Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 201808 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 200 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/...
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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.
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&& .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 /18Z THURSDAY THROUGH TUESDAY/... 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. && .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...BLAES AVIATION...Badgett CLIMATE...RAH

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