Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 280905 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 404 AM EST Tue Feb 28 2017 .SYNOPSIS... A warm front lifting through the area this morning will result in a mild southerly wind through Wednesday. A strong a cold front will cross the area Wednesday night. && .NEAR TERM /THROUGH TONIGHT/... As of 330 AM Tuesday... The 00z/28TH showed pretty decent warm advection in the low levels, with a pronounced warm front just inland from the Carolinas coast early this morning. A sheared disturbance aloft is exiting the coastal plain, taking most of the high clouds with it. A few showers have broken out south and east of FAY in the past couple hours in response to the warm advection, though hires guidance tends to keep the best isentropic lift focused east of I-95, and any stratus looks to be fairly thin if it develops in the next few hours. The warm front will lift through the area this morning and yield a southerly wind with 1000-850mb thicknesses reaching around 1385m, suggesting highs well into the 70s to around 80. Mid- level lapse rates steep to 6.5-7 C/km this afternoon, but strong warm near 850mb also creates a modest cap, per forecast soundings, which will be hard to break given low-amplitude southwest flow aloft and no good trigger for convection. However, guidance is in pretty good agreement on the remnants of convection on the Tenn Valley clipping the northwest Piedmont after ~22Z, though generally remaining west of the better destablization and limiting any thunder this evening. Chance POPs will accordingly be highs in the northwest this evening. Expect stratus overnight in a steady 5-10kt southerly flow, resulting in very mile lows in the 60s. && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... As of 400 AM Tuesday... Wed-Wed night: A complex mid-upper level trough compromised of multiple embedded shortwave perturbations will move E from the Plains states early Wed to the Northeast by Thu morning. At the same time and at the surface, related waves of low pressure will migrate from the mid MS Valley to New England, while the trailing cold front will move from the Appalachians late Wed-Wed evening to the Atlantic coast by Thu morning. It will be warm and windy, but dry for most of the day Wed, owing to a stout capping inversion that will be only gradually lifted and eroded Wed afternoon, in response to height falls accompanying the aforementioned trough aloft. 925 mb wind progs and BUFR forecast soundings indicate strong SWly flow will develop in the warm sector, with sustained winds of 20-25 mph and gusts to around 40 mph. Morning stratus, trapped beneath the aforementioned inversion, will disperse by midday or early afternoon, so temperatures should consequently rise rapidly into the upper 70s to lower 80s. Pre- frontal showers and storms will be possible over the far wrn Piedmont, where the aforementioned removal of the preceding cap will be most likely by around sunset. The better chance of showers and storms will occur Wed evening and early Wed night, as frontal forcing accompanying the surface front sweeps Ewd. Strong SWly deep layer flow, oriented mainly parallel to the frontal zone, will favor linear convection --amidst an environment characterized by around 250-750 J/kg of CAPE-- that would pose primarily a damaging wind threat from both momentum transport and mesovortices embedded within a probable broken band or two of convection. An isolated tornado will also be possible, given the degree of low and deep layer shear, though a a relative lack of more robust instability suggests damaging winds will prove a greater threat. Blustery post- frontal NWly winds will follow in strong CAA late Wed night- early Thu, with lows in the low- mid 40s west to middle 50s east. && .LONG TERM /THURSDAY THROUGH MONDAY/... As of 345 AM Tuesday... A broad trough aloft will migrate across the eastern U.S. during the end of the week, and reach maximum amplitude as a shortwave trough in NW flow aloft amplifies into the Middle Atlantic states during the day Fri. Considerable high cloudiness, within the axis of a 150 kt WSWly upper level jet, will stream across NC on Thu, before the S of our region Thu night. Downslope NWly flow will help offset waning CAA. MOS high temperatures typically perform well in such downslope regimes, with upper 50s to lower-middle 60s anticipated. A reinforcing nrn stream surface cold front will accompany the aforementioned shortwave trough in NW flow aloft; and this front will approach from the NW Thu night, then sweep across central NC during the day Fri. Downslope flow will again develop behind the reinforcing front on Fri, so MOS temperatures in the middle 50s to lower 60s are favored. Cold and dry advection within a deeply mixed (800-750 mb) boundary layer will support afternoon wind gusts around 30 mph. Fri night through Mon: The trough will have moved offshore by this weekend, with increasingly zonal flow aloft and/or broad/flat ridging across the srn and sern U.S. Temperatures will consequently moderate into the 70s by Mon, after a probable hard freeze with excellent radiational cooling of a fresh 1030-1035 mb cP surface high 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. && .AVIATION /08Z TUESDAY THROUGH SATURDAY/... As of 100 AM Tuesday... VFR conditions prevail at 06Z/28th as high clouds continue to move east across the area. An area of showers south of CHS should remain confined to coastal SC, but the advancement of a warm front and southeasterly low level flow may bring some MVFR stratus north into southern and western NC. Models seem to indicate late development of MVFR ceilings with fairly thin moisture, with higher confidence at FAY, INT and GSO after 09. there are some MVFR ceilings already developing south of VUJ, which lends some confidence to the forecast through early morning. What stratus that does develop should be quick to disperse and give way to VFR (or near MVFR) ceilings this afternoon and some southwesterly wind gusts to near 20kt). Some showers will be possible near INT and GSO late this afternoon and evening as an impulse and associated convection move through the Tenn Valley and across the mountains, which could result in a brief period of sub-VFR conditions. Outlook: Sub-VFR ceilings, most likely IFR, are expected late tonight, along with low-level wind shear, as a 40-50kt low level jet traverses the area. Wind gusts around 30kt will develop on Wednesday ahead of a strong cold front and eventual line of strong to severe storms that will cross the area Wednesday evening/night. VFR will return on Thursday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...SMITH NEAR TERM...SMITH SHORT TERM...MWS LONG TERM...MWS AVIATION...SMITH

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