Scientific Forecaster Discussion

Area forecast discussion National Weather Service Greenville-Spartanburg SC 706 am EDT Monday Jun 27 2016 Synopsis... high pressure will weaken over the region and shift east before a cold front sweeps in tonight. This front will become stationary early Tuesday leading to enhanced precipitation chances. High pressure should build in from the north for the middle part of next week leading to a brief period of drying. Diurnal precipitation chances will resume through late week. && Near term /through tonight/... as of 645 am EDT monday: tweaked pops across the southwest NC mtns to reflect latest radar trends. Also adjust T/TD to better align with recent obs. Otherwise, current fcst remains on track for this update. No other changes were needed/made. As of 330 am EDT monday: a broad/elongated 500 mb anticyclone prevails across much of the southern Continental U.S. While a closed low and associated trof sweep across southern Ontario, southward over the upper Midwest states. At the surface, high pressure remains draped atop the mid Atlantic while a cold front slides into the upper MS River Valley. Pattern evolution through the near term features an associated prefrontal trof advecting east into the NC high terrain this afternoon/evening before slowly propagating into the NC/SC Piedmont as well as northeast Georgia overnight, all beneath a region of upper height falls thanks to the approaching 500 mb trof axis. The surface front itself looks to lag well behind, possibly just moving through the Ohio Valley by periods end. As for today, guidance favors increasing convection amongst a destabilizing warm sector, likely enhanced by the approaching 500 mb height falls as well as the surface trof. Early on profiles are quite dry with steep low/mid level lapse rates supporting upwards of 1.5-2k j/kg SBCAPE, however profiles moisten sharply later this afternoon into the evening as guidance favors advection of an enhanced pwat airmass into the region. Weak 500 mb flow that is increasingly parallel to the intruding surface trof is supportive of slow moving, and possibly training convection. Thus, the fcst will feature scattered/numerous showers and thunderstorms initiating over the mtns by early afternoon, spreading east into northeast Georgia and the NC/SC foothills and Piedmont through the remainder of the evening and early morning hours on Tuesday. As for the hwo, will mention possibility for localized heavy rain and or flooding as well as isolated severe chances tied to peak heating/instability with the highest chances for both residing over the NC/SC/GA high terrain. Further east into the Piedmont it looks as if initiation will be delayed past peak heating by cin associated with the departing surface ridge and the lack of a triggering mechanism, thus severe looks less likely. && Short term /Tuesday through Wednesday night/... as of 210 am monday: a prefrontal trough will stall just south and east of the County warning forecast area Tuesday as the cold front drops to near The Spine of the Appalachians. Moisture pooling along the prefrontal trough will keep the best instability and forcing over the southern and eastern County warning forecast area. Therefore...have likely pop south of I-85 with chance elsewhere. Moderate instability may result southeast of I-85 with moderate shear possible as well. Cannot rule out a severe storm, but there is some uncertainty on where the best instability and shear set up, so it is still to early to tell if severe storms will be more scattered or organized. Drier air moves in Tuesday night as the cold front moves in from the northwest keeping a diurnal trend to the convection. Highs will be near normal northern tier and below normal elsewhere. Lows will be near normal. The cold front stalls across the area Wednesday with a wave of low pressure forming along the front. Moisture, and resulting instability, will be greater south and east of the front with lower amounts to the north. There is some disagreement in the guidance on the location of the front and resulting convection. Guidance blend comes up with scattered convection from the Charlotte Metro area southwest to the lakelands, with isolated convection to the north. Highs will return to near normal levels with lows nearly steady near normal. && Long term /Thursday through Sunday/... as of 325 am sunday: guidance in good agreement aloft showing eastern trough Rocky Mountain ridge remaining in place through the period. At the surface, a frontal system remains stalled near or over the area Thursday and Friday. A cold front drops into the area Saturday and merges with the stalled front on Sunday. Moisture and instability will favor the eastern and southern portions of the County warning forecast area closer to the stalled front on Thursday and Friday. Expect mainly diurnal scattered convection there with isolated convection to the west. Precip chances increase Saturday and Sunday as the second front drops into the area with increasing moisture inflow across the area and good forcing. Expect scattered mainly diurnal convection Saturday with likely coverage mountains and good chance elsewhere on Sunday. Will have to keep an eye on the weekend systems and there could be enough forcing and shear for organized convection, and enough moisture and potentially training cells to increase the flood potential. Near normal temps Thursday will rise a little above normal for Friday and Saturday, then drop back to near normal for Sunday. && Aviation /11z Monday through Friday/... at kclt: VFR through the vast majority of the taf cycle. Surface high pressure starting its retreat to the east allowing southerly flow to initiate this morning. Sct low/mid VFR beneath high clouds will persist through the first few hours of the taf cycle before low VFR cu prevails. A prefrontal trof will move into western NC this afternoon, spreading convection east into the NC/SC Piedmont by late afternoon to early evening. Therefore taf features lowering VFR stratocu within a tsra tempo from 22-02z, ahead of a prevailing shra with a tsra prob30 through early morning. Winds through the period will remain light and southerly with gusting possible adjacent to any stronger/deeper convection. Elsewhere: trends similar to that of kclt above as it pertains to afternoon/evening convection. Current low stratus along the Blue Ridge southward into northeast Georgia and the SC upstate, will persist through much of the morning however lifting slightly within the next 2 hours. Opted to remove any fog mention from previous taf set as persistent sky cover has worked to keep TD depressions elevated. As stated above, convection will initiate this afternoon ahead of a prefrontal trof, before sweeping east over the remainder of the region this afternoon/evening. All sites feature shra/vcts and tempos for tsra with timing based upon cam consensus as well as latest NAM. Winds will remain generally light and southerly at all sites with gusting possible adjacent to deeper convection, slowly veering to the WSW late in the period. Outlook: precipitation chances will persist into Tuesday as frontal moisture remains in the vicinity leading to possible tsra related restrictions. Diurnally favored shra/tsra will return mid/late week leading to additional restrictions by way of convection and morning fog/cigs. Confidence table... 11-17z 17-23z 23-05z 05-06z kclt high 100% high 100% high 100% high 100% kgsp Med 61% high 100% high 100% high 100% kavl Med 61% high 100% high 100% Med 78% khky high 100% high 100% high 100% high 100% kgmu Med 61% high 100% high 100% high 100% kand Med 66% high 100% high 100% high 100% The percentage reflects the number of guidance members agreeing with the schedule taf issuance flight rule category. Complete hourly experimental aviation forecast consistency tables and ensemble forecasts are available at the following link: Www.Weather.Gov/gsp/aviation && Gsp watches/warnings/advisories... Georgia...none. NC...none. SC...none. && $$ Synopsis...rwh near term...cdg short term...rwh long term...rwh aviation...cdg

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