Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Sep 14 2023 08:48:31 AWUS01 KWNH 140848 FFGMPD TXZ000-141430- Mesoscale Precipitation Discussion 1069 NWS Weather Prediction Center College Park MD 447 AM EDT Thu Sep 14 2023 Areas affected...Central Texas... Concerning...Heavy rainfall...Flash flooding possible Valid 140845Z - 141430Z SUMMARY...Increasing convective converge at leading edge of enhanced low level moisture and strengthening LLJ. A potential for training will become more likely toward daybreak across central TX. Spots of 2-4" and intense short-term rain rates pose possible instances of flash flooding this morning. DISCUSSION...GOES-E 3.9um SWIR loop depicts increasing coverage of numerous low level Cu/TCu across the eastern Hill Country expanding northward across the southern Big Country into the Heart of Texas. This is in response to strengthening and slowly veering LLJ across south-central Texas starting to ascend to some weak to modest elevated conditionally unstable air across the region.=20 Along the way, as the LLJ veered from south-south east to south, a SW to NE band of enhanced 925 FGEN convergence was sufficient to spark a few isolated thunderstorms that currently scattered from Edwards/Real county toward Williamson county. CIRA LPW sfc/850mb layer denoted a very narrow but anomalously high 1.25" layer ideally intersected for increased moisture loading into stronger updrafts. One cell in particular has been a bit more prolific in W Gillispie county where convergence appeared to be maximized producing rates over 2"+/hr and likely localized totals over 3-4". A few other cells may have similar rates/totals over the next few hours before the focus/best convergence lifts northward. While prolonged moderate drought has persisted, these types of rates/totals across hardened ground surface will have very limited infiltration and increased run-off is probable, especially over the Hill country where FFG is naturally lower. Over the next few hours... A subtle/sheared shortwave is tracking through the TX panhandle and has sparked a few lines of fairly progressive thunderstorms across the Cap Rock. The wave and associated mid-level ascent pattern has aided in the strengthening and veering of the LLJ. As noted above, the source low level moisture is well above normal with an additional .75" in the 850-700mb layer; total PWats over 2" will allow for increased rainfall efficiency that will be required for increased runoff and flash flooding conditions. The limiting factor is weak to modest lapse rates only support about 500-750 J/kg of instability. Still, given the flux convergence and level of available moisture, there is solid signal to suggest 2"/hr rates are possible even in narrow up/downdraft cores. Deep layer steering from 700mb and above should allow for some potential for training/repeating, the narrow cores, may not allow for broad areas and the results may be spotty locations of 2-4" through late overnight past daybreak, with best chances further east, given deeper moisture and longer potential for repeating cells. All that stated, this still remains a not particularly confident forecast given the limited instability and Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_xQeXE_pD-efUk294uMuj1PUK_sMIN4iLXZa_FnzCgxppvAwIEVDmVsLaBRwutbwnwDt= LYPiIM4oPyELVw7QNKCF5F8$ for graphic product... ATTN...WFO...EWX...FWD...SJT... ATTN...RFC...WGRFC...NWC... LAT...LON 33039962 32949886 32419726 32009659 31519623=20 31109615 30989632 30659680 30109783 29829879=20 29989951 30659998 31699997 32109997 32780003=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) .