Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Aug 16 2025 08:53:23 FOUS30 KWBC 160852 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 452 AM EDT Sat Aug 16 2025 Day 1 Valid 12Z Sat Aug 16 2025 - 12Z Sun Aug 17 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF=20 THE UPPER MIDWEST, SOUTHERN NEW MEXICO, AND SOUTH-CENTRAL TEXAS... ....Upper Midwest and Northern Plains... Well organized MCS over eastern SD early this morning will continue to track east over southern MN rest of this morning and likely into WI around midday. Cells developing ahead of the severe line as well as MCV/bookend development will make for a repeating heavy rain/flash flood threat along the the path. The boundary from this system will play a role in nocturnal convection tonight which=20 could also be quite heavy and over similar areas of MN/IA/WI and may warrant a Moderate Risk upgrade. Otherwise, until then the Slight Risk is expanded west across southern MN and includes more of northern IA with the Driftless area of WI up through the Twin Cities considered a higher end Slight area.=20 The lingering frontal boundary over SD and into far eastern MT warrants maintenance of the Marginal Risk over that portion of the Northern Plains for redeveloping storms tonight. ....South-Central Texas, Along Gulf Coast and Southeast... Tropical disturbance remnants (had been AL98) are south of Laredo with southerly flow bringing associated tropical moisture north toward the Texas Hill Country. Convection has developed southwest of San Antonio and will continue to grow as it lifts north to the Hill Country. The 00Z HREF had good consistency with this and with input from WFO EWX, there is now a Slight Risk for this morning threat with potential for 2-4" and locally higher through 18Z. Please monitor WPC MPDs and local WFO products for updates on this heavy rainfall threat area. To the east of the Texas Hill Country and along the Gulf Coast up to the southern Appalachians and northern FL Peninsula is elevated moisture, generally 1.5 sigma above normal. Isolated excessive rain/flash flood potential is present today through this broad region much like recent days (though focused farther south as the upper ridge continues to shift the forcing south). ....Southwest... Monsoonal moisture plume should focus farther east today,=20 shifting the potential for isolated flash flooding across southeastern Arizona, and much of central/southern New Mexico.=20 CAMs continue to support Sacramento Mountains (and just east) focused activity as well as directly west, where the Slight Risk remains. ....Northwest and Northern Rockies... Marginal risk remains across far north-central California and much of central/eastern Oregon with an expansion across northern ID and western MT. Elevated moisture from the record high moisture atmospheric river (Salem OR had its highest PW on record at 00Z) develops into a ribbon across these areas during peak heating today which should produce isolated flash flood threats. Some of the=20 heavy rainfall could occur atop burn scars, locally enhancing=20 runoff potential. Jackson Day 2 Valid 12Z Sun Aug 17 2025 - 12Z Mon Aug 18 2025 Fri Aug 15 2025 - 12Z Sat Aug 16 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A PORTION OF THE UPPER MIDWEST... ....Northern Plains through the Upper Midwest... Continued activity from late tonight into or through Sunday morning is expected along residual/frontal boundaries over portions of the Midwest, likely including potential repeat areas in southern MN=20 and western WI. This activity is developing in an elevated moisture atmosphere along northern extent of upper ridge focused over the=20 central CONUS. Guidance is quite varied across the Upper Midwest with the Canadian Regional keeping the heaviest focus over northern MN/eastern ND, the 00Z FV3LAM a bit farther south from eastern ND=20 to northwestern WI, the 00Z RRFS over southern MN. The 06Z NAMnest and HRRR also have a southern MN focus which is where the Slight Risk remains, though the Marginal Risk was expanded north to accommodate more of the northern solutions. Given all the boundary and mesoscale interactions that will take place today and tonight, there is remaining uncertainty which will hopefully come into better focus with guidance later today.=20 Moisture from the atmospheric river pushing over the Northwest and northern Rockies through tonight extends over the northern Plains on Sunday. Given broad area of instability, frontal forcing, and=20 PW of 1 to 2.5 sigma above normal, a Marginal Risk remains for much of MT and the Dakotas. ....New Mexico... Continued monsoonal moisture over New Mexico on Sunday between=20 flow from a trough off the West Coast and a ridge over the central=20 US. Will need to monitor areas for upgrades, but for now a Marginal Risk remains in effect for much of NM and far west TX. ....Florida to the Central Gulf Coast... Focus of elevated PW (2 to 2.25" which is 2 sigma above normal) across northern FL through the central Gulf Coast from ridge centered over the central states. The Marginal Risk remains for=20 the northern half of the FL Peninsula into southern GA and west through Mobile, AL remains in effect.=20 Jackson Day 3 Valid 12Z Mon Aug 18 2025 - 12Z Tue Aug 19 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR NEW MEXICO AND THE GREAT LAKES... ....Great Lakes... The persistent frontal pattern over the Upper Midwest begins to move east Monday night. Until then, continued organized activity=20 can be expected to redevelop over similar areas from recent days in Iowa/Wisconsin before shifting across Michigan. Elevated moisture rounding upper high pressure centered over the central states will continue to fuel heavy rain potential with impulses/the frontal pattern to aid lift. There is notable uncertainty with most global guidance and the Canadian Regional focusing heavy rain closer to Lake Michigan while the 00Z RRFS and the 03Z SREF is focused more in Iowa/southern Minnesota. The broad Marginal is maintained for now with notes that a more focused area of heavy rain is likely (shrink the outlook area) and if that were to be particularly=20 heavy and/or over areas impacted from heavy rain between now and=20 then, an upgrade would be necessary. ....New Mexico and Far West Texas... Continued monsoonal moisture advection continues to result in terrain based initiation with an isolated flash flood threat. The Marginal Risk was expanded to include most of New Mexico and a=20 little more of Far West Texas and southeast Arizona. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9aBnZpDq0P6DCgf2YWC9unVBprvrRzKLvG0XwueW3qf-= ByK7r-qAHvmNcWVmcifgLs30b87EfqaU1GRgWuZyTwBGxOk$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9aBnZpDq0P6DCgf2YWC9unVBprvrRzKLvG0XwueW3qf-= ByK7r-qAHvmNcWVmcifgLs30b87EfqaU1GRgWuZyMRIXS5E$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9aBnZpDq0P6DCgf2YWC9unVBprvrRzKLvG0XwueW3qf-= ByK7r-qAHvmNcWVmcifgLs30b87EfqaU1GRgWuZycNH_S1A$=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. 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