Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Sep 13 2025 08:21:56 FOUS30 KWBC 130821 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 421 AM EDT Sat Sep 13 2025 Day 1 Valid 12Z Sat Sep 13 2025 - 12Z Sun Sep 14 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR EASTERN NEW=20 MEXICO INTO FAR WEST TEXAS AS WELL AS FOR WESTERN NORTH DAKOTA... ....Central High Plains through Southern Rockies/West TX... Upper trough over the Great Basin this morning will continue=20 slowly eastward and take on a negative tilt, with a continued=20 influx of moisture (PW anomalies +2 sigma) into the Southern=20 Rockies and points northward. As the trough axis crosses the Four=20 Corners region around 00Z tonight, LLJ increase will support=20 convection over eastern NM late afternoon that will push into West=20 Texas in the evening. Storms may have enough forward speed to limit flash flooding potential, but 00Z CAMs continue to show potential=20 for 1-4" amounts. Focused the Slight Risk outline further from the=20 previous shifts to the best ensemble agreement.=20 ....Northern Plains... Southerly flow through the column will maintain a surge of=20 moisture (PW anomalies +3 sigma / 1.50") into the Northern Plains=20 as weaker shortwaves race northward ahead of the main upper low=20 over MT. Recent CAM guidance still shows some east-west=20 displacement of heaver north-to-south QPF maxima, owing to small=20 differences in shortwave/sfc boundary interactions and any morning=20 convection. Maintained the Slight Risk outline over western ND but=20 the eventual QPE footprint will likely be much narrower.=20 ....Northeastern Illinois and surrounding areas... Shortwave diving southeastward out of Wisconsin this morning at=20 the nose of a jet streak will help organize a small area of at=20 least modest rainfall around the Chicagoland area that continues=20 SSE-ward this afternoon. Some 00Z CAM guidance remains rather=20 bullish with 2-3" amounts which may be enough to cause some urban=20 runoff issues.=20 ....South Florida... Frontal boundary will remain just to the southeast of Florida, but precipitable water values will start the day around 2 inches.=20 Drier air will slowly work southeastward through the entirety of=20 the Peninsula by the end of the day, and have targeted the Marginal Risk outline to around the urban areas between Palm Beach and=20 Miami. Fracasso Day 2 Valid 12Z Sun Sep 14 2025 - 12Z Mon Sep 15 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN THE WESTERN DAKOTAS... ....Central and Northern Plains... Upper trough exiting the Rockies will split off its southern=20 portion into an upper low over western Nebraska midday Sunday, with southerly flow continuing across the Northern Plains (and ample=20 moisture -- PW anomalies still +2 to +3 sigma). This mid-level low=20 will lift northward and act as a focus for convergence toward the=20 nose of the sfc- based instability gradient just to the east.=20 Storms may repeat over the same area as D1, with the potential for=20 another 1-2"+ of rain. Maintained the Slight Risk outline here with a broader Marginal Risk extending to the south where the guidance=20 shows potential for 2-4" of rainfall, but over areas with higher=20 FFG values (esp. the Sand Hills).=20 Fracasso Day 3 Valid 12Z Mon Sep 15 2025 - 12Z Tue Sep 16 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent.=20 Fracasso Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4C0nHySZf64ZtaUVpDE4lb0PEKah4Yk-GUbb_TwaptTq= oEYJEeaDPun8HkGpTxZuWW0JaVgCQRP1tFH7aHLGQhgxI7o$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4C0nHySZf64ZtaUVpDE4lb0PEKah4Yk-GUbb_TwaptTq= oEYJEeaDPun8HkGpTxZuWW0JaVgCQRP1tFH7aHLGZ8DGRqo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4C0nHySZf64ZtaUVpDE4lb0PEKah4Yk-GUbb_TwaptTq= oEYJEeaDPun8HkGpTxZuWW0JaVgCQRP1tFH7aHLGldirx2A$=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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .