Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun May 25 2025 00:52:52 FOUS30 KWBC 250052 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 852 PM EDT Sat May 24 2025 Day 1 Valid 01Z Sun May 25 2025 - 12Z Sun May 25 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE OZARKS AND MID-SOUTH... 01Z Excessive Rainfall Discussion... No fundamental shift in forecast reasoning from previous outlook. Did expand the Marginal and Slight risk areas a bit westward given the uncertainty about where the storms will fire that build southeast into the outlook areas. The expectation is that the convection will grow in areal coverage and intensity once the low level jet develops and rides north of a quasi-stationary boundary draped across the Plains later tonight. Also extended the Marginal risk area southwest into Texas along and ahead of storms that were developing along/near the dryline within a very unstable environment. Given a slow westward motion noted on satellite...any downpours may last long enough to produce isolated instances of flooding (mainly in regions of poor drainage). Bann ....Previous Excessive Rainfall Discussion... ....South-Central Plains through Mid-South into the Southeast... 16Z Update... Organized mesoscale systems continuing this morning over eastern OK, central AR and some activity over northern MS/AL. This activity is waning with IR satellite imagery depicting warming trends. There is general agreement among 12Z CAMs for afternoon redevelopment over southeast KS/northeast OK over the Plains and propagating southeast over eastern OK, southeast MO and much of AR which all saw heavy rain over the past day (except for northwest AR which was largely avoided). These storms should once again produce heavy rainfall rates, per 12Z HREF with probabilities for 3 inches in three hours and RAP guidance renewing 1.75 inch PW on the continued southerly flow from the Gulf. Extra caution should be given through the greater Ozarks region given this holiday weekend with greater activity in and around flash flood prone areas. Frontal convergence farther east through northern GA will allow scattered heavy development where the Marginal Risk was expanded through. ....Central High Plains... Moist low level easterly flow maintains PWs of 0.75 to 1 inch (2+ standard deviations above normal), which along with mid-level energy and right entrance region jet forcing, will continue to support storm development with locally heavy rainfall over the High Plains with afternoon development east from the Laramie Mountains and Front Range. Slow storm motions could allow local rainfall of 2 to 3 inches. The Marginal Risk was expanded over western Neb and southeast WY with some shrinking along the I-25 corridor in CO. Jackson Day 2 Valid 12Z Sun May 25 2025 - 12Z Mon May 26 2025 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM CENTRAL OKLAHOMA INTO THE OZARKS... ....Southern Plains through the Ozarks and Mid-South... 21Z Update... Expanded the Moderate Risk south and west to include central Oklahoma and more of northwest Arkansas. Convective activity tonight looks to focus along a broad swath over southern KS, eastern OK and southern MO and shift southeast early Sunday over eastern/central OK and northern AR where a stationary front is likely to remain. Strengthening southerly winds ahead of an amplified trough moving across the Southwest will support deepening moisture along the front and an increasing threat for heavy rainfall back across southwestern Oklahoma and along the Red River Valley. With these repeating events expected to bring additional rain of 2 to 4 inches with locally higher, the Slight Risk was expanded to include much of OK as well as more of AR. While the better organized and heaviest amounts are expected to center over Oklahoma through the Ozarks, there is the potential for localized heavy amounts and isolated flash flooding to spread east along the frontal boundary through the Tennessee Valley, north Georgia (including Atlanta) and much of South Carolina where a Marginal Risk has been expanded through. .....Front Range/Central High Plains... Moisture and forcing will remain favorable for a diurnal focus to locally heavy rain starting on the Front Range Sunday afternoon and spreading west in the mean flow across the central High Plains. A Marginal Risk remains in effect for northeastern Colorado, the Nebraska Panhandle, far southeast Wyoming into southwest South Dakota. Jackson Day 3 Valid 12Z Mon May 26 2025 - 12Z Tue May 27 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE SOUTHERN PLAINS TO THE TENNESSEE VALLEY... 21Z Update... While some additional heavy rains are possible in eastern Oklahoma and across the Ozarks, the greater threat is expected to be farther south than recent days as an upper trough axis ejects from the Southwest over the southern Rockies and onto the southern Plains Monday. This will push the front and deeper moisture farther south. Adjustments with the 12Z suite of guidance today is that the moist southwesterly flow with energy aloft will support an axis for storms over central/North Texas (farther west than prior runs) through the Tennessee Valley. The Slight Risk was maintained with expansion to the west over Texas. A targeted upgrade is likely should these trends continue, though much of North and eastern Texas have been fairly rain free over the past week with flash flood guidance near their normal high values. The motion of the upper trough axis over the Plains Monday night should allow nocturnal activity over the central Plains. An arm to the Marginal Risk was extended up through the KC metro into southeast Nebraska for now, with a note that details on Plains heavy rain threat areas should come into better focus over the coming days. Jackson Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8Pn2KkJyz_seMVZUte6NJnJ4kKzn-5llahKfROQM6xaK= ByRlTS5HQqqEMt3isNn7UPWmk-ZaaCdhVDVfZWiz8jiDrTM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8Pn2KkJyz_seMVZUte6NJnJ4kKzn-5llahKfROQM6xaK= ByRlTS5HQqqEMt3isNn7UPWmk-ZaaCdhVDVfZWizkN2BhBc$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8Pn2KkJyz_seMVZUte6NJnJ4kKzn-5llahKfROQM6xaK= ByRlTS5HQqqEMt3isNn7UPWmk-ZaaCdhVDVfZWizmcWMoLs$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .