Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 201447 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1041 AM 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 1041 AM 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.
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&& .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... As of 345 AM Thursday... The upper level pattern on Friday is headlined by a 10-20m increase in 500 hPa heights as the upper low moves south and southwest as ridging across the Missouri Valley extends east and bridges with the subtropical ridge off the Southeast coast. At the surface a Piedmont trough will develop across VA and the Carolinas while the Bermuda high is present off the Southeast coast. Deep layer moisture will be on the increase with precipitable water values ranging between 1.75 and 2.0 inches by Friday evening. Expect only isolated to widely scattered convection to develop on Friday afternoon with convection favored to develop near the Piedmont trough, near a potential sea breeze, and especially across the higher terrain. Given the weak flow, convection will likely just drift southeast, so the terrain induced convection across the west will pose a limited threat for the western Piedmont. It will be hot Friday afternoon with guidance in good agreement... RDU statistical guidance from the GFS/NAM/EC gives highs of 97/98/99. Will forecast highs in the 95 to 99 range across central NC which is about 7-10 degrees above normal but below the record highs noted below. Heat index values will peak between 100 and 105F which is close to the Heat Advisory criteria of 105-109F for two or more hours. -Blaes && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... ...Hottest temperatures of the year so far expected over the weekend... A west-east oriented upper level ridge will build east into the region extend to the subtropical ridge off the Southeast on Saturday with 500 hPa heights across central NC reaching around 593dm. Heights drop on Sunday as the ridge breaks down and shifts south into Florida allowing the westerlies to sink into the Mid Atlantic. An increasing cyclonic flow aloft develops across the eastern CONUS on Monday as an eastern U.S. trough develops and extends south along the East Coast by Wednesday. Saturday and Sunday will be hot with highs in the middle to upper 90s across most locations with a few spots reaching 100F. Saturday will likely be the hottest day of the two with morning low level thickness values exceeding 1430m across much of central NC on Saturday morning before heights and thickness values relax slightly on Sunday. Statistical guidance for RDU from the GFS/EC gives highs of 98/98 on Saturday and 98/96 on Sunday. Heat index values will exceed 105F Saturday and Sunday across parts of central North Carolina, primarily from U.S. Route 1 south and east south/east. Heat advisories may be needed for portions of the area on Saturday and Sunday. Widely scattered afternoon and evening convection is apt to develop on Saturday, but it should be limited with 500 hPa temperatures a very mild -3 to -4C. Falling heights and steeper mid level lapse rates should support better convective coverage on Sunday. Monday through Wednesday should feature a gradual cooling trend and increase in rain chances as the eastern U.S. upper-level trough amplifies and shifts southeast with an associated cold front dropping into the Carolinas. The latest runs of the GFS and EC suggest the cold front will push further southeast, perhaps reaching the North Carolina coast by Wednesday afternoon. Its fool hardy to be confident that a cold front will be able to push through central NC and reach the coast after a hot period and more importantly on day 7 of the forecast cycle. Still, the broader pattern suggests that the front will make it into the region and support the theme of a trend toward cooler and wetter conditions. Highs on Monday will range in the lower to mid 90s, the lower 90s on Tuesday and seasonable readings in the upper 80s to lower 90s on Wednesday. -Blaes && .AVIATION /12Z THURSDAY THROUGH MONDAY/... As of 650 AM Thursday... 24 hour TAF period...VFR conditions will persist through the TAF period due to subsidence in the wake of the broad upper low/trough moving off the SE coast. Winds will be light and generally west to southwest with lee troffing over the western Piedmont through the period. Outlook for Friday through Monday...VFR conditions are expected Friday and Saturday. Scattered late day thunderstorms may return Sunday and Monday with associated MVFR to brief IFR conditions. && .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/MLM NEAR TERM...Badgett/MLM SHORT TERM...BLAES LONG TERM...BLAES AVIATION...MLM CLIMATE...RAH

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