Flash Flood Guidance
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Issued by NWS
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049 AWUS01 KWNH 041749 FFGMPD LAZ000-TXZ000-042330- Mesoscale Precipitation Discussion 0220 NWS Weather Prediction Center College Park MD 149 PM EDT Sat May 04 2024 Areas affected...Southeast TX...Southwest LA... Concerning...Heavy rainfall...Flash flooding possible Valid 041745Z - 042330Z SUMMARY...A few scattered elevated T`storms in proximity to highly saturated soil conditions may further expand over the next few hours with spots of 1-3" by 00z, possibly resulting in new flash flooding or compounding ongoing flooded areas. DISCUSSION...Regional RADAR mosaic and GOES-E imagery suite have depicted a few bands of elevated weak/scattered convection across Southeast TX, triggering along the northeast nose of enhanced 800-700mb moisture flux and warm air advection. Model guidance suggested backed mid-level flow reducing the forcing, but VWP in the region hint that is less likely to unfold with 30-40kts of 700mb SW flow at THOU/HGX and more westerly at KLCH. Lower level/boundary flow from 850 is more oblique but with CIRA LPW noting a NW-SE gradient of enhanced SFC-700 flow, while lingering 700-500mb moisture into SW LA; conditions were well for scattered narrower updraft cells to track fairly parallel for some isolated 1-2" in Polk/Tyler counties. This is along the northeastern fringe of areas that have seen greater than 8+" in the last 72hrs but ground saturation values even into SW LA remain at 75% suggesting nearly all water is run-off. Current model and observational trends suggest an increase in higher theta-E air over the next few hours (20-22z), perhaps already just off the coastline in a possible early afternoon sea-breeze enhancement lifting northward. Higher instability with SBCAPEs to 3000 J/kg and TPW of 1.5-1.6" combined with differential heating over the flooded areas north; this may increase isentropic ascent/convergence and allow for deeper rooted convection in proximity to the ongoing convection adding the potential for 1.5-2"/hr rates, resulting in spots of additional 2-3" and spots of 4" totals over the last 3hrs + next 6hrs. There is high uncertainty to this evolution but with ongoing expanding convective activity; new areas of flash flooding is considered possible through the evening hours. Gallina ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...HGX...LCH...SHV... ATTN...RFC...LMRFC...WGRFC...NWC... LAT...LON 31249515 31199448 30829270 30089273 29809369 30089469 30589545 30989553