Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 231802 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 202 PM EDT Sun Jul 23 2017 .SYNOPSIS... A Piedmont trough will extend from Virginia into South Carolina through Tuesday. A cold front will drop south into North Carolina on Tuesday and then stall across the region on Wednesday and Thursday. && .NEAR TERM /THROUGH TONIGHT/...
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As of 1100 AM Sunday... Dangerously hot conditions will continue across central NC through this evening... Difficult forecast concerning the convective initiation and development this afternoon and tonight... The latest surface analysis shows a Piedmont trough extending southwest across western VA into the western Carolinas. A southwesterly flow at the surface is present across much of central NC with surface dewpoints in the mid 70s and temperatures already in the mid to upper 80s at 10am. Further aloft, the subtropical ridge is well established across the subtropical Atlantic with other ridging across the western US with troughiness in place across Great Lakes and Mid Atlantic. A notable short wave trough will drop across the western Great Lakes this afternoon into the western OH Valley this evening. As noted above, the convective forecast for today is difficult. The air mass across central NC is generally moderately unstable with current MLCAPE values ranging from 1000-2000 J/Kg. A shallow inversion is resulting in some CIN but this will be blown away when the convective temp of 93 to 96 is reached. MLCAPE values will likely climb to between 1500 and 3000 this afternoon, fueled by slow to mix out dew points in the lower to mid 70s. Instability somewhat inhibited by warm mid levels with 500 hPa temps of -6 t0 -7 deg. But still, there`s plenty of juice out there. Scattered showers across the Southern Coastal Plain have largely fizzled out and convection that moved across southern VA and eastern TN has failed to initiate any subsequent convection at this point but the placement of an outflow boundary on the edge of a differential heating axis would suggest convective redevelopment is possible. Guidance from various convection allowing models are all over the place with the 3 or 4 most recent runs of the HRRR bouncing all over the place. In general they suggest that convection is apt to move southeast out of the mountains early this afternoon and move into NW Piedmont and VA border counties and then shift southeast across central NC this afternoon and early evening. Another band of convection/MCS may develop ahead of the OH Valley shortwave which could move into the area from the northwest around and after midnight. Much lower confidence on how that will play out given all of the features that will evolve ahead of it but it`s one to watch. The latest SPC outlook has expanded the slight risk slightly into northern NC. Main risk today will be damaging downburst winds given the profile and DCAPE values of 1200 J/kg and dangerous lightning given the abundant CAPE and higher values of NCAPE and CAPE in the -10 to -30C layer. Low-level thickness values at KGSO are similar or just a bit warmer than yesterday at this time, thickness values are 1m greater at KGSO, 8m greater at KRNK and 3m greater at KMHX. Recent visible satellite imagery shows a band of clouds across the southern Coastal Plain associated with a low-level convergence axis, most clearly noted at 925 hPa, and larger area of mainly debris clouds across the northern Piedmont, especially near the VA border. Otherwise, there`s a good deal of insolation through the haze ongoing across the area but a tendency for there to be bit more cloudiness than yesterday. See no reason to alter the current forecast highs in the 95-100 range which is supported by persistence, guidance and the morning thickness values. The convective evolution today certainly will have an impact on highs but given lower confidence on how things will shake out, will leave the temperature forecast largely as is. The combination of heat and humidity will result in heat index values from around 100 to 105 in the Triad to 107-112 across the southeast. Lows tonight will range from 73 in the Triad to 80 near Fayetteville. -Blaes
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&& .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
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As of 145 PM Sunday... Broad cyclonic flow will persist across the Mid Atlantic and Northeast on Monday and Monday night. The upper-level trough axis will shift east during the period, allowing a weak surface cold front to move into central NC Monday night and then stall. Heights at 500 hPa actually increase a bit but widespread moisture should result in a fair amount of cloudiness, especially in the mid and high levels. Depending on how convection evolves late tonight, some widely scattered showers and storms may be ongoing on Monday morning, especially across the south and east. Additional, mainly scattered storms are apt to redevelop during the midday and especially afternoon hours with the greatest coverage across the southern and eastern Piedmont and in the Coastal Plain. More limited coverage is expected across the western Piedmont and Triad. Central NC is outlooked in the general thunder category by SPC. While no organized convection is expected, can`t rule out a stronger storm given the higher CAPE and slightly stronger flow. Low-level thickness values drop about 7 to 10m across the area compared to today which combined with the cloud cover should result in highs about 2 to 4 degrees cooler than today but a few degrees warmer than previously forecast for Monday. This should result in highs in the 93 to 98 range, providing heat index values of 97-104, close but not reaching criteria, except in an isolated spot of two. For now, plan to hold off on any heat advisories and have coordinated with most of our neighboring WFOs, but we will be close to the threshold and given the multiple days of of heat issues already experienced, the mid shift will need to consider issuing an advisory. It will remain muggy on Monday night with lows in the 73 to 78 range. -Blaes
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 310 AM SUNDAY... On Tuesday the upper trough begins to lift out to the northeast as surface high pressure resides over the great lakes. The residual frontal boundary will still remain over the southern part of the state and the Piedmont trough will remain active through the week as diurnal showers and thunderstorms will be prevalent through much if not all of the period. Several weak disturbances will periodically propagate along the frontal boundary providing some extra forcing for ascent. The most notable of these will be Tuesday night into Wednesday which could increase chances for rain overnight. Late in the week a second frontal system will push down from the northwest and will affect the area by next weekend. Expect high temperatures in the upper 80s to lower 90s with lows in the low 70s. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/...
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As of 200 PM Sunday... 24-Hour TAF period...Outside of scattered convection across the area, expect mainly VFR conditions through the TAF period across central NC. Scattered thunderstorms are apt to initially develop in an arc from near Roanoke Rapid southwest to just south of Raleigh to near Lexington and then shift south and east during the mid and late afternoon hours. Additional convection may move southeast across central NC later this evening or overnight resulting from storms that may develop across the higher elevations or possibly triggered by a short wave moving into the OH Valley. Given limited thunderstorm coverage now and uncertainty about storms later this evening, we`ve omitted the inclusion of TSRA from the TAFs and just used higher end SHRA. A southwesterly flow generally around 5 to 10 kts with occasional gusts to 14 to 18kts this afternoon will relax this evening. Looking ahead... Mainly VFR conditions expected through the work week with scattered mainly afternoon and evening showers and thunderstorms. This could result in some restrictions in morning fog/stratus or storms with the greatest risk late in the work week. -Blaes
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&& .CLIMATE... RDU Records: Date | High Year | High Min Year ------------------------------------------ 23 July | 105 1952 | 78 2011 24 July | 101 2011 | 79 2011 GSO Records: Date | High Year | High Min Year ------------------------------------------ 23 July | 99 1952 | 78 2010 24 July | 99 1914 | 78 2010 FAY Records: Date | High Year | High Min Year ------------------------------------------- 23 July | 103 2011 | 79 1998 24 July | 105 1952 | 79 1945 && .RAH WATCHES/WARNINGS/ADVISORIES... Excessive Heat Warning until 7 PM EDT this evening for NCZ010- 011-026>028-041>043-077-078-085-086-088-089. Heat Advisory until 7 PM EDT this evening for NCZ007>009- 021>025-038>040-073>076-083-084. && $$ SYNOPSIS...BLAES NEAR TERM...BLAES SHORT TERM...KCP LONG TERM...RE AVIATION...BLAES CLIMATE...

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