Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jan 28 2023 19:20:44 FOUS30 KWBC 281920 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 219 PM EST Sat Jan 28 2023 Day 1 Valid 16Z Sat Jan 28 2023 - 12Z Sun Jan 29 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Per collaboration with WFOs HGX, LCH, and SHV, have opted to remove the Marginal Risk that was in place across the Upper TX Coast-Eastern TX into western and northern LA. Guidance trends, including the 12Z CAMs, have really backed off on the timing of the more organized convection (and setup more favorable for training) along/hear the Gulf Coast, i.e. mainly after 12Z. 12Z HREF exceedance probabilities have followed suit as well, with probs of >1"/hr rates no higher than 30-35% through 12Z Sun (where current 01 hr FFG is >2"/hr). Hurley =20 Day 2 Valid 12Z Sun Jan 29 2023 - 12Z Mon Jan 30 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHEAST AND CENTRAL GULF COAST... 2000 UTC Update -- Very few notable changes with the latest forecast update, based on the latest (12Z) guidance QPF trends (deterministic and probabilistic). A slowly strengthening upper level jet streak will put much of the Slight Risk area in the right entrance region of the jet streak. Small disturbances riding along the jet may locally trigger convection across the Slight Risk area as they race northeastward with the jet. Much of the dynamics for this rainfall event will be in the lower levels of the atmosphere as broad southerly flow covering the whole of the Gulf peaks in intensity as far as the LLJ is concerned over southern LA midday Sunday. The LLJ will reintensify as the convection moves east across the FL Panhandle and southern GA Sunday night, including values as strong as 60 kt over the FL Panhandle, far SE AL and far SW GA. Thus, expect convection to be quite efficient at producing heavy rainfall as it moves eastward Sunday and Sunday night. To be sure, the greatest threat within the Slight Risk area will be across western areas from TX through MS, with slightly lower threats for flash flooding further east. Peak storm total rainfall may exceed 3 inches in portions of southern LA through southern MS-AL-GA, within a more favorable thermodynamic environment with PWs close to 1.75" along with better deep-layer instability (MUCAPEs 500-1000 J/kg). The 12Z HREF in fact indicates clusters of 40-60+ percent probs of >3"/24hrs within the Slight Risk, with the highest probs (60-80%) just north of the Upper TX Coast through much of southwest LA. There continues to be good model consensus however that the axis of heaviest rain will remain north of New Orleans. While main-stem rivers and soil moisture across all of SC remain high, with a few of the main-stems in flood stage, the flashier creeks and smaller tributaries are quite dry, and are likely to handle the 1 to 2 inches of rain expected during the overnight hours Sunday night in this area. Model guidance is in excellent agreement on the swath of heaviest rain falling in the new Slight Risk area. Additional trimming of the Slight Risk was done on the western end with good agreement that metro Houston may largely miss out on the heaviest rain, and also that the heaviest rain will miss the Mississippi River Delta to the north. Confidence wasn't quite there to remove Houston from the Slight given some variability, but extreme southeastern LA was downgraded to a Marginal with this update. Hurley/Wegman Day 3 The Day 3 outlook will be updated by 2030Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!53w1fPoJv5mTFW93bMxvyNt1VjcWcK9eRUn3eyGXIH3t= T4-LY6vw1kZJB_HT36xWKp3zMFlx9tyNBlyaiaNtZptkj6U$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!53w1fPoJv5mTFW93bMxvyNt1VjcWcK9eRUn3eyGXIH3t= T4-LY6vw1kZJB_HT36xWKp3zMFlx9tyNBlyaiaNt9SIzabM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!53w1fPoJv5mTFW93bMxvyNt1VjcWcK9eRUn3eyGXIH3t= T4-LY6vw1kZJB_HT36xWKp3zMFlx9tyNBlyaiaNto_-GLGs$=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) .