Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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740 FXUS62 KRAH 291831 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 230 PM EDT Mon May 29 2017 .SYNOPSIS... An unsettled pattern associated with cyclonic flow aloft will persist through mid-week. && .NEAR TERM /THROUGH TONIGHT/... As of 115 PM EDT Monday... A plume of enhanced 925-850 mb moisture advecting into central NC from the W/SW amidst strong insolation and modest mid-level lapse rates (~6.0C/km) is expected to yield 1000-1500 J/kg MLCAPE with no CINH by peak heating this afternoon. W/regard to forcing, numerous perturbations were noted in WSW flow aloft upstream of the Carolinas at 17Z. A series of the aforementioned disturbances are progged to track ENE across the Carolinas this aft/eve into tonight. In the lower levels, a developing thermal trough over the NC Piedmont this afternoon should help serve as a focus for development once CINH has eroded, particularly if a weak/broad low forms over central SC/NC as some of the latest 12Z guidance suggests. With the above in mind, expect convection to develop across the W/SW Piedmont by late afternoon. Given an environment characterized by steep low-level lapse rates (0-3km ~8c/km) and moderate DCAPE (~1000 J/kg) in a westerly flow regime, it seems likely that convection will grow upscale along outflow and propagate east across central NC by late evening (~03Z), with the relative best chance along/south of Hwy 64. Additional convection is progged to develop over southwest NC/upstate SC (upstream of the initial activity) this evening as additional disturbances in WSW flow aloft track across a moist /conditionally unstable/ airmass in place over the region. As a result, it is possible that convection could persist past midnight into the 06-09Z time-frame, primarily along/south of Hwy 64. Deep layer shear and moderate destabilization will be sufficient for supercellular organization with initial activity that develops this aft/eve, with a primary threat of damaging winds and severe hail (the latter of which may be tempered by modest mid-level lapse rates). With steep low-level lapse rates and moderate DCAPE expected this afternoon, activity is likely to grow upscale along outflow with time. This suggests the primary severe threat will transition to damaging winds late this afternoon and early evening. Expect highs ranging from the mid 80s far NW Piedmont to lower 90s Sandhills and SE Coastal Plain. Lows tonight in the 60s, coolest N/NW and warmest S/SE. -Vincent && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
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As of 230 PM Monday... Tuesday and Tuesday night: Upper low over Ontario will move very little over the next couple of days, with a gradual NEWD wobble over James Bay region by Tuesday night. The evolution of this evening/tonight`s convection may leave behind a surface trough/thermal-moisture boundary across eastern/southeastern NC, while also serving to modulate buoyancy due to convective overturning. So will have to wait and see how that plays out as models show weak to to moderate instability developing Tuesday afternoon in response to strong insolation/steep low-level lapse rates. While insolation alone could allow for some isolated convection to develop across central NC, the primary convective trigger Tuesday afternoon/evening will be with any shortwave impulse(s) or MCV(s) ejecting NEWD from the MCS blob currently over the western GOM. POPS/rain chances look to range from slight to small chance across the NW to good/high chance across the east. While, deep layer shear won`t be as favorable as in previous days, 30-35 kts will still be sufficient to support a few strong to severe multicell clusters during peak heating. Highs ranging from lower to mid 80s north to mid/upper south, high dependent on convective evolution. Lows in the lower 60s NW to upper 60s/near 70 south. Wednesday and Wednesday night: The closed low over Ontario/James Bay will get reinforced by another closed cyclone diving SE out of central Canada. Shortwave energy rotating through the base of the mean trough will push a cold front into the region from the northwest Wednesday evening/night, which will allow for a continued threat of scattered showers and storms area-wide Wednesday. Pre- storm environment in place across central NC on Wednesday will be very similar to Tuesday, thus a few strong to severe storm clusters are possible, especially across the NW Piedmont where arrival of low- level frontal zone will better coincide with more favorable diurnal timing. Highs in the mid to upper 80s. Lows slightly cooler below the front. Lows around 60 NW to mid 60s SE.
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&& .LONG TERM /THURSDAY THROUGH MONDAY/...
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As of 230 PM EDT Monday... Weak high pressure building into the area in the wake of the cold frontal passage Wednesday night, will advect drier more stable air advecting in from the WNW, potentially keeping central NC convection free on Thursday. However, these dry conditions look to be short- lived with the return of moist low-level SWLY and potential shortwave disturbances ejecting east from the Southwest US. Rain chances look to increase even further through the weekend, in response to height falls aloft and under the increasing influence of cyclonic flow aloft as the the upper trough amplifies across the NE US, sending a cold front southward into the region late Saturday and into Sunday. Temperatures should hover around normal, falling to below normal on Monday as high pressure builds into the region from the northwest.
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&& .AVIATION /18Z MONDAY THROUGH FRIDAY/... As of 115 PM EDT Monday... 24-HR TAF Period: VFR conditions will prevail through mid to late afternoon at all terminals. Sub-VFR conditions associated with scattered convection are expected late this afternoon and evening, primarily at southern/eastern terminals (FAY/RDU/RWI) with the relative best potential at the FAY terminal. Convection could persist past midnight (into the 06-09Z time frame), though once again it would appear that southern/eastern terminals are more likely to be affected. In areas that experience rain, a short period of IFR/LIFR ceilings or fog could develop prior to sunrise if skies clear, though whether or not this will occur remains difficult to ascertain at this time. Looking Ahead: Aside from a potential for isolated to scattered afternoon and evening convection associated with cyclonic flow aloft over the region, expect VFR conditions to generally prevail through mid to late week. -Vincent && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Vincent NEAR TERM...Vincent SHORT TERM...CBL LONG TERM...CBL AVIATION...Vincent

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