Flash Flood Guidance
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Issued by NWS
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519 AWUS01 KWNH 301824 FFGMPD LAZ000-ARZ000-TXZ000-OKZ000-310015- Mesoscale Precipitation Discussion 0347 NWS Weather Prediction Center College Park MD 223 PM EDT Thu May 30 2024 Areas affected...Northeast TX...Northwest LA...Southeast OK...Ext Southwest AR... Concerning...Heavy rainfall...Flash flooding likely Valid 301820Z - 310015Z SUMMARY...Slow moving thunderstorms ahead of dual squall lines with ample deep layer moisture to support 1.5-2"/hr rates with cell mergers/repeating and short-term training elements to support spots of 3-4" in short duration maintaining likely environment for scattered flash flooding through the late afternoon/evening. DISCUSSION...GOES-E WV depicts a broad cirrus shield with excellent outflow features/transverse banding along all directions denoting the MCS lies at the apex of synoptic scale ridge. Overshooting cooling/tops break through the canopy along the leading eastern edg and southern hemisphere. Regional RADAR mosaic highlights the forcing boundaries/effective frontal features well with the decaying MCV across central OK. At the surface, the effective warm frontal zone extends from convective cluster near NOLA bisecting LA into SE OK/NE TX along the Red River. Tds south of the Red River are generally 5 degrees warmer into the low and mid-70s though a nose of enhanced upper 60s exists north into NE OK. The front intersects older outflow NW of Paris, TX with a strong 1017mb meso-high near TKI/F00, that refocuses the frontal zone near a more defined meso-low near XBI before mid-level dry air mixing is allowing the cold front to surge southeast out of Northwest TX. As such, a large area of unstable (2000-3000 J/kg) of MLCAPE exists across the area of concern with solid streamline confluence to maintain active squall-line features. Total PWats of 1.75 nearing 2" exist at the base of the old outflow boundary. Flux of 5-15kts per VWP through the boundary layer will support 2"/hr rates, perhaps slightly higher along the strongest isentropic ascent of the bow echo; though duration will likely limit overall totals. As the OK MCV has been decaying, forward propagation and larger scale flow is reducing forward motions and only the stronger dry air mixing along the SW backside of the MCV is driving faster cell motions. RADAR and GOES-Vis shows warm sector over-turning as well with scattered cells developing with higher concentration along/south of the effective warm front. This will given an opportunity for pre-soaking soils with 1-2" spots and allow for cell mergers as bow(s) reach/collide with time across NE TX into far NW LA. This will allow for spots of 3-4" and perhaps an isolated spot of 5" through the afternoon and into the evening hours resulting in scattered incidents of flash flooding. Upstream bow/meso-low will track again over areas recently flooded along and north of the DFW metro, so this area will once again but under threat of an additional 1-2" compounding flash flooding ongoing through this area as well. Southeast Oklahoma...effective occluded front/TROWAL line confluence/convergence but surface based thunderstorms (with slightly lower instability) will be very slow moving across the area with some inner updrafts/downdraft tracking more northward allowing for short-term repeating and enhanced streaks of 2-4" totals also enhancning risk for flash flooding and have drawn the MPD northward to account for this potential. Gallina ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...FWD...OUN...SHV...TSA... ATTN...RFC...ABRFC...LMRFC...WGRFC...NWC... LAT...LON 35829550 35489482 34149448 33439364 32619325 32049370 31709468 31579572 31609678 31959797 32529835 33009805 33279781 33659688 34139628 35579621