Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 210827 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 427 AM EDT Sun May 21 2017 .SYNOPSIS...
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Weak high pressure will wedge south into the area as the back-door cold front temporarily stalls across the NC mountains and foothills. The stalled will lift back north-northeast as a warm front late this evening and tonight, in advance of a cold front that will move into the region on Monday.
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&& .NEAR TERM /THROUGH TONIGHT/... As of 355 AM Sunday... The back-door cold front that moved through the area this past evening appears to be in the process of settling in/stalling out across the NC mtns and fthls. In it`s wake, a transitory parent high building over the Mid-Atlantic Seaboard will briefly wedge south into central NC through the early afternoon. As the high lifts out, this will allow the front stalled to our west-southwest to retreat northeastward as a warm front during the late-mid afternoon and into the evening. The majority of the afternoon across central NC will be mostly with just low clouds associated with the shallow CAD regime. The exceptions will be for a few showers across the far western Piedmont in proximity to the stalled front, and near the Sandhills and southern Coastal Plain where partial breaks in the more shallower low-cloud cover will lead to weak destabilization. Expect a sharp northeast-southwest temperature gradient across the area, with the partial breaks in cloud cover across the south/southeast allowing temps to warm into the mid 80s, while the north/northeast entrenched in low clouds, will barely reach the 70s. A series of upper disturbances and strengthening southerly moist warm air advection within a 25kt LLJ spreading east into the area as a cold front approaches the NC mtns, will give rise to increasing shower chances after sunset and overnight, with a rumble of thunder or two as weak instability develops behind the northward lifting warm front. Lows Sunday night 65 to 70. && .SHORT TERM /MONDAY AND MONDAY NIGHT/... As of 415 AM Sunday... Surface cold front over the mtns will inch slowly eastward Monday and Monday night as the amplifying flow aloft becomes increasingly parallel to the low-level boundary. This will set up multiple rounds of convection throughout the day/night, with the lead shower band(s) across the Piedmont Monday morning progressing eastward into the coastal plain during the mid to late morning hours. A second round of convection is expected to re-develop everywhere by the afternoon with daytime heating resulting in moderate instability(1000 to 2000 J/kg) across the area. Modest lapse rates of 5.5-6.0 C/km coupled with bulk shear of only 20 to 25 kts will limit severe threat. Highs ranging from the upper 70s/near 80 west to mid 80s southeast. What once look like a brief lull for Monday night/early Tuesday looks to be setting up for yet another round of showers and thunderstorms with the front hung up over the area as a series of upper disturbances eject NE across through the region, in advance of the digging upstream synoptic scale trough. Instability looks to be marginal, but models suggest increasing deep layer shear Monday night in response to a strengthening mid/upper level jet streak. Additionally, with the front stalled across the area the threat of heavy rain and flooding will begin to increase. Lows Monday night in the 60s. && .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 325 AM EDT SUNDAY... Tuesday through Wednesday: Tuesday looks to be a wet, potentially active weather day, as a mid-level shortwave and accompanying sfc low moving along the boundary that`s stalled across the Carolinas, approaches from the SW and moves across our area during the daytime. Two main concerns exist with this system: 1) potential for heavy rain and subsequent poor draining flooding, and 2) risk for rotating cells should there be enough instability to initiate convection along and south/east of the boundary. Regarding the first concern, it appears that 1-2+ inches of rain will be possible along and just north of the boundary on Tuesday, thanks to vigorous SW flow and moisture transport, over-running low level NE flow along and north of the boundary. Regarding the second concern, models prog an impressive 50+ kt lljet nosing up into the Carolinas from the southwest. While that lljet definitely helps the heavy rain potential, the combination of the boundary, low level shear, and 40- 50+ kt of bulk shear would also suggest the potential for supercells should there be convection along and east of the boundary. However in this case, widespread cloudiness and earlier/ongoing rain will likely limit instability and be a limiting factor for that threat. Nevertheless, both of these concerns will need to be closely monitored. In any event, it appears the that sfc low will move east of I-95 by late afternoon, followed by rain diminishing during evening. The next short wave and assoc sfc low in this active pattern will lift NE across the Carolinas on Wednesday. Look for another round of rain with this wave, and similar to Tuesday, should there be enough instability to initiate convection, the shear would suggest potential for severe storms, including rotating cells. While the boundary and sfc wave positions and shear profiles raise quite a bit of concern, perhaps the more likely concern both Tuesday and Wednesday will be the risk for heavy rain and flooding. It`s worth noting that the ECMWF and GFS suggest 2-day rainfall amounts of 3+ inches, possibly higher per the GFS. Temps both days will be limited by cloudiness and rain. Highs in the low 70s. Lows around 60. Thursday: The trough axis will move across the Carolinas. Resulting mid level cooling and subsequent instability will result in scattered showers, but with much lower QPF values (less than 1/2 inch). With breaks in the clouds and some sun, look for temps to rebound some...highs in the upper 70s. Friday and Saturday: Look for things to finally dry out with moderating temps as a short ridge builds across the area. Highs returning to the 80s and lows in the lower 60s. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... As of 210 AM Sunday... Weak high pressure will wedge south into the area behind the back- door cold front that is forecast to stall across southwest NC today. Post-frontal IFR-MVFR CIGS, developing within the NELY low-level flow will continue to spread west through 09z. These ceilings will generally persist through the forecast period, with any improvement expected to be temporary with ceilings lowering Sunday evening/night with scattered showers overspreading the area as the front retreats back north as a warm front. KFAY is the mostly likely to see some low-end VFR ceilings this afternoon. Outlook: Showers and a few thunderstorms with IFR to MVFR CIGS and VSBYS are expected Sunday night and Monday as a slow moving cold front moves over the region. This cold front will then stall across the region through late in the work week, bringing a prolonged period of adverse aviation conditions in heavy rain and storms as numerous waves track along the front. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...CBL NEAR TERM...CBL SHORT TERM...CBL LONG TERM..np AVIATION...CBL

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