233 AWUS01 KWNH 111509 FFGMPD VAZ000-NCZ000-WVZ000-SCZ000-TNZ000-111900- Mesoscale Precipitation Discussion 0966 NWS Weather Prediction Center College Park MD 1109 AM EDT Thu Oct 11 2018 Areas affected...North Carolina, Southwest Virginia, Far SE West Virginia Concerning...Heavy rainfall...Flash flooding likely Valid 111508Z - 111900Z Summary...Flash flooding is likely today from North Carolina into Virginia, associated with heavy rainfall from Tropical Storm Michael. The greatest risk from the late morning into the early afternoon will be from western North Carolina into southwest Virginia. However, flash flooding will become possible over much of North Carolina and the southern half of Virginia during that time. Some of the flash flooding could be significant and life-threatening, particularly in areas of increasing terrain near the NC-VA border. Discussion...Flooding was ongoing in portions of the Carolinas as a result of heavy rain that has already fallen from Tropical Storm Michael. Therefore, the flash flooding threat would best be described as expanding over the next several hours into additional parts of NC and southern VA as Tropical Storm Michael continues to track northeast into North Carolina. As one would expect near the lingering core of a landfalling tropical cyclone, there is a reservoir of deep tropical moisture feeding the heavy rainfall threat. The 12Z sounding from Greensboro (GSO) had a precipitable water value of 2.45 inches, which is very nearly the highest on record at that station (dating back to 1945). Ahead of the center of Michael, the cyclonic east to southeast flow was advecting this tropical moisture plume to the northwest and impinging on the terrain of the Appalachian Mountains. This had already generated some significant rainfall amounts overnight in southwestern North Carolina, with fairly widespread 3-5 inch amounts in 12 hours. Downsloping and decreasing moisture on the back side of Michael's circulation should allow precipitation to begin to diminish in SW NC, but the heavy rain is likely to continue for another several hours in NW NC, and should become increasingly focused in SW VA into the early afternoon hours. Hi-res models are showing a very high probability of over 3 inches of rain in 6 hours from NW NC into SW VA (12Z HREF), and this would generally approach or exceed flash flood guidance in most of those areas. A marginal amount of instability (MUCAPE around 300-600 j/kg) may be sufficient for some convective banding in addition to orographic enhancement, and the combination of these factors with near record PWs means that significant, life-threatening flash flooding could occur in some of these areas with deeper inundation. Further east, closer to the track of Michael and out into the Piedmont and flatter terrain, there will be more convective instability (MUCAPE closer to 1000-1500 j/kg). Therefore, tropical rain bands may be more organized in these areas and produce higher rain rates, approaching 3 in/hr at times. However, unlike in the mountainous areas where terrain features lock the heaviest rain bands in place, the rain bands further east may be more progressive and not necessarily remain situated in the same areas for hours on end. Flash flooding is still likely in these areas given the heavy tropical rain rates, but the most notable impacts may be more scattered. Flash flooding would be most likely where tropical rain bands can intersect urban areas for at least 40-60 minutes. Lamers ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...AKQ...CAE...GSP...ILM...LWX...MHX...MRX...RAH... RLX...RNK... ATTN...RFC...LMRFC...MARFC...OHRFC...SERFC... LAT...LON 38147971 37757854 37167798 36037779 35007818 34507893 34477971 34798020 35068063 35078155 34938218 35578243 36288248 37218201 37918102