Flash Flood Guidance
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Issued by NWS
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957 AWUS01 KWNH 092325 FFGMPD ALZ000-MSZ000-100430- Mesoscale Precipitation Discussion 0252 NWS Weather Prediction Center College Park MD 725 PM EDT Thu May 09 2024 Areas affected...Central Alabama...Eastern Mississippi... Concerning...Heavy rainfall...Flash flooding possible Valid 092325Z - 100430Z SUMMARY...Initially slow moving, intense thunderstorms to become more numerous with potential collisions and mergers after dark. Widely scattered incidents of flash flooding will become possible through late evening into early overnight. DISCUSSION...GOES-E Visible imagery aids in boundary detection with old outflow boundary angled from the FL/GA/AL corner northeast to near Birmingham before starting to meld/intersect with the trailing edge of the northern stream cold front before it flattens east to west from K1M4 into northern MS. Additionally, milky appearance and some increased congestus denotes a west to east boundary that looks to be something the emanated from the Gulf this morning. There appears to be a discontinuity in the moisture/theta-E field in the lowest levels but not enough to be remarkable. Still between these boundaries, full sun and Tds in the mid-70s has resulted in ample unstable if capped environment. However, GOES-WV and AMV along with RAP analysis fields denotes the approach of a mid-level lull in flow with subtle diffluence and speed divergence to locally enhanced mid-level cloudiness along the leading edge of 700-500mb moisture. The combination is resulting in scattered destabilization with best cells initially near BMX and low-level flow converge in the outflow boundary (nearly perpendicular as well with favorable westward curvature). Additional cells are breaking out across E MS. Total moisture to 1.75" and strong updrafts to support moisture flux into the column should support robust rainfall rates of 1-1.5"/hr probable. Quick cell motions may result in reduced rainfall totals, especially upstream with development over central MS into E MS, but in proximity to the outflow boundary, cells are likely to cluster/slow trying to anchor to the boundary much like the rotating cell in Shelby county. This will increase duration as well a potential mergers, resulting in short-term increase up to 2". Hydrologically, west-central AL/eastern MS has been fairly dry, but eastern AL remains fairly wet; especially with this morning`s heavy rainfall in the eastern quarter. MPD area aligns with 1-3hr FFG values of <2.5 and <3.5 respectively; where rain-rates/totals could be 1.5-2" and 2-3". Coverage of heavy rainfall is likely to be widely scattered with local focus where cells remain stationary or have upstream flanking line redevelopment that favors 1-2 hour repeating/training potential. Still the risk for flash flooding is non-zero and is considered possible locally within the area of concern through the early overnight period. Gallina ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...BMX...JAN... ATTN...RFC...LMRFC...SERFC...NWC... LAT...LON 33848712 33668600 32918546 32518527 32238577 32828687 32748890 33178923 33518891 33698817