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Flash Flood Guidance
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Issued by NWS
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678 AWUS01 KWNH 072351 FFGMPD NCZ000-SCZ000-GAZ000-080530- Mesoscale Precipitation Discussion 0585 NWS Weather Prediction Center College Park MD 751 PM EDT Sun Jul 07 2024 Areas affected...Western South Carolina and Eastern Georgia Concerning...Heavy rainfall...Flash flooding likely Valid 072350Z - 080530Z SUMMARY...Storms colliding in an atmosphere with abundant moisture and instability are likely to cause flash flooding, especially in areas hard hit by storms yesterday. Locally significant flash flooding possible. DISCUSSION...Flash flooding is likely this evening across South Carolina and Georgia as 2 areas of storms...one moving north over south Georgia, and the other moving southeast over northwest South Carolina collide somewhere near the I-20 corridor. This area was hard hit with storms just yesterday, so many areas, especially in and around Augusta have yet to recover from the heavy rainfall last evening. Thus...FFGs are lower in these hard-hit areas. Further, the storms are in an environment highly favorable for efficient warm-rain processes. PWATs are between 2.3 and 2.5 inches based on SPC Mesoanalysis, and CAPE values are between 2,000 and 3,000 J/kg. These variables will help support the storms producing heavy rainfall. Rates with the storms over northwestern South Carolina have locally approached 3 inches per hour. The collision of the 2 areas of storms and their respective outflow boundaries will further enhance the lift by increasing the forcing in this area. Given inflow of additional moisture from the Atlantic, this will not only support long-lived heavy rain producing storms, but also further enhance the rates the strongest storms may achieve. Thus, rates to 4 inches per hour are possible with the strongest storms this evening. 18Z HREF neighborhood probability guidance shows a corridor of 70-80% chance of exceeding 3 inches of rain in 6 hours along the I-20 corridor from Augusta through Columbia, a 50-60% chance of exceeding 10-year ARIs in 6 hours, and a 50-60% chance of exceeding 3-hour FFGs between 00Z and 03Z. CAMs guidance over the next few hours shows the storms moving SE largely overtaking the ones moving N as they follow the instability southeastward towards the coast...but with some potential slowing of their forward speed as the outflow boundaries between the 2 sets of storms collide. Wegman ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...CAE...CHS...FFC...GSP...ILM... ATTN...RFC...SERFC...NWC... LAT...LON 34908095 34627981 33578014 32618104 32398211 32748348 34088339 34168247 34888144