AWUS01 KWNH 201746 FFGMPD FLZ000-ALZ000-MSZ000-LAZ000-TXZ000-202330- Mesoscale Precipitation Discussion 0482 NWS Weather Prediction Center College Park MD 145 PM EDT Sat Jun 20 2026 Areas affected...Gulf Coast from Houston, TX through Mobile, AL Concerning...Heavy rainfall...Flash flooding possible Valid 201745Z - 202330Z Summary...Slow moving showers and thunderstorms will become widespread along the gulf breeze through this afternoon and evening. Rainfall rates of 2-3"/hr are likely within this convection, which through slow motions could produce 2-4" of rain atop saturated soils. Flash flooding is possible. Discussion...The regional radar mosaic this aftn shows a slow expansion of thunderstorms aligning the Gulf Coast from near Houston, TX through New Orleans, LA and towards Mobile, AL. These thunderstorms are developing along a sharpening surface trough/Gulf Breeze driving enhanced convergence to support rapid convective development. The environment across the region remains extremely favorable for heavy rainfall. PWs as measured by GPS are 2.1 to 2.3 inches, or well above the 90th percentile for the date, which is combining with MLCAPE that has steadily climbed above 2500 J/kg. This is helping to fuel the rapid expansion of convection noted in the regional radar mosaic the past few hours, and hourly rainfall within this fresh development has been measured via MRMS to be 1.00 to 1.75 inches. During the next several hours, the high-res guidance, including recent runs of the HRRR and RRFS, indicate scattered to widespread convection will repeatedly develop along this boundary as convergence continues within the robust thermodynamics. Both the HREF and REFS indicate that rainfall rates will spike above 2"/hr (30-40% chance) in the deeper convection, with short term rates above 3"/hr likely as reflected by the sub-hourly HRRR. These rates will occur within primarily pulse convection due to a lack of meaningful shear, so the duration of any individual cell will likely be limited, but regenerating and repeating rounds with storm motions expected to be just around 10 kts will result in total rainfall reaching 2-4" along this boundary. This region is extremely vulnerable to flash flooding right now due to recent heavy rain. 7-day rainfall has been generally 300-600% of normal (SW LA the exception which has been dry and likely has a lower flash flood risk) leading to 0-40cm soil moisture that is above the 95th percentile in many areas. So while the heaviest rainfall may remain scattered this aftn, the recent sensitivity of this region suggests a flash flood risk will exist through peak heating into the evening hours. Weiss ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...BMX...HGX...JAN...LCH...LIX...MOB...SHV...TAE... ATTN...RFC...ALR...FWR...ORN...NWC... LAT...LON 32408874 32308787 32028690 31688636 31348619 30978634 30468737 30178816 29908897 29698979 29719035 29739115 29739219 29619349 29299472 29329516 29629548 30129494 30789388 31459211 32218975