Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Oct 03 2023 16:10:22 AWUS01 KWNH 031610 FFGMPD TXZ000-032208- Mesoscale Precipitation Discussion 1128 NWS Weather Prediction Center College Park MD 1209 PM EDT Tue Oct 03 2023 Areas affected...Upper TX Gulf Coast Concerning...Heavy rainfall...Flash flooding possible Valid 031608Z - 032208Z Summary...Rainfall rates as high as 1-3"/hr may support localized totals of 3-5"+ through the afternoon. Isolated instances of flash flooding are possible. Discussion...Showers and thunderstorms are ongoing along a narrow convergence axis situated across the Upper TX Gulf Coast. The mesoscale environment is characterized by increasing instability along the coast (with a sharp gradient of 500-2500 J/kg of ML CAPE), PWATs of 2.0-2.3 inches (between the 90th percentile and max moving average, per adjacent LCH sounding climatology), and effective bulk shear of 20-25 kts. SPC RAP analysis indicates strong deep moisture flux occurring across the narrow convergence axis, with modest low-level (925 mb) moisture transport from 20 kt southeasterly flow from the Gulf. Additionally, a subtle equatorward arcing subtropical jet streak (~60 kt at 250 mb) may provide some divergence aloft via the right-entrance region (though a much larger ~90 kt jet streak over southeast NM and the TX Panhandle may be mitigating the effect via its right-exit region). There is little other upper-level support to speak of (with a distinct lack of shortwaves within the larger-scale ridging). While the synoptic-scale supporting conditions for heavy rainfall are a bit murky, things appear to remain favorable on the mesoscale for continued localized heavy rainfall through the afternoon hours. The 12z HREF model suite is in fairly good agreement with depicting localized 3-5" totals through 22z (with the NAM-nest and FV3 members being particularly wet outliers depicting the potential for 6"+ localized totals). HRRR runs from 09-14z have also generally supported totals in this range, though oriented on the western side of the HREF guidance (suggesting the highest totals occur near the I-45 corridor and possibly extending inland to the Houston metro proper). Observational trends generally support the HRRR depictions, and those magnitudes also seem most likely (with the NAM-nest and FV3 probably a bit overdone). Flash Flood Guidance (FFG) generally ranges from 3-5" over a 6-hr period, but ranges from as low as 2-3" over a 1-hr period. Recent observational trends (per MRMS) have supported localized rainfall rates of 1-3"/hr, and some training/repeating is possible given that the convergence axis will shift very little through the afternoon. This puts the more vulnerable Houston metro area at risk, particularly across low-lying and poor drainage areas (should the heaviest rainfall overlap those sensitive regions). That said, relatively dry antecedent conditions (and the associated FFG) suggests that the rain should largely be beneficial, and therefore localized/isolated instances of flash flooding are considered to be possible (rather than likely). Churchill ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6gbq1kH41kL4Rlee_K4IxgFZX7gD9jQAw2Yv4v12zpLyluUuhuBh2Fw2xauRqwuHhHnW= OIu7uqQEvQDVibG9VdWFZwE$ for graphic product... ATTN...WFO...HGX...LCH... ATTN...RFC...WGRFC...NWC... LAT...LON 30749531 30509472 30109425 29659398 29219436=20 28679514 28469616 29039623 29949607 30629586=20 =20=20=20=20=20=20=20=20=20=20=20=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .