Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jul 25 2025 01:01:00 FOUS30 KWBC 250059 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 859 PM EDT Thu Jul 24 2025 Day 1 Valid 01Z Fri Jul 25 2025 - 12Z Fri Jul 25 2025 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF EASTERN KANSAS AND NORTHWESTERN MISSOURI... ....0100Z Update... ....High Plains into the Midwest... Moderate Risk across eastern KS and northwestern MO was mostly maintained and only shifted a bit southwest with this update based on latest CAMs and WoFS output. This also aligned with the southern push in the initial line of thunderstorms developing this=20 afternoon along a pre-frontal trough extending as far south as the TX Panhandle. It remains likely that throughout the night activity slowly lifts northward as the LLJ increased in strength and a mid- level shortwave ejects out of the southern High Plains, with activity becoming more aligned with the analyzed just to the north bisecting KS from southwest to northeast and reaching into far northwest MO. Slow propagation of storms and mean layer winds=20 parallel to the developing instability gradient/draped frontal=20 boundary remains concerning overnight given the very high PWs=20 (2.0-2.5") across the region. However, there remains some short term uncertainty with respect to how widespread or significant flash flooding impacts may be and where exactly within/near the MDT Risk they occur. 23z WoFS output through 05z isn't as impressive with rainfall rates as the line of thunderstorms begins to lift back northward across central and eastern KS, with 90th percentile totals only around 2-3". After 05z though, thunderstorms could blossom in response to an approaching=20 mid-level wave or MCV ejecting out of the TX/OK Panhandle and could be the catalyst for more widespread flash flooding impacts along a boundary spanning from central/eastern KS into northwest MO.=20 2500-3000 J/kg of MLCAPE is expected to be available per the 00z=20 RAP during this timeframe, which is sufficient for the maintenance=20 of thunderstorms. The 18z RGEM is most aggressive with this high-=20 end scenario and while potentially very overdone in QPF, has a=20 similar axis to the greatest 6-hr neighborhood probabilities for=20 exceeding 3" in both the HREF and REFS. Regardless, scattered=20 instances of flash flooding are considered likely within the MDT=20 Risk, but are also possible within a broader SLGT Risk extending=20 from the High Plains of northeast NM and southeast CO into northern IL and IN along this same frontal boundary. Isolated significant=20 flooding impacts are most likely within the MDT Risk, where=20 localized rainfall totals over 5" are possible and could overlap=20 with urban areas such as Topeka and Kansas City. Be sure to follow=20 subsequent MPDs for more short term updates. ....Southeast... The presence of a slow-moving surface reflection and eastward progressing upper trough across the northern Gulf will lead to another period of heavy rainfall within the confines of the Gulf Coast tonight. With PWATs remaining up inside the 90-99th=20 percentile along the immediate coast and suitable instability=20 presence, the previous MRGL was maintained along the central Gulf Coast where the greatest southerly flow and coastal enhancement is possible overnight. ....Northern California and Adjacent Areas... A narrow tongue of elevated moisture on the northern periphery of a closed upper reflection along the CA coast will continue a period=20 of thunderstorms within the northern Sierra's through northern CA=20 and southern OR early tonight. PWATs running ~1 standard deviation above normal and MUCAPE between 500-1000 J/kg should be sufficient for scattered convective initiation along the ridges which could=20 easily produce local 0.5-1+" of precip in a short time. The=20 previous MRGL risk was generally maintained with only minor=20 adjustments. Snell Day 2 Valid 12Z Fri Jul 25 2025 - 12Z Sat Jul 26 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE CENTRAL PLAINS, MIDWEST, AND OHIO VALLEY... ....Central Plains into Ohio Valley... ....1900Z Update... Minimal changes were made to the ERO, based on the latest (12Z) model suite. Hurley ....Previous Discussion... The combination of robust moisture and the presence of both a surface low progression out of KS and a slow-moving cold front will lead to yet another day of heavy rainfall across portions of the Central Plains into the central part of the Midwest. Guidance has been struggling to ascertain how the this period will evolve, but the past 00z NWP has come into a bit better agreement on some of the ingredients that would lead to another round of heavy rainfall in-of central and eastern KS and points northeast. The key will be the migration of the surface low across KS. At this juncture, it's pretty likely the low center will move into northeast KS by Friday morning with ongoing convection, potentially with some MCV driven components that would lead to a relatively active beginning of the D2. Even if convection trends down for the initial 6hr window, general diurnal destabilization around the low will lead to another round of thunderstorm genesis in proximity to the surface reflection and points northeast. This puts a higher threat for overlapping days of heavy convection across northeast KS into northwest MO in the first 12hr period before focus shifts northeast into IA as the low lifts northeast around the northwestern periphery of the ridge. Any additional rainfall over the KS/MO area could spell trouble if the D1 works out to how some of the CAMs are indicating. The trend is leading to further compromised soils and perhaps even remnant flooding if another round of heavy rain breaks out not long after impacts from the previous evening. The threat for rainfall totals between 2-4" with locally higher maxima across northeast KS, northwest MO, and southern IA is gaining steam with an unwavering signal the past 5 runs from the AIFS ensemble QPF distribution. Granted, convective schema is hard to pin down at leads, but the synoptic progression would favor heavy precip across these areas with even some inference of heavy convection through northern IL and IN thanks to the environment in place along the front. A SLGT risk was extended back west and