Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 210257 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 927 PM EDT Thu Jul 20 2017 .SYNOPSIS... An upper level ridge will build east over the region through Saturday. A cold front will approach late in the weekend and early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 915 PM Thursday... Isolated pulse convection across the SW Piedmont will continue to fade, leaving the remainder of the evening and overnight dry with mostly clear skies with only a few cirrus expected overnight. Lows 70-75. && .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... As of 915 PM Thursday... With the exception of my NW Piedmont counties, most of the CWA will have heat indices of 104 to 107 for several hours tomorrow afternoon. Even if the piedmont counties fall just short(potentially due to dewpoints mixing out into the upper 60s), when considering the cumulative effects of a 3 day heat episode that will begin tomorrow, the stress/impacts will be significant to the area. Thus, will issue Heat Advisory for the Sandhills, eastern Piedmont counties, including the Triangle, and the coastal plain counties, beginning at noon tomorrow and going through 8 pm. Previous discussion: The upper ridge is forecast to peak Friday. The issue will be the heat. After coordinating with surrounding NWS offices, it was decided to hold off on a Heat Advisory for Friday. However, it will be further analyzed tonight as the advisory can be issued in the first or second period of the forecast. Forecast highs of 95 NW to near 100 in the Sandhills still is on target. Dew point forecasts are generally in the lower 70s in the Coastal Plain, and this may be too low. There has been mixing this afternoon over the Piedmont yielding surface dew points in the mid to upper 60s, yet the southern and eastern zones in the Southern Piedmont and Coastal Plain have not mixed out as much with dew points as high as 74 at FAY and 75 at Clinton. FAY had a heat index of 107 at 200 PM today. So, a heat advisory will most likely be needed for a portion of the Coastal Plain and Southern Piedmont on Friday. POP should continue 10 percent or less with strong upper ridging and the MCS activity expected to stay northwest of the region. However, models do point toward increasing chance of mountain storms potentially drifting into the Piedmont late Friday and Friday night. Lows Friday night should stay in the 70s all areas. && .LONG TERM /SATURDAY THROUGH THURSDAY/... As of 245 PM Thursday... Overview: At the beginning of the weekend central NC will be situated in a weakness between a de-amplifying ridge over the central/lower MS river valley and a downstream ridge offshore the SE Coast, along the southern fringe of the westerlies. Cyclonic flow aloft is progged to strengthen over the region late this weekend/early next week, transitioning to NW flow aloft mid-week as an amplifying ridge over the Rockies shifts east into the Central Plains. Long range guidance is in relative good agreement on the overall synoptic pattern, though significant uncertainty persists with regard to the evolution of upstream convection in addition to whether or not shortwave energy may cut-off over the Southeast US early/mid next week. Sat/Sun: Above normal temperatures in the mid/upper 90s are expected over the majority of central NC this weekend, though maximum heat indices are difficult to ascertain at this time. 12Z GFS/NAM forecast soundings both suggest surface dewpoints will mix out into the 60s along/west of a pronounced sfc trough in the lee of the Appalachians on Sat, and uncertainty persists w/regard to the evolution of convection (upstream or otherwise) and associated mid/upper level ceilings. A heat advisory will likely be needed for portions of central NC this weekend, particularly south and east of the Triangle. Mon-Thu: Near or slightly above normal temps and above normal chances for convection are expected early next week as cyclonic flow aloft strengthens over the region. Confidence in sensible weather decreases significantly by mid-week as outlined above. At this time will indicate climo temps/precip chances. -Vincent && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... As of 745 PM Thursday... 24 hour TAF period: VFR conditions under high pressure will generally persist through the TAF period. However, a brief period of sub-VFR visbys at KRWI will be possible during the pre-dawn hours of Friday, along with the potential for isolated showers/storms and accompanying sub-VFR conditions Friday afternoon at all sites. Otherwise, expect generally a light south to west-southwesterly wind with a scattered afternoon cumulus field (VFR) developing again on Friday. Outlook: Generally VFR conditions are expected Friday evening and Saturday. Scattered thunderstorms may return as early as late Saturday and Sunday, with MVFR to IFR conditions. A better chance of afternoon/evening storms are expected by early next week as a cold front moves into the area, along with morning stratus and/or fog. && .CLIMATE... RDU Records: Date | High Year | High Min Year ------------------------------------------ 20 July | 102 1942 | 76 1981 21 July | 102 2011 | 78 1932 22 July | 103 2011 | 78 2011 23 July | 105 1952 | 78 2011 24 July | 101 2011 | 79 2011 GSO Records: Date | High Year | High Min Year ------------------------------------------ 20 July | 100 1977 | 75 1986 21 July | 102 1926 | 76 2011 22 July | 101 1926 | 77 2011 23 July | 99 1952 | 78 2010 24 July | 99 1914 | 78 2010 FAY Records: Date | High Year | High Min Year ------------------------------------------- 20 July | 104 1932 | 80 1996 21 July | 105 1932 | 79 1977 22 July | 107 1932 | 79 2011 23 July | 103 2011 | 79 1998 24 July | 105 1952 | 79 1945 && Heat Advisory from noon to 8 PM EDT Friday for NCZ010-011-025>028- 040>043-075>078-084>086-088-089. && $$ SYNOPSIS...Badgett NEAR TERM...CBL SHORT TERM...CBL/Badgett LONG TERM...Vincent AVIATION...BSD/Badgett CLIMATE...RAH is the U.S. government's official web portal to all federal, state and local government web resources and services.