Subj : HVYRAIN: Excessive Rainfa To : All From : Mike Powell Date : Sat Sep 13 2025 09:39:03 FOUS30 KWBC 130849 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 449 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 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 slowly eastward and take on a negative tilt, with a continued influx of moisture (PW anomalies +2 sigma) into the Southern Rockies and points northward. As the trough axis crosses the Four Corners region around 00Z tonight, LLJ increase will support convection over eastern NM late afternoon that will push into West Texas in the evening. Storms may have enough forward speed to limit flash flooding potential, but 00Z CAMs continue to show potential for 1-4" amounts. Focused the Slight Risk outline further from the previous shifts to the best ensemble agreement. ....Northern Plains... Southerly flow through the column will maintain a surge of moisture (PW anomalies +3 sigma / 1.50") into the Northern Plains as weaker shortwaves race northward ahead of the main upper low over MT. Recent CAM guidance still shows some east-west displacement of heaver north-to-south QPF maxima, owing to small differences in shortwave/sfc boundary interactions and any morning convection. Maintained the Slight Risk outline over western ND but the eventual QPE footprint will likely be much narrower. ....Northeastern Illinois and surrounding areas... Shortwave diving southeastward out of Wisconsin this morning at the nose of a jet streak will help organize a small area of at least modest rainfall around the Chicagoland area that continues SSE-ward this afternoon. Some 00Z CAM guidance remains rather bullish with 2-3" amounts which may be enough to cause some urban runoff issues. ....South Florida... Frontal boundary will remain just to the southeast of Florida, but precipitable water values will start the day around 2 inches. Drier air will slowly work southeastward through the entirety of the Peninsula by the end of the day, and have targeted the Marginal Risk outline to around the urban areas between Palm Beach and 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 portion into an upper low over western Nebraska midday Sunday, with southerly flow continuing across the Northern Plains (and ample moisture -- PW anomalies still +2 to +3 sigma). This mid-level low will lift northward and act as a focus for convergence toward the nose of the sfc- based instability gradient just to the east. Storms may repeat over the same area as D1, with the potential for another 1-2"+ of rain. Maintained the Slight Risk outline here with a broader Marginal Risk extending to the south where the guidance shows potential for 2-4" of rainfall, but over areas with higher FFG values (esp. the Sand Hills). 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. Fracasso $$ --- SBBSecho 3.28-Linux * Origin: ILink: CCO - capitolcityonline.net (454:3/105) .