Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Mar 16 2024 02:02:40 AWUS01 KWNH 160202 FFGMPD TXZ000-160730- Mesoscale Precipitation Discussion 0103 NWS Weather Prediction Center College Park MD 1002 PM EDT Fri Mar 15 2024 Areas affected...Lower Rio Grande Valley of Texas... Concerning...Heavy rainfall...Flash flooding possible Valid 160200Z - 160730Z SUMMARY...Broad downdraft supercells with large hail and intense rainfall rates to cross the Rio Grande with left-splits and upscale development into a broader complex into the overnight period. Highly focused and slow cell motions may result in 2-3"/hr totals and possible flash flooding. DISCUSSION...GOES-E and regional RADAR mosaic denotes a pair of broad updraft supercells along the Mexican side of the Rio Grande continuing to translate slowly along the instability axis. Slow southward sagging cold front is aiding moisture flux convergence into the theta-E axis that is banked up along the Sierra Madre Oriental/Serranias del Burro, with Tds of low to mid-70s and return southeasterly flow parallel to the axis along the Rio Grande at 20-25kts resulting in total PWats of 1.25 to 1.6 from south to north. Elevated mixed layer at 700-500mb from the south-southwest has allowed for very steep lapse rates and therefore continued very high instability of 2500-3500 J/kg of CAPE for cells to utilize. While this profile provides for hail production, the ample deeper layer moisture (generally up to 800mb) and solid flux will allow for accompanying intense rainfall production as well with 2-3"/hr rates possible. The uncertainty resides in a couple of factors; (1) Duration, though broad updrafts and slow right moving cell motions may allow for 30-45 minutes of intense rainfall production overall totals may still be a the lower threshold of the higher capacity soil conditions in the region per FFG values of 3"/hr and 4"+/3hr. (2) Location, current trends are for continued strong easterly flow through the theta-E axis into the upslope region of the Sierra Madre keeping upstream redevelopment along the terrain and with deep layer effective bulk shear over 60kts...cells are more likely to turn right along the axis resulting in training more so on the Mexico side of the boarder. However, left splitting updrafts are likely throughout the cycle and likely limited in duration moving away from the best moisture flux, still may remain potent enough.=20 (3) Upscale growth, while models are less aggressive on this scenario, there are suggestions in the WV/EIR loops and RADAR mosaic for development to be filling in allowing for a larger mesoscale complex to develop over the next few hours. The RAP hints as some increased divergence along the lower Rio Grande in the next few hours with shortwave ridging developing. This may be manifest out of the strength of the updrafts and mesoscale outflow jet or some combination with the upper-jet/closed orientation to the NW across S NM/W TX. Either way, any upscale growth would favor an eastward migration resulting in intense rates into South Texas. Bottom line, strong cells with rainfall intensity to rapidly overwhelm even dry soils may result in rapid runoff and possible flash flooding in and around the Rio Grande Valley through the early overnight period with low confidence in precise placement. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5QJNDWrfWwwlzhixlkHFzfr8EJLi8lfMnR5ZuKpCaAT9w4Wg8JtHV4hTMSXK6ERXjjdZ= zESRuUoezKW7pQbF2pgFvjs$ for graphic product... ATTN...WFO...BRO...CRP... ATTN...RFC...WGRFC...NWC... LAT...LON 28169931 27969888 27519846 26629816 26099788=20 26039833 26389913 26869945 27309960 27649980=20 27869998 28030005 28119992=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .