Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 192008 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 406 PM EDT Tue Jun 19 2018 .SYNOPSIS... A ridge of high pressure over the southeastern United States will shift south but largely persist through the work week. A cold front will drift int the region on Wednesday and linger through Thursday before lifting north late Friday. .NEAR TERM /THROUGH TONIGHT/... As of 220 PM Tuesday... ...Heat Advisory in Effect through 8 PM this evening and for 11 AM to 9 PM Wednesday for the Sandhills, the southern Coastal Plain and the eastern Piedmont... Latest surface analysis shows surface high pressure centered across the TN Valley with a surface trough extending from the DELMARVA Peninsula southwest across the eastern Piedmont of the Carolinas. In addition, a cold front was analyzed from the eastern shore of VA/MD west across VA into the OH Valley. The air mass across central NC is moderately unstable with MLCAPE values averaging between 1000 to 1500 J/Kg, perhaps a little more across the east/southeast. The atmosphere is warm today with H5 temperatures around -5C and the warm mid levels will result in meager mid-level lapse rates of around 5.5. In contrast, deep mixing has resulted in DCAPE values ranging from 1000-1300 J/kg, greatest in the east. Satellite imagery shows limited cumulus development this afternoon with the greatest coverage and depth across the Sandhills and southern Coastal Plain. The degree of convective development and more importantly, the evolution and movement of features developing outside of central NC is difficult. In general, we still expect less convective coverage than previous days as larger scale forcing mechanisms are lacking. However, isolated thunderstorms are likely to develop in the Sandhills and southern Coastal Plain, especially near the NC/SC border in a region of slightly better low-level convergence. Regional radar imagery is already showing scattered thunderstorms developing across the VA and especially NC mountains that are moving southeast in the northwest flow aloft. These storms may impact the western Piedmont later this evening. Finally, more widespread convection is likely develop across VA late this afternoon ahead of a southward advancing cold front. The convection or weakened remnants will move south and reach the northern Piedmont and Coastal Plain toward midnight and slip southeast. While the upper flow is weak and convection will likely be unorganized, there is the potential for a damaging downburst given the steep low level lapse rates and high DCAPE. While perhaps limited in coverage, some convection may still be ongoing late into the evening or early overnight hours. Lows tonight will range between 73 and 78, near record high minimums. -Blaes && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... As of 315 PM Tuesday... The upper-level ridge shifts south on Wednesday and Wednesday night resulting in falling heights across the Carolinas. As the ridge shifts south, the westerlies aloft strengthen across the area and a progressive short wave trough moves from the OH Valley into the mid-Atlantic during the afternoon and evening. In addition, the southward advancing cold front across the mid- Atlantic should have reached the northern/northeastern part of the CWA by Wednesday morning and stalled with convective outflow from tonight`s convection likely extending further southwest into the RAH CWA. Expect scattered showers and storms to develop again on Wednesday, with the greatest coverage across the northern and northeastern portion of the CWA, in proximity to the surface boundary. Stronger flow aloft will result in 0-6km shear of 20-30 kts which combined with a weak to moderately unstable air mass, could result in some storm organization in the form of some multicells and clusters and the risk of a few strong to severe storms across the northeastern counties. Low-level thicknesses and H8 temperature relax a bit on Wednesday as the ridge shifts south. Highs on Wednesday should range a couple of degrees cooler than today with highs on Wednesday in the lower 90s north to mid 90s south. Heat index values will approach criteria again on Wednesday afternoon across the southeast. Removed Halifax, Edgecombe, Nash and Franklin from the advisory tomorrow as the cooler air mass near the front should hold temps back in those area. Still muggy on Wednesday night with lows in the 72 to 77 range. -Blaes && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... As of 350 AM Tuesday... Low-level thicknesses and H8 temps begin to wane Wednesday in response to the de-amplifying and southward suppression of the the mid/upper level ridge into the Deep South/eastern GOM. Thus, highs Wednesday should average a few degrees cooler than today. Highs ranging from lower 90s north to mid 90s south. When combined with the 70 degree dewpoints, heat indices across the Sandhills and southern and central Coastal Plain counties will once again range between 103 to 107 degrees. As such, we will likely need to issue another heat advisory on Wednesday for much of the same area. Isolated to scattered diurnal convection should once again develop near the lee surface trough Wednesday afternoon. The northern/northeastern tier counties have the potential to see a period of likely pops during the late afternoon/early evening, where closer proximity to a quasi-stationary west-east frontal boundary and associated convection/outflow extending across the Mid-Atlantic region could propagate south into the area. Enhanced sheared to the north along the front, could result a few strong to severe storms across the northeastern counties. Lows Wednesday night in the lower to mid 70s. && .LONG TERM /THURSDAY THROUGH TUESDAY/... As of 400 PM Tuesday... Pattern overview: A complex mid-upr level low over the nrn/cntl Rockies will amplify sewd across the cntl Plains through Thu, then reach the mid MS Valley by 12Z Fri. Preceding, and influenced by that low, a portion of a mid level low now over srn TX will eject/shear shear newd across the TN Valley Thu, and srn and cntl Appalachians Thu night. The models indicate the parent low amplifying from the nrn Rockies to the mid MS Valley will then lift newd across the OH Valley and lwr Great Lakes on Sat, with associated glancing forcing for ascent and seasonably strong, 30-40 kts of swly mid level flow forecast Sat over cntl NC. Modest, quasi- zonal to broadly cyclonic flow aloft will then prevail across NC ahead of a strong nrn stream shortwave trough forecast to sweep off the Northeast and nrn middle Atlantic coast on Mon. Following ridging aloft is then forecast to build from the lwr MS Valley to the cntl Appalachians through the middle of the week. At the surface, the synoptic frontal zone now draped from the middle Atlantic coast wwd across the OH Valley, will settle swd and merge/overtake a preceding lee low over NC Thu, then become quasi- stationary in the vicinity of cntl/ern NC Thu night-Fri. This frontal zone will then retreat nwd once again with subsequent Appalachian-lee troughing through the weekend. A following cold front is then forecast to cross the srn middle Atlantic states on Mon, followed by high pressure that may curb the heat and humidity by Tue. But the likelihood of a front making a complete passage through NC this time of year is relatively low, as is predictability in general at Day 7. Sensible weather: Above average temperatures are most likely to be interrupted behind the aforementioned two (partial) frontal passages, on Fri and Tue. Precipitation/convective chances will also be maximized along those fronts, particularly late Thu-Fri. Environmental shear in the presence of the front Fri may also favor a semi-organized storm mode and marginal risk of severe weather during that time. Mainly diurnal convection, with slight to low chances, is otherwise anticipated throughout the period. && .AVIATION /19Z TUESDAY THROUGH SUNDAY/... As of 205 PM Tuesday... 24 Hour TAF Period: Isolated thunderstorms will develop near the NC/SC border this afternoon, potentially impacting the FAY terminal through early this evening. In addition, scattered thunderstorms developing across the NC/VA mountains may drift southeast into the northwestern and northern Piedmont later this evening. Finally, more widespread convection is likely develop across VA late this afternoon and move south with the weakening remnants pushing into the northern Piedmont and Coastal Plain after midnight with possibly VFR CIGs and a small chance of convection. Outside of these lower end possibilities, VFR conditions are expected across most of the area through the TAF period. There is a limited threat of some SCT- BKN stratus or patchy fog across the northeast toward daybreak as well. Outlook: The chances of adverse aviation conditions with scattered, mainly afternoon and evening showers and thunderstorms will increase on Wednesday through the weekend as a cold front approaches and then lingers near or just north of the region. -Blaes && .CLIMATE... Max temperature and high-minimum temperature records... GSO: REC HI DAY MAX YR MIN YR 06/19 100 1944 77 1970 06/20 100 1924 75 2009 06/21 100 1933 75 1924 06/22 100 1914 75 1981 ------------------------------------- RDU: REC HI DAY MAX YR MIN YR 06/19 102 1944 73 2010 06/20 102 1887 77 1924 06/21 101 1933 75 1933 06/22 100 1981 78 1933 ------------------------------------- FAY: REC HI DAY MAX YR MIN YR 06/19 102 1944 77 2017 06/20 102 1970 77 2009 06/21 105 1933 84 1928 06/22 101 1990 84 1928 && .RAH WATCHES/WARNINGS/ADVISORIES... Heat Advisory until 8 PM EDT this evening for NCZ010-011- 026>028-041>043-075>078-084>086-088-089. Heat Advisory from 11 AM to 8 PM EDT Wednesday for NCZ041>043- 075>078-085-086-088-089. && $$ SYNOPSIS...BLAES NEAR TERM...BLAES SHORT TERM...BLAES LONG TERM...MWS AVIATION...BLAES CLIMATE...KCP

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