Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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886 FXUS62 KRAH 201856 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 256 PM EDT Thu Jul 20 2017 .SYNOPSIS... A weak upper level low off the southeast coast will drift slowly south as an upper ridge builds east over the region through Saturday. A cold front will approach late in the weekend and early next week. && .NEAR TERM /THROUGH TONIGHT/...
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As of 200 PM Thursday... The temperatures at late morning were already approaching 90. Dew points were running high, in the lower to mid 70s. The skies were sunny with the exception of some thin cirrus over VA into northern NC. These cirrus will not be thick enough to hold the temperatures back this afternoon, and with only a few cumulus we expect highs solidly into the 90s. The big question may very well be how much the low level moisture will mix out. If the dew points remain 70+, then heat indices will approach or exceed 105 in the south and east. Given that most guidance indicates that there will be enough mixing that the dew points fall back 3-5 degrees from the current readings during peak heating, we will hold off on an advisory for this afternoon Most areas will see heat indices of 98 to 104. Tonight... Only a few cirrus expected overnight with lows 70-75, except upper 60s over the rural northern Piedmont.
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&& .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... As of 200 PM Thursday... 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/...
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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
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&& .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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As of 145 PM Thursday... 24 hour TAF period, VFR conditions under high pressure will persist through the TAF period. Outlook for Friday through Tuesday, generally VFR conditions are expected Friday and Saturday. Scattered thunderstorms may return as early as late Saturday into the weekend with MVFR to IFR conditions.
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&& .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 && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Badgett NEAR TERM...Badgett SHORT TERM...Badgett LONG TERM...Vincent AVIATION...Badgett CLIMATE...RAH

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