Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jul 12 2024 20:40:14 AWUS01 KWNH 122040 FFGMPD VAZ000-NCZ000-SCZ000-130230- Mesoscale Precipitation Discussion 0613 NWS Weather Prediction Center College Park MD 438 PM EDT Fri Jul 12 2024 Areas affected...Piedmont and Coastal Plain of Virginia, North Carolina and Northeast South Carolina... Concerning...Heavy rainfall...Flash flooding possible Valid 122040Z - 130230Z SUMMARY...Reducing coverage and longevity is expected given weakening convergence/instability parameters. However, remaining pockets of unstable air within a highly saturated environment will continue to produce scattered intense rain showers capable of inducing flash flooding given rates of 2-3"/hr, resulting in spots of 2-4" totals in short-duration (<3hrs). Scattered incidents of flash flooding remain likely through evening.=20 DISCUSSION...An extremely amplified or nearly laminar flow regime continues to hug the Carolina coast into the northeast. Favorable jet divergence is starting to wane as polar jet lifts further away across the Great Lakes while southerly branch off the coast continues to weaken in favor of return flow around the larger sub-tropical high out near 70W. As such, the trapped mid-level shortwave in coastal South Carolina continues to shear/elongate through the I-95 corridor; while the associated 850-700 wave retrograded toward near Charlotte and is lifting northward at the tail end of the favored jet divergence pattern. This has driven the 850 front further west and breaks in the cirrus deck, allowed for filtered insolation. Deeper moisture to the west and ample low level moisture in place made for very unstable airmass to develop. Low level flow backed and fluxed the higher moisture into the 850-700mb frontal/deformation zone and thunderstorms have subsequently developed. Deep layer flow is weak or slightly northeast and so cells near the Fall Line have become capable of 2-3"/hr with similar scattered totals. This will continue to expand northward into central VA; but is likely to diminish into late evening as temperatures fall with loss of insolation, though surge of moisture/convergence (as seen by arched band of convection across south central to Middle Neck of VA) may allow for some lingering organization after 00z. Across Coastal Carolinas... A short respite in activity has occurred along/east of the frontal zone from Florence, SC up along I-95 toward northeast NC. As the 850-700mb wave continues to lift northeastward with the upper-level forcing, the onshore flow has continued and will be strengthening back to 20-25kts at 850mb. This is recharging the environment of E NC, where there is some increasing temperature/dewpoint spread and therefore increasing CAPE.=20 Current activity to the west is probable to enhance low level eastward outflow and further sharpen the surface boundary. This will increase convective activity though the evening and with some speed convergence (25kts reducing to 15kts) and some isentropic ascent, should result in increasing convective activity and coverage. Total moisture values of 2.25-2.5" with 25kts of flux will allow for highly efficient rainfall production with rates of 2-3"/hr at times. However, stronger inflow will allow for a slow eastward propagation into higher unstable environment, so coverage/potential for mergers will increase. Additionally, south to north cell motions will further the potential for some localized training. As such, pockets of 2-4" totals through 03z are becoming more likely. HRRR and recent WoFS output show similar evolution and output providing some increased confidence toward these totals, including WoFS suggesting 6" totals are not completely out of the picture in NE NC, given 90th percentile output (50th is about 3.25"). All in all, this is likely to produce localized pockets of flash flooding through the early overnight hours. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_SOKFOcwosFsMiwmMi6CtEm5kUdQnLa32Norj-ilFP6kjnfor8GEhrqb8xOxloAW3FGf= 1R9OGqpYjyzullZlO7QTyoU$ for graphic product... ATTN...WFO...AKQ...CAE...GSP...ILM...LWX...MHX...RAH...RNK... ATTN...RFC...MARFC...SERFC...NWC... LAT...LON 38627767 38347731 37917627 37177623 36757602=20 35657632 34767709 33987827 33827892 33807992=20 34178055 35058069 35778044 36737996 38057907=20 38597821=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .