Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 221613 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1159 AM EDT Sat Jul 22 2017 .SYNOPSIS... Hot and mainly dry sub-tropical high pressure will expand across the mid-South and southern Appalachians through the weekend, then gradually weaken by early next week. && .NEAR TERM /THROUGH TONIGHT/...
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As of 1159 AM Saturday... ...Dangerously hot conditions will expand across central NC today... Excessive Heat Warning now in effect for the cities of Raleigh and Fayetteville (counties of Wake and Cumberland) from 11 AM until 7 PM today... Heat advisory in effect for the rest of our region, including all of the Piedmont, Sandhills, and Coastal Plain from 11 AM Saturday through 7 PM today. Excessive Heat Watch remains in effect for the cities of Raleigh and Fayetteville (counties of Wake and Cumberland) from 7 PM this evening through 7 PM Sunday. The late morning surface temperatures were already in the upper 80s to lower 90s. The dew points were in the mid to upper 70s, even in the climatological drier NW Piedmont and Foothills. The surface trough was located near the Blue Ridge today, with much higher dew points and PW`s today than 24 hours ago. These readings yielded heat indices of 107 at FAY and 103 at Raleigh at 11 am. Even at Greensboro the heat index was 99 at 11 am. No changes to the current Warnings/Watches and Advisories on the heat needed as highs are still expected to reach the mid to upper 90s throughout our region, with 100 at Fayetteville. The well advertised heat indices will reach 110-115 in Raleigh and Fayetteville, and 105+ elsewhere. Satellite data indicated scattered cumulus developing over the Mountains, along the surface trough in NW NC, and along the sea breeze convergence along the SE NC beaches. A 20 POP of thunderstorms seems reasonable at any one spot this afternoon. MLCapes of 2000+ J/KG along with PW`s in excess of 2+ inches in the east suggest any storm will be capable of very heavy rain and strong, gusty wind to 45-50 mph. In addition, some CAMS models suggest that outflows from upstream convection may generate thunderstorms over northern NC this evening. This will be assessed this afternoon. Otherwise, it will be warm and sticky tonight with lows 75-80.
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&& .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... As of 415 AM Saturday... Excessive Heat Watch remains in effect for the cities of Raleigh and Fayetteville (counties of Wake and Cumberland) from through 7 PM Sunday. Generally persistence, though with a higher probability of afternoon convection, as heights aloft fall over the srn Middle Atlantic states and NC consequently becomes increasingly susceptible to passing perturbations, some resulting from upstream convection, in wly to nwly flow. Another Heat Advisory will likely be needed for all of central NC, with a good chance of another Excessive Heat Warning over at least Wake and Cumberland counties once again. The coverage and initiation time of convection, and preceding high level "blowoff" cloudiness from upstream convection, may result in slightly lower high temperatures and associated heat index values, however, but the overall cumulative affects of the heat will persist regardless. && .LONG TERM /MONDAY THROUGH FRIDAY/... As of 335 AM Saturday... A weak but fairly progressive upper level trough will move over the area on Monday and then continue eastward, taking a surface low off of the Long Island coast and out to sea. Behind the exiting low, a high pressure system will move over the northeastern CONUS that will eventually drop a cold front through the area and bring some relief to the heat. A general cooling trend will begin on Monday with temperatures easing back into the lower 90s, but dropping further into the mid to upper 80s by Wednesday afternoon, after the passage of the front. Upper 80s to low 90s will prevail through the remainder of the forecast period. The Piedmont trough and a lingering frontal boundary across the southern part of the area will be the focus for convection for much of the work week as a series of disturbances tracks along this boundary. The strongest of these disturbances could come on Tuesday night into early Wednesday morning but will be short lived before either weakening or moving out to sea. Otherwise expect diurnal showers and thunderstorms. The best chance for severe weather may be across the north on Monday as the upper dynamics are more favorable for supporting severe thunderstorms. As such the SPC has included northern portions of the CWA in a marginal to slight risk of severe thunderstorms. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... As of 745 AM Saturday... Aside from a small chance of showers and storms, and associated gusty winds and brief sub-VFR conditions, VFR conditions with a mainly light, 7-13 kt surface wind, are expected through the TAF period. The relative highest probability of convection will be at INT and GSO, where upstream convection and associated outflow, from a couple of MCS`s over the OH Valley and/or from the Appalachians, may propagate late this afternoon and this evening. Otherwise and elsewhere, an isolated "pop-up" storm will be possible, but predictability and timing of any such occurrence is too low to include for any other TAF site at this time. Outlook: Mainly VFR conditions will continue through the middle of next week, with the primary sub-VFR risk coming courtesy of showers and storms that will grow in coverage each successive day through Tue. && .CLIMATE... RDU Records: Date | High Year | High Min Year ------------------------------------------ 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 ------------------------------------------ 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 ------------------------------------------- 22 July | 107 1932 | 79 2011 23 July | 103 2011 | 79 1998 24 July | 105 1952 | 79 1945 && .RAH WATCHES/WARNINGS/ADVISORIES... Heat Advisory from 11 AM this morning to 7 PM EDT this evening for NCZ007>011-021>028-038>040-042-043-073>078-083>086-089. Excessive Heat Warning from 11 AM this morning to 7 PM EDT this evening for NCZ041-088. Excessive Heat Watch from this evening through Sunday evening for NCZ041-088. && $$ SYNOPSIS...MWS NEAR TERM...Badgett/MWS SHORT TERM...MWS LONG TERM...RE AVIATION...MWS CLIMATE...RAH

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