Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Sep 14 2025 16:01:13 FOUS30 KWBC 141601 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1201 PM EDT Sun Sep 14 2025 Day 1 Valid 16Z Sun Sep 14 2025 - 12Z Mon Sep 15 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN THE CENTRAL=20 DAKOTAS... 16Z Update... Made only minor adjustments to the previous outlook areas. This included narrowing the footprint of the Slight Risk area over the Dakotas. The 12Z hi-res models are in generally good agreement, indicating a narrow stripe of heavy amounts extending north from south-central South Dakota to north-central North Dakota. The Slight Risk reflects the area where the 12Z HREF shows high=20 neighborhood probabilities for amounts exceeding 3 inches and 5-10=20 year ARIs. Pereira=20 Previous Discussion... ....Northern Plains... Upper trough exiting the Rockies has split off its southern portion into an upper low that will move onto the High Plains later this morning. Southerly flow will continue across the Northern Plains along with ample moisture -- PW anomalies +2 to +3 sigma -- as a surface low over SD moves northward later this afternoon. Convergent flow toward the nose of the sfc-based instability gradient just to the east is expected to promote some south-to- north convection that may overlap areas that saw a few inches of rain on Saturday. Maintained the Slight Risk outline here with a Marginal Risk buffer extending to the south to the edge of the Sand Hills. ....Central and Southern Plains... Split the longer Marginal Risk area from the previous forecast into its own entity and extended it even farther southward to the Mexican border to account for another tick up in expected convection from KS southward to TX. Storms should fire along and ahead of a low-level confluence axis and within a stripe of deeper moisture. Some of these areas in W TX saw a couple/few inches of rain on Saturday and FFG values are lower. Some models do indicate the potential for slow-moving or backbuilding cells, resulting in locally heavy amounts and perhaps isolated flash flooding concerns. Fracasso Day 2 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 Day 3 Valid 12Z Tue Sep 16 2025 - 12Z Wed Sep 17 2025 ....THERE ARE MARGINAL RISKS OF EXCESSIVE RAINFALL IN SOUTHERN NEW MEXICO, THE CENTRAL PLAINS, AND COASTAL VIRGINIA... ....Southern New Mexico... Moisture will start to nudge upward over southern NM (though much more well west of there) with some afternoon instability and expected isolated convection, mainly over the mountains close to the Mexican border. Low-end Marginal Risk is outlined here though activity should be rather isolated. ....Central Plains... Positively-tilted trough over the Northern Rockies will move eastward to the High Plains Tuesday afternoon. Broad westerly mid- level flow amid increasing moisture will help fire off some storms over at least NE near the better forcing but also southward into KS. A Marginal Risk is outlined here for an isolated flash flood threat. ....Coastal Virginia... Over the past couple of days, the models have trended toward bringing in an area of low pressure near the Outer Banks Tuesday morning or so. Rain should spread inland on Monday with additional and perhaps heavier rain on Wednesday. This area has been rather dry recently and rain rates may not be all that high, but some convection-driven rain is possible depending on the flavor of this area of low pressure. A Marginal Risk is depicted for southeastern/coastal Virginia and far northeastern North Carolina but with a lot of uncertainty in the rainfall pattern/rates/duration. Fracasso Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!43gDcxjrzfQPFqwB3NPeqY5KIp9THWswbO63JA0Lj3i1= rv6W3y0mgcWCaCEyyESquMtYEtMbVdikTjZRQsiiHmAWB9U$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!43gDcxjrzfQPFqwB3NPeqY5KIp9THWswbO63JA0Lj3i1= rv6W3y0mgcWCaCEyyESquMtYEtMbVdikTjZRQsii2tATJVo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!43gDcxjrzfQPFqwB3NPeqY5KIp9THWswbO63JA0Lj3i1= rv6W3y0mgcWCaCEyyESquMtYEtMbVdikTjZRQsiii0DDd74$=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) .