Flash Flood Guidance
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Issued by NWS
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713 AWUS01 KWNH 121725 FFGMPD NCZ000-SCZ000-GAZ000-122330- Mesoscale Precipitation Discussion 0870 NWS Weather Prediction Center College Park MD 124 PM EDT Mon Aug 12 2024 Areas affected...Carolina Coastal Plains & Extreme E GA Coast. Concerning...Heavy rainfall...Flash flooding likely Valid 121730Z - 122330Z SUMMARY...Lingering frontal zone and Sea Breeze convection over saturated ground conditions continue to pose scattered but likely flash flooding conditions in cells capable of 2-2.5"/hr and spots of 4"+ possible. DISCUSSION...17z surface analysis denotes pesky stationary front from Cape Hatteras along the SE NC coast toward a surface wave along the SC/NC state line just ashore; the front continues west along I20 before becoming less discernible west of Athens, GA. Enhanced moisture still over mid-70s Tds exist along both sides of the boundary which using CIRA LPW extends through 700mb, before a dry slot can be analyzed across south-central GA bleeding into S Low Country of SC...however, pooling of moisture through 500mb near the front brings total PWat Values over 2-2.25". Of note, early cu along the GA/SC note, that the surface moisture into the low 80s and confluent flow will likely sharpen the sea breeze as it develops in the next few hours. Unsurprisingly, CAPE over 2500 J/kg exists in proximity of the front through central SC before increasing to over 3500 J/kg along the SC/NC coast. GOES-E WV shows polar closed low is dipping southward into the Mid-Atlantic, and the polar jet is splitting a bit under this influence. So oblique right entrance ascent is going to a favorable factor for some cell organization nearer the front but further east. Currently RADAR and GOES-E Visible note the initial developing cells in E NC, which are likely to continue to deepen and expand in coverage. Cells very near the coast may become a bit more locked to the coast given strengthening sea-breeze which seems to be a solid consensus within the Hi-Res CAMs providing increased confidence in activity. HREF probabilities of 2"/hr are fairly high with some isolated 10-15% values for 3"/hr across much of E NC decreasing in coverage along the front and down the SC coast. High 60-70% probability in neighborhood 3"/6hr and even a 30% of 5" is enough for probable flash flooding potential. However, given the grounds still remain well above average in saturation from the prolonged rainfall over the last week, incidents of flash flooding are considered likely, especially in E NC; with decreasing coverage potential into central SC and even further across central and southern coastal SC where cells are likely to be more pulse in nature given mixing of mid-level dry air (though will have intense rainfall production in that short duration). Gallina ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...CAE...CHS...ILM...MHX...RAH... ATTN...RFC...SERFC...NWC... LAT...LON 35817753 35737659 35727588 35227560 34897602 34577636 34567697 34247757 33707804 33617881 32937930 32508002 32138049 31748109 32178140 32868113 33228167 33548197 34018173 34568060 34967971 35617818