Flash Flood Guidance
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Issued by NWS
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638 AWUS01 KWNH 261506 FFGMPD SCZ000-GAZ000-262105- Mesoscale Precipitation Discussion 1067 NWS Weather Prediction Center College Park MD 1106 AM EDT Thu Sep 26 2024 Areas affected...South Carolina and Eastern Georgia Concerning...Heavy rainfall...Flash flooding likely Valid 261505Z - 262105Z SUMMARY...Extremely heavy rainfall in heavy banding will persist into the afternoon over eastern Georgia and central South Carolina including Columbia. Widespread flash flooding with locally significant impacts is likely through the mid-afternoon. DISCUSSION...Regional radar imagery at 15Z showed an axis of heavy rainfall extending north-south over southern to central SC. This band is redeveloping on the south end and shifting north, nearly along its axis causing hourly rates of 2.5"/hr. This particular band is tracking into Columbia which is rather flood prone. The axis of heavy rain has been co-located with an area of strong low level moisture flux convergence in a plume of 2.2 to 2.5" PW which is the core of moisture streaming ahead of Helene on southerly 35kt low level flow. Instability is rather limited decreasing from 1500 J/kg near the SC coast to less than 500 J/kg near Columbia, but this is overcome from strong dynamics where the mean layer southerly flow is 40kt and oriented with the activity, causing training. Recent HRRR runs are under doing this band and feature more scattered convective modes through the mid-afternoon. However, the channeling of this flow between the upper low that remains over western TN and the ridge east of FL will maintain redeveloping advection and banding ahead of Helene. Given little change in the forcing mechanisms in place, heavy rain potential will continue into the mid-afternoon across many of the same locations already seeing heavy rain. While FFG was rather elevated over these areas, it is quickly dropping as heavy rain spreads in. The extreme rates warrants likely wording for the flash flood risk. There should be some break in heavy rain here later this afternoon before banding from Helene returns this evening as the system passes to the west. Jackson ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...CAE...CHS...FFC...GSP...ILM...JAX... ATTN...RFC...SERFC...NWC... LAT...LON 35078146 34428010 33737988 32777985 32068065 31248119 31618254 32388283 32908317 33288314 33428275 33828248 34488209 35048177