Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 011101 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 558 AM EST Wed Mar 1 2017 .SYNOPSIS... Warm southwest flow will continue across the region today ahead of a strong cold front approaching from the west. The cold front will cross the area tonight, followed by cool high pressure for the latter half of the week. && .NEAR TERM /THROUGH TONIGHT/... As of 320 AM Wednesday... Big stories today will be near record heat and potential for severe storms this evening... Deep southwesterly flow downstream of a trough over the Plains will likely result in record highs as 1000-850mb climb to 1395m, which suggests upper 70s to mid 80s. High clouds are thinning out this morning and should remain fairly thin for most of the day before deeper moisture moves with the cold front and convection this evening. Wind gusts of 30-40kt are also expected, the strongest of which may be over the northern coastal plain through midday as mixing taps into a departing low level jet, which VWP indicates is around 50kt. 925mb and 850mb winds relax during the day before strengthening again as the pressure gradient tightens ahead of the front, so gusts should remain below Wind Advisory criteria. The warming and steepening mid-level lapse rates -near 7.5 C/km- will yield some modest MLCAPE this afternoon, but a fairly prominent capping inversion and CINH should inhibit prefrontal convection until the upstream squall line over IN/IL/MO/AR and strong height falls arrive this evening. Despite poor diurnal timing -between 8pm and midnight per most hires guidance- and the squall line having to cross the mountains, forecast soundings show up to 1000 j/kg MLCAPE and a 2-3hr window with a weakened cap where the CAPE/shear parameter space would support sustained convection. Wind damage is the main concern given linear forcing and 50kt ambient winds, particularly into the coastal plain, though hail is also likely with an elevated mixed layer. The tornadic threat is much smaller owing to long straight hodographs, but subtly veering and the strength of the flow may lead to some curvature and the possibility of embedded mesos along the line. the SPC day 1 Outlook was essentially unchanged and includes all of central NC in a Slight Risk. Expect rapid clearing behind the line after midnight, with temps falling into the 40s and lower 50s. && .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/... As of 400 AM Wednesday... After lingering mid level ceilings and perhaps a few sprinkles over the far sern counties early Thu, cirrostratus within the axis of a 150 kt WSWly gradually edge Swd and out of central NC throughout the day. Downslope NWly flow will help offset waning CAA. Highs in the upper 50s to lower-middle 60s, with gusts up to 25 mph until midday- early afternoon, before CAA diminishes by afternoon. Surface high pressure will ridge overhead from the SW in advance of a clipper frontal system approaching from the NW, so temperatures will have the potential cool into the upper 20s to lower-middle 30s. Thu night. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 355 AM Wednesday... A progressive pattern aloft will result in a transition from a departing trough in the eastern U.S. Fri-Sat, to ridging through early next week. The trough will reach maximum amplitude as a shortwave trough in NW flow aloft amplifies across the Middle Atlantic states during the day Fri. This trough will be followed by a less amplified/shear vorticity maximum that will migrate through the NW flow, with a brief period mid level WAA cloudiness, on Sat. At the surface, a clipper surface wave accompanying the aforementioned shortwave trough in NW flow aloft will track across the nrn Middle Atlantic states, while the trailing nrn stream surface cold front will sweep across central NC during the day Fri. Given both 1) a tendency for the models to advect cold air across the Appalachians too quickly, and 2) the prevalence of a downslope/compressional warming flow component throughout the day, temperatures are expected to recover into the middle 50s to lower 60s. Cold and dry advection within a deeply mixed (800-750 mb) boundary layer will support afternoon wind gusts up to 25-30 mph, which will make it feel cooler. Incoming cP surface high pressure behind the front on Fri will result in a hard freeze Fri night-Sat morning, when temperatures are expected to fall into the lower-middle 20s over the Piedmont, to upper 20s to around 30 degrees over the Sandhills, srn Coastal Plain, and urban areas. Temperatures will gradually moderate thereafter, as the surface ridge moves E and modifies, with 50s on Sat replaced by 60s-70s by early next week. After a dry weekend as the ridge moves overhead and offshore, the approach of the next frontal system will result in a chance of showers late Mon-Tue. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... As of 1235 AM Wednesday... Strong winds expected today, with storms late this evening... Despite a weakening band of light showers crossing the area, conditions are VFR at most all terminals early this morning. Stratus has formed over much of eastern SC and southeastern NC, and southerly flow will cause the IFR ceilings to spread north across central and eastern NC over the next few hours, impacting mainly RDU/FAY/RWI, with greatest confidence at FAY and RWI between 08Z and 14Z. Forecast soundings also suggest low level wind shear is possible through 12Z, moreso at GSO and INT where the surface inversion is strongest, as a 40-50kt low level jet translates across the area. However, surface winds will also be increasing overnight and near surface mixing may mitigate the intensity and/or duration of the LLWS. VFR is expect to day with strong southwesterly winds that will likely gust to around 35kt at time. A line of strong/severe storms will move into the areas from the west this evening, with may locally enhance wind gusts and cause a period of sub-VFR, primarily between 2/00Z and 2/06Z. Outlook: Skies will clear out for Thursday with VFR conditions and NW winds. VFR conditions will hold Thu through Sun as high pressure builds over the area. && .FIRE WEATHER... As of 550 AM Wednesday... Critical, or nearly so, fire weather conditions still probable Thu and especially Fri. Much drier air will overspread central NC following a cold frontal passage, and accompanying line of showers and storms, tonight. The drier air, combined with afternoon temperatures in the upper 50s to middle 60s on Thu, will result in minimum relative humidity values between 20 and 25 percent Thu afternoon. However, NWly winds, which will gust between 20-25 mph through 1 PM, will subside during the afternoon (when critical RH values are met). Nonetheless, there may be a several hour period centered around noon Thu when marginally critical relative humidity values between 25-35 percent overlap with the aforementioned stronger winds; and increased fire danger may result. These conditions will also set the stage for Fri, when daytime heating and a secondary cold frontal passage during the afternoon will result in critical RH values for several hours during the afternoon. In addition, breezy Wly to NWly surface winds are forecast to be sustained between 15-20 mph, with 25-30 mph gusts. These conditions for increased fire danger to red flag will likely be coordinated with the NCFS later today and/or on Thu. && .CLIMATE... Record highs for March 1st: RDU: 82 (set in 1997) GSO: 77 (set in 2012) FAY: 87 (set in 1918) && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...SMITH NEAR TERM...SMITH SHORT TERM...MWS LONG TERM...MWS AVIATION...SMITH FIRE WEATHER...MWS CLIMATE...RAH

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