Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Sep 01 2024 08:17:17 FOUS30 KWBC 010817 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 417 AM EDT Sun Sep 1 2024 Day 1 Valid 12Z Sun Sep 01 2024 - 12Z Mon Sep 02 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF NEW MEXICO/TEXAS, THE NORTHERN GULF COAST, AND THE MID-ATLANTIC... ....Southeastern New Mexico and West Texas... An approaching 250 mb upper trough will move into far West Texas=20 today while a surface boundary lingers across the Hill Country.=20 Precipitable water values are forecast to be around 1.5-1.75" which is about +1 to +2 sigma with the typical NW to SE gradient.=20 Afternoon convection should percolate today and could fall over=20 areas that have seen a few inches of rain on Saturday (with lower=20 FFG values as a result). Coverage should be somewhat isolated so=20 the Marginal Risk will suffice.=20 ....Gulf Coast... Meandering weakness in the mid-lower levels will again help drive=20 some heavier rainfall along the Upper TX Coast into southern=20 Louisiana. Maintained the Marginal Risk as the bulk of the guidance keeps the heaviest rain offshore, though it will be close (again)=20 just like on Saturday.=20 ....Eastern Tennessee Valley and Mid-Atlantic Region... A cold front will approach the Appalchians this afternoon as the=20 lead boundary dissipates, leaving a trough over the coastal plain.=20 The best forcing for afternoon convection will lie there, generally over far southeastern Virginia into central/eastern North Carolina. 00Z HREF probs of exceeding FFG values are around 10-20% (via 1-2=20 inch per hour rates), though there are hints at some higher rates=20 still. Activity should be mostly progressive, suggesting a=20 localized threat of flash flooding. Kept the Marginal Risk for this area. Fracasso Day 2 Valid 12Z Mon Sep 02 2024 - 12Z Tue Sep 03 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE=20 HILL COUNTRY OF TEXAS... ....Texas... Mid-level vort and upper trough will move into West Texas on=20 Monday atop increased moisture from the southeast. Guidance=20 continues to show modest QPF of 1-5 inches near and around the Hill Country, with various foci in the deterministic models. ECMWF-AIFS was still decidedly north compared to the other models. The CSU=20 machine learning first guess fields still suggest a broad Slight=20 Risk over the Hill Country, so at least there is some consistency=20 over the past 24-36 hours in this guidance vs the models (which is=20 the point). FFG values are lowest near/south of San Angelo to Del=20 Rio (due to recent rain) where the HREF probs of exceeding these=20 values reach ~50%. ....Carolinas... Cold front will sink farther into the Carolinas from day 1, which=20 will nudge the excessive rainfall threat south as well. Best=20 dynamics move offshore with the trough axis so the Marginal Risk=20 should cover any remaining isolated flooding threat due to=20 afternoon convection. Fracasso Day 3 Valid 12Z Tue Sep 03 2024 - 12Z Wed Sep 04 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR TEXAS... ....Texas... Mid-level vort will be exiting the region though precipitable=20 water values will remain high (+1 to +2 sigma initially, then=20 decreasing late Tuesday). Depending on how much (and where) rain=20 falls on day 2, there is room to upgrade some of this region to a=20 Slight Risk pending better model agreement in future runs. For now, ensemble consensus is just east of the Hill Country but individual models are quite varied north/south. First guess fields from the=20 CSU machine learning algorithm do show a Slight Risk outline,=20 lending credence to a future upgrade.=20 Fracasso Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-Qipffhs2DHEV-NTMGMUukwuDCkmvlshDbQVkylGZJII= HaCguFwZjQ-YOyL8jspoqutaFTf9wCIN8A88gLXTatILyKU$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-Qipffhs2DHEV-NTMGMUukwuDCkmvlshDbQVkylGZJII= HaCguFwZjQ-YOyL8jspoqutaFTf9wCIN8A88gLXTtNBfer4$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-Qipffhs2DHEV-NTMGMUukwuDCkmvlshDbQVkylGZJII= HaCguFwZjQ-YOyL8jspoqutaFTf9wCIN8A88gLXTGxrPDX8$=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) .