cold front will be pushed southeast through the area on Wednesday into Wednesday night as our initial upper low lifts northeast to be absorbed by a stronger cutoff low moving across the Great Lakes. There will be a small chance of showers across the northern tier of the area, with highs Wednesday in the low to mid 70s. Lows Wednesday night will be in the low and mid 50s. Skies will be at least partly sunny on Thursday with cooler highs in the upper 60s to lower 70s as the cold front stalls across the Gulf states. A southern stream short wave moving across the Gulf states Thursday night will spur development of a surface wave along the front, which could slide east along the front and offshore or possibly lift more northeasterly into the area and produce showers on Friday. Highs will be below normal regardless, ranging from 70 to 75, possibly cooler if we get significant shower coverage. All this while, the primary long wave upper trof has been edging east, and the trof axis will pass over the area on Saturday, possibly squeezing out a final few showers. Highs Saturday will be in the upper 60s to lower 70s. Heights finally begin to build late in the weekend as upper ridging moves into the Midwest, with strong sunshine as the associated surface high builds over the area. Highs Sunday will be in the low to mid 70s, with mid and upper 70s expected on Monday. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... As of 155 PM Monday... There is high confidence that aviation conditions will deteriorate to IFR/LIFR ceilings this evening, persisting through Tuesday morning. Additionally, widespread showers will cover the region ahead of a sfc warm front that will gradually lift nwd across SC this evening, and into central NC overnight through Tuesday morning. The presence of this warm front will create low level wind shear conditions, primarily at KRDU, KFAY, and KRWI. While sfc winds will be east-northeast 15-20 mph with gusts around 30 mph, winds at 2000 ft are forecast to be sely around 45 mph. These low level wind shear conditions are expected to diminish after 15Z Tuesday. Aviation ceilings will slowly improve to MVFR ceilings through Tuesday afternoon. A few thunderstorms may develop during the the late morning into the afternoon. MVFR/low end VFR ceilings appear likely across central NC Tuesday night into Wednesday. VFR parameters will most likely occur through Friday with brief instances of MVFR conditions probable. The next threat for widespread MVFR ceilings appears to be late Friday into Saturday as an area of low pressure affects the region. && .RAH WATCHES/WARNINGS/ADVISORIES... NC...None. && $$ SYNOPSIS...Badgett/Hartfield NEAR TERM...WSS SHORT TERM...MWS LONG TERM...MWS AVIATION...WSS

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