Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 282334 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 733 PM EDT Sun May 28 2017 .SYNOPSIS... A series of upper level disturbances will track east across the Carolinas this afternoon through Monday evening. && .NEAR TERM /THROUGH TONIGHT/... As of 200 PM EDT Sunday... The EML in place over the Carolinas the past few days has been modified and suppressed southward by numerous rounds of convection over the past 24 hours, with H7-H5 lapse rates ranging from ~5.5c/km near the VA border to 6.0-6.5C/km near the SC border. Diurnal destabilization this afternoon is expected to range from marginal (~500 J/kg MLCAPE) near the VA border to moderate (1500-2500 J/kg MLCAPE) near the SC border where the strongest insolation and richest low-level moisture will be juxtaposed with mid-level lapse rates on the order of 6.0-6.5c/km. With numerous MCVs upstream of the Carolinas, significant uncertainty persists with regard to the timing/coverage of convection this aft/eve. Convection allowing models such as the 12Z HRRR and NAM NEST suggest scattered convection will develop over western NC around ~21Z and propagate east across central NC through ~03Z this evening, presumably in association with one of several MCVs expected to track across portions of the Carolinas. Moderate destabilization, effective shear on the order of 40-50 knots, straight hodographs, and relatively steep mid-level lapse rates across the SW Piedmont/Sandhills suggest the primary mode of convection (should it develop) will be splitting supercells with an attendant threat for large hail (1.00-1.75"). Damaging winds cannot be ruled out, however, the environment in place across central NC today is significantly less supportive than in previous days (DCAPE 500-750 J/kg (primarily near the SC border) this afternoon. Diurnal destabilization will be weakest north of Hwy 64, particularly in the NE Coastal Plain where weak mid-level lapse rates will be juxtaposed with a cooler airmass in vicinity of a stalled front near the VA border. With the above in mind, a conditional potential for splitting supercells will exist later this aft/eve, with a primary threat of severe hail (1.00-1.75"). Expect highs this afternoon to range from the lower 90s near the SC border to the lower 80s near the VA border in the Northern Piedmont and NE Coastal Plain. Lows tonight should range from the mid/upper 60s near the VA border to lower 70s near the SC border. -Vincent && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 300 PM Sunday... Monday and Monday night: The closed low over the Upper Great Lakes will wobble slowly east on Monday. The primary northern stream shortwave trough is expected to weaken as it lifts northeast away from the area, shearing out across the northern Mid-Atlantic and NE U.S., with attendant trailing sfc cold front expected to stall out across the area late Monday into Monday night. The arrival of this front into the area Monday afternoon/night coupled with individual perturbations ejecting NEWD in the broad cyclonic flow, along the southern fringes of the strong belt of westerlies, will bring another round of showers and thunderstorms to the area that could linger well into the overnight hours as the front begins to stall out. Strong daytime heating within the moist and moderately unstable airmass combined with continued strong mid-level flow that will support favorable/strong deep layer shear of 40-45 kts, will result in another slight risk for severe storms across the area with damaging winds and large hail the primary threats. Storm intensity should weaken significantly with loss of daytime heating, so the severe threat should fall between 2 to 10 pm. Highs in the mid 80s north to lower 90s south. Lows Monday night will depend on the location of the front, ranging from lower/mid 60s NW to lower 70s SE. Tuesday and Tuesday night: As the upper low continues to wobble slowly eastward over southern Ontario/Upper Great Lakes, the quasi- stationary frontal zone and attendant axis of deeper moisture bisecting central NC Tuesday morning will inch ever so slightly east/southeastward through Tuesday night/early Wednesday. Any shortwave energy moving through the upper jet streak extending from the Tn Valley into the Mid-Atlantic region could result in a convective flare-up and locally heavy rain near the front. As such, expect areas south of east of the Triangle to see the highest rain chances Tuesday afternoon and evening. While, deep layer shear won`t be as good as in previous days, 30-35 kts will still be sufficient to support a few strong to severe multicell clusters during peak afternoon heating. Highs ranging from lower to mid 80s north to upper 80/near 90 south. Lows in the lower 60s NW to upper 60s/near 70 south. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... As of 245 PM EDT Sunday... General model consensus for the mid to late week period is that the closed low over Ontario and associated northern stream trough will get kicked east-northeastward late Wednesday, only to get replaced by a reinforcing closed cyclone diving SE out of central Canada. The eastward progression of the lead trough passage through the NE U.S. and Mid-Atlantic States late Wednesday will push another cold front from the northwest late Wednesday afternoon and evening, which will allow for a continued threat of showers and storms area-wide Wednesday. West-northwesterly flow in the wake of the trough passage on Thursday, may be just enough to push the front south of the region with drier more stable air advecting in from the west, potentially keeping central NC convection free on Thursday. However, these dry conditions look to be short-lived with low-level SWLY flow in advanced of a phased shortwave trough approaching from the west, marking the return of higher humidity and instability, along with the daily chance of mostly diurnal convection Friday and into the weekend. Seasonable temperatures Wednesday and Thursday will return into the above normal ranges by the weekend. && .AVIATION /00Z MONDAY THROUGH THURSDAY/...
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As of 732 PM EDT Sunday... 24-HR TAF Period: VFR conditions will prevail through the period. Isolated convection could impact all sites over the next several hours before diminishing across the area tonight. Potential at any particular site is too low to mention at this time. Winds will remain from the SW at 5-10 kts. Looking ahead: Aside from a potential for isolated/scattered diurnal convection during the afternoon/evening hours each day, VFR conditions are expected to prevail through mid-week. -Vincent
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Vincent NEAR TERM...Vincent SHORT TERM...CBL LONG TERM...CBL AVIATION...30/Vincent

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