Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jul 24 2025 18:52:38 FOUS30 KWBC 241851 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 251 PM EDT Thu Jul 24 2025 Day 1 Valid 16Z Thu Jul 24 2025 - 12Z Fri Jul 25 2025 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF NORTHEASTERN KANSAS AND NORTHERN MISSOURI... ....High Plains into the Midwest... ....1600Z Update... Based on collaboration with TOP and EAX, have hoisted a targeted Moderate Risk area over far northeastern KS into parts of northwest and north-central MO -- including the Topeka and KC metro areas. While still dealing with remnant convective debris and stability, expect deep-layer destabilization later this afternoon and evening. Impressive TPW anomaly originating off the west coast of Mexico, 2-2.5 standard deviations above normal, continues along/ahead of the surface frontal boundary. Observed 2.14" PW at Topeka KS was very close to the daily record (2.16"). Meanwhile, it still appears some semblance of right-entrance region influence well south of the upper jet streak will help the late afternoon activity upstream grow upscale this evening and overnight, eventually giving way to MCV lobes. Always concerned about the "Maddox Frontal" setups like this, even with the LLJ 30kts or less, considering deep layer moisture anomaly and with the alignment of the LLJ and mean 850-300 mb flow (i.e. light northeasterly Corfidi vectors, opposing the low- level inflow). Based off the 00Z run, the EC EFI does hint at the potential for something more significant, especially over the urban corridor between Topeka and KC, where the rainfall the past 10-14 days has been between 300-600% of normal. Hurley ....Previous Discussion... Active pattern across the Central CONUS continues through Thursday with another round of heavy convection likely in proximity to a steady moving cold front from the north. At the surface, cold front analyzed over the Northern Plains and Upper Midwest will make headway to the south and southeast with a greater latitudinal push west of the Mississippi due to a strong sfc-500mb ridge axis nestled across the Southeastern U.S. The general southwest to northeast alignment will be precursor to the expected mean cell motions for the period with emphasis on convective development likely from the OK panhandle up through KS/MO/IL/IA during the late-afternoon and evening time frame. Initial impacts will be felt further north in the first 6hr window of the period, but the forward propagation of the convective cluster migrating out of IA/NE should lose some strength in the morning as LLJ weakens and cold pools run out ahead of the main bulk of precip. Still, some embedded heavier cores could cause issues along and north of I-80 latitude leading to a MRGL and SLGT risk maintenance over eastern IA into northern IL. As we move into the afternoon and evening, attention will turn to the southwest from the initial impact areas with a broader focus over northeast NM and points northeast through KS/northwest MO as the next round of heavy convection takes shape. A sharp theta_E gradient will likely denote the position of the cold front with a long run of surface-850mb convergence located within the confines of the front as it bisects the above areas. Surface low off the High Plains of southeast CO will slowly move east-northeast into the High Plains of KS by late-afternoon allowing for a maturing south to southeast in-flow within the eastern flank of the low which will set the stage for ample moisture pooling and strengthening low-level convergence signature referenced above. Convection will fire under the low's influence across southwest KS into the adjacent OK/TX panhandles with mean cell motions relatively weak within the low's proximity. Further to the east, general destabilization in the warm sector will further convective development over eastern KS into northwest MO with increasing training potential as Corfidi vectors indicate a weakening upshear wind profile as we move into the evening, especially in the confines of the front. Heavy rainfall potential is elevated due to the deep moisture presence across the Central and Southern Plains with a strong consensus in both deterministic and ensembles for >2" PWATs located over central and eastern KS up into the northern half of MO. 00z HREF neighborhood probs for >3" are between 50-80% over a large portion of KS with the highest probs over northeastern KS near Topeka and along the I-70 corridor. Probs for >5" are running between 20-35% for the same areas. Areal average of 2-3" is fairly pronounced within the means, but the key is some of the deterministic from CAMs, and even some of the globals are indicative for local maxima between 4-7" with even a few 8+" thrown in for good measure. This setup is one that could entice an upgrade in future updates with the highest potential likely over eastern KS into northwest MO due to wetter antecedent soils and lower FFG's compared to areas back into southwest KS. That being said, this is one setup to keep a close eye on as locally significant flash flood potential is becoming more favorable as we step through the forecast cycles. If the probs trend even more favorable, there would be merit to see a targeted upgrade. For now, a broad SLGT risk with high end SLGT embedded over eastern KS into MO. ....Central and Southern Rockies... Isolated to widely