southwest for the growing signal with a high end SLGT forecast across the aforementioned 3 zones in KS/MO/IA. This period could have some short term shifts pending convective evolution in the D1, so stay tuned for future updates. ....Gulf Coast... The disturbance across the northern Gulf will continue to slowly migrate to the west with an attendant surface low remaining situated just south of the west-central Gulf coast. Low center proxy will be the ultimate factor in the prospects of very heavy rainfall along the immediate Upper TX coast back into LA. So long as the low center remains far enough offshore, the greatest low- level convergence pattern and persistent area of convection could remain just off the coast to limit impacts. However, the airmass surrounding the disturbance will still be pretty robust with PWATs remaining very high (>2.3") for much of the immediate coastal plain over TX back through the central Gulf coast. The National Hurricane Center is maintaining a 10% within the latest Tropical Weather Outlook over the northern Gulf for the next 2-3 days, so any tropical characteristics from this disturbance could enhance flash flood prospects further, especially when it moves closer to the Upper TX coast. ....Northern Plains... A quick moving shortwave ejecting out of the Rockies is forecast to impact the Northern Plains on Friday night into early Saturday with scattered thunderstorms likely to roll through the Dakotas after sunset. Increased regional PWATs upwards of +2 deviations along with ample mid-level forcing will be enough for a period of enhanced heavy rainfall prospects during the time frame of impact. Deterministic output is all over the place in exact convective placement and magnitude, however signals for 2-4" of rainfall in a short period of time would be sufficient for at least low-end MRGL prospects up across parts of the Dakotas. Timing of the shortwave will be key for the threat, but there was enough consensus on their being a chance for a maintenance of the MRGL risk inherited. Kleebauer Day 3 Valid 12Z Sat Jul 26 2025 - 12Z Sun Jul 27 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE GREAT LAKES, OHIO VALLEY, NORTHERN PLAINS, WESTERN AND CENTRAL GULF COAST, NORTHEAST CALIFORNIA AND NORTHWEST NEVADA... ....Midwest through Great Lakes and parts of the Mid Atlantic... ....1900Z Update... Based on some of the guidance trends, including the 12Z ECMWF, the 06Z EC-AIFS, and GEM, have expanded the Marginal Risk a bit farther east into northern parts of the Mid Atlantic. This given the continued high TPW anomaly and destabilizing airmass aloft (increasing chances for at least elevated convection later Sat into Sat night). Hurley ....Previous discussion... Disturbance across the Plains will move northeast into the Midwest and eventually the Great Lakes with heavy rain prospects carrying through the region. This is marking the end of a persistent heavy rain setup for the past several days with guidance indicating the highest potential over IA, northern IL and southern WI. Ensemble trends have shifted to places along and north of I-80 seeing the greatest potential for 2+" of rainfall at any point in the D3 period, however there's still some uncertainty on specifics of where the heaviest core of precip will occur when assessing individual deterministic, so the current MRGL forecast was sufficient for this time. That said, there's a good chance we will see an upgrade at some point in the next series of updates, but details will need to be ironed out on the previous periods of convection before initiating the upgrade. ....Gulf Coast... The remnants of the migrating upper trough and surface low will remain situated across the western half of the Gulf with the main area of surface reflection likely coming ashore into TX during the period. Models are truly all over the place when it comes to the convective expanse during the D3 time frame with some guidance having little development to others showing a formidable mass of precip over LA and the Upper TX coast. In any case, the deep tropical moisture presence and general instability will be pretty high across the immediate Gulf coast with the ML outputs relatively favorable for at least scattered heavy convection along and south of I-10. In coordination with local WFO's across the central and western Gulf coast, maintained a MRGL risk with emphasis on the immediate coastal plain where instability points to more favorable heavier precip potential. ....Northern Plains... A second potent shortwave will eject northeast out of the northern High Plains with another round of heavy precip potential with more organized convective clusters migrating through the Dakotas. Signature has bounced around on the exact placement of the multi- cell organization, but probabilities from the latest NBM and AIFS Ensemble indicate more of northeastern ND as the primary area of interest. Look for local 2-3" maxima, at the very least with this type of setup. The good news is the pattern looks relatively progressive, so outside some near term mesoscale trends for repeating cell action, the threat remains firmly in the MRGL risk stance. ....Northeastern California and Northwest Nevada... Almost a carbon copy of the prior period for convective impacts lingering across the Northern Sierra up through northeastern CA and northwest OR. The upper pattern is pretty slow to breakdown with the diffluent area in the longwave setup still situated over northern CA into NV. Modest instability and slightly above normal moisture in the terrain will offer the capability for some isolated flash flood concerns within any complex terrain and burn scar remnants in the above area. Precip maxima will be limited to ~1", so the threat lies within the lower threshold of a MRGL risk, which is what is now forecast. Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7b1C26ksWCqo7HtyDRpNsNu0eRDTPH7vXgKjSzJadIVs= Ul8l-6YqozbaRN9ZpB7uO_nmPrzyIo7vbL2N6pf4PjTDhXI$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7b1C26ksWCqo7HtyDRpNsNu0eRDTPH7vXgKjSzJadIVs= Ul8l-6YqozbaRN9ZpB7uO_nmPrzyIo7vbL2N6pf4ivehW-0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7b1C26ksWCqo7HtyDRpNsNu0eRDTPH7vXgKjSzJadIVs= Ul8l-6YqozbaRN9ZpB7uO_nmPrzyIo7vbL2N6pf4ckvOIIE$=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) .