Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 231528 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1128 AM 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 persistance, 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 AND MONDAY NIGHT/... As of 330 AM Sunday... The upper level trough will remain over the region through Monday night, as will the surface trough. The difference will be more cloud cover expected over the region, resulting in high temps slightly lower than previous days. Highs in the low to mid 90s expected, resulting in heat indices of 95-102. Lows still expected to be in the low to mid 70s. Expect more showers and thunderstorms Monday aft/eve, better chances in the south and east, decreasing overnight. && .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/... As of 330 AM Sunday... The upper level trough will remain over the region through Monday night, as will the surface trough. The difference will be more cloud cover expected over the region, resulting in high temps slightly lower than previous days. Highs in the low to mid 90s expected, resulting in heat indices of 95-102. Lows still expected to be in the low to mid 70s. Expect more showers and thunderstorms Monday aft/eve, better chances in the south and east, decreasing overnight. && .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 /16Z SUNDAY THROUGH THURSDAY/... As of 740 AM Sunday... 24-Hour TAF period: Expect mainly VFR conditions through the TAF period. The exception will be where storms develop late this afternoon and evening. Best chances for convection and the associated increase in winds and decrease in cigs and visbys may begin around 18Z at KFAY, however the models have backed off a bit and restrict most convective activity to the NC/VA border region after 21Z. Have kept the PROB30 mention of such in at KINT, KGSO, KRDU, and KRWI for this issuance. Some low stratus may develop toward daybreak Monday, however chances and confidence in sub-vfr cigs is low at this time. Looking ahead: Mainly VFR conditions expected through Tuesday, with the primary sub-VFR risk coming courtesy of showers and storms that will grow in coverage each successive day through Tue. Chances for early morning stratus increase Wednesday through Friday, but otherwise expect VFR conditions to prevail. && .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...
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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.
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&& $$ SYNOPSIS...BLAES NEAR TERM...BLAES SHORT TERM...KCP LONG TERM...RE AVIATION...KCP CLIMATE...RAH

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