Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Sep 14 2025 19:50:47 FOUS30 KWBC 141950 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 350 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 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 neighborhood probabilities for amounts exceeding 3 inches and 5-10 year ARIs. Pereira 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 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF EASTERN NORTH CAROLINA AND SOUTHEASTERN VIRGINIA... As a mid-to-upper level low takes shape over the Southeast, the surface low off of the Southeast Coast is expected to deepen and track north and then northwest toward the Outer Banks by Tuesday=20 morning. Models continue to move into better agreement with the=20 overall track of the system, but show significant spread with=20 respect to QPF. The general consensus of the 12Z HREF guidance=20 keeps the heaviest precipitation confined over eastern North=20 Carolina and far southeastern Virginia, while some other models,=20 most notably the Canadian Regional and Global, spread heavy=20 amounts farther west, closer to the mid-level center. Models=20 generally agree that eastern North Carolina and southeastern=20 Virginia will become the focus for a strong easterly low level jet=20 and deepening moisture (PWs increasing to 1.5-2 inches). While the primary soil types and pre-existing dry conditions may initially=20 limit the threat for runoff concerns, embedded convection may raise rainfall rates, resulting in at least isolated excessive runoff,=20 especially across urbanized areas. Therefore, a Marginal Risk was=20 introduced. The highlighted area leans closer to the 12Z HREF=20 consensus and its higher neighborhood probabilities. Probabilities=20 of amounts exceeding 3 inches are above 50 percent within much of=20 the risk area. Given the noted uncertainty, adjustments including=20 an increase in category cannot be ruled out.=20 Pereira 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/NORTH CAROLINA... 20Z Update... Broadened the Marginal Risk over southeastern Virginia to also include portions of northeastern North Carolina. Some models,=20 including the ECMWF, show additional heavy amounts carrying over=20 into Day 3 across the region -- which given the anticipation of=20 heavy amounts impacting this region on Day 3, may prolong runoff=20 concerns. As on Day 2, continued to lean toward the more easterly=20 guidance. However, given the uncertainty, additional adjustments=20 may be forthcoming. Further west, the upper trough moving across the Rockies has trended slower. The general consensus of the models shows the axis of associated precipitation shifting further west, with many of the models showing their heaviest amounts centered over the flood-resistent Nebraska Sandhills. Therefore, shifted the previous outlook=20 further west, confining the footprint to the more sensitive areas=20 from the southern Nebraska Panhandle to northwestern Kansas. Pereira Previous Discussion... ....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!8pRsiZm5wf4fsGB9HVC5A5m04JVW7wXwUNZDahfh7ARJ= ORN295dcQKML4H_oQqWLH6tDzHfIzdiYyVf2gIxRu89OgHE$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8pRsiZm5wf4fsGB9HVC5A5m04JVW7wXwUNZDahfh7ARJ= ORN295dcQKML4H_oQqWLH6tDzHfIzdiYyVf2gIxRMXa7a0M$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8pRsiZm5wf4fsGB9HVC5A5m04JVW7wXwUNZDahfh7ARJ= ORN295dcQKML4H_oQqWLH6tDzHfIzdiYyVf2gIxRLjTIOT0$=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) .