Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 211503 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1100 AM EDT Fri Jul 21 2017 .SYNOPSIS...
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A hot upper level high pressure will remain in place from the Plains eastward over our region into the weekend. A cold front will approach from the northwest late in the weekend into early next week as the high pressure breaks down over the region.
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&& .NEAR TERM /THIS AFTERNOON THROUGH TONIGHT/...
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As of 1100 AM Friday... Heat advisory in effect for much of the eastern Piedmont, Sandhills, and Coastal Plain for heat indices of 105+ this afternoon. A chance of a few strong thunderstorms this afternoon at 20-30 percent. Temperatures were already at or approaching 90 for much of the Heat Advisory area, with the "cooler" NW Piedmont zones not really that far behind in the heat. Satellite data indicated some cumulus along the Piedmont trough and over the Blue Ridge. Otherwise, strong heating with sunny skies noted. Dew points were slowly mixing out from the 70s into the upper 60s in the rear of the Piedmont trough over the Triad, with "outrageous" dew points down east (81 at Goldsboro, 77 at Fayetteville, 77 at Smithfield etc.. Highs are expected to reach 95-99 this afternoon, with 100 around Fayetteville. Heat indices will approach 110 in the FAY and GSB areas. An Excessive Heat Warning may be needed later today if lows are still anticipated to remain 77+ overnight - with heat indices of near 110 again Saturday in these areas. The latest data analysis indicated a well defined surface trough stretching SW to NE across the Piedmont, or roughly from near Charlotte to Raleigh. It is along this boundary were isolated thunderstorms are favored to develop this afternoon. MLCapes of 2000+ J/KG and high freezing levels support mainly a gusty wind threat with any storm. Even within this favored zone near the trough, POP is no higher than 20-30 percent for any one given spot for a thunderstorm. The MCS tracking toward the central Appalachians from Ohio is expected to track ESE over WVA and western VA this afternoon. There is a potential for outflow from this feature to help initiate or even enhance the chance of diurnally driven thunderstorms over SW VA and possibly NW NC Mountains this afternoon. Some of the CAMS indicate the probability (30-40 percent) that the NW Piedmont may get in to some action by mid to late day. We are not currently in any outlook by SPC; however, any storms that form or move into the NW have the chance to be locally strong to severe given the available energy to work with. Convection chances are expected to drop off by mid-evening, but we will have to watch the development of upstream MCS activity later tonight. Lows will be in the 70s (80 around KFAY).
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&& .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... As of 415 AM Friday... Mid level ridging begins to flatten on Saturday as a short wave and associated front drops out of the Ohio Valley and grazes the area Saturday night. Very warm airmass in place Saturday modifies further, with low level thicknesses inching up to near 1450M (a modest 4M warmer than today = perhaps a degree warmer), so will basically maintain persistence highs from 97-99 and anticipate our heat advisory expanded perhaps a county to the west. The front will be moving across the area late in the day, and will have 30% PoPs across the northern tier from mid afternoon through midnight, with potential for showers and isolated storms to persist overnight due to outflow propagation. Persistence mins in the mid 70s Saturday night. && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 400 AM Friday... A pair of sub-tropical ridges will initially be centered over TN/KY and the west-central N. Atlantic (just se of Bermuda), with an intervening weakness/break in the ridge over the Carolinas. Both ridges are forecast to weaken through early next week, at the base of a nrn stream trough forecast to migrate across the Great Lakes and Northeast. Central NC will consequently become increasingly susceptible to passing perturbations, some resulting from upstream convection, in wly to nwly flow. At the surface, a trough will remain anchored in the lee of the srn and central Appalachians through until a synoptic cold front, one related to the aforementioned passing nrn stream trough, settles south into the Carolinas late Tue-Wed, where it will likely stall and become increasingly diffuse through Thu. The weakening and suppression of the sub-tropical ridge will result in both a gradual waning of the very hot conditions that will encompass central NC for the next few days, and also an increase in diurnally-maximized convection Sun-Tue. If medium range guidance solutions prove correct, the aforementioned frontal zone may settle far enough swwd to yield dry and near, to even slightly below average temperatures, by the middle of next week over all but the far srn tier of central NC counties/in the vicinity of the frontal zone. however, such an aggressive surge of the front to near the NC/SC line during the hottest time of year would be a somewhat atypical feat. While a Heat Advisory will probably be needed for at least a portion of central NC again Sun (Ie. the srn and ern piedmont, Sandhills, and Coastal Plain), the models indicate a good chance for the arrival of considerable high level moisture that may keep temperatures from reaching full heating potential that would otherwise favor 95 to 100 degree temperatures once again. Thereafter, increasing clouds, convective coverage, and steadily decreasing influence of the sub-tropical ridge, should collectively favor a continued downward trend into the upper 80s by the middle of next week. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... As of 645 AM Friday... 24 hour TAF period: VFR conditions under high pressure will persist through the TAF period. Isolated convection will be possible this afternoon into evening...too random to include in the TAFs. The exception could be a few showers and storms expected to develop over the eastern slopes of the northern mountains which could drift east into the Triad (INT/GSO) towards sunset...23-02Z. Winds will be light southwest. Outlook: Generally VFR conditions are expected Saturday. Scattered mainly diurnally driven convection is possible 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 ------------------------------------------ 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 ------------------------------------------ 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 ------------------------------------------- 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...Badgett SHORT TERM...mlm LONG TERM...MWS AVIATION...mlm CLIMATE...RAH

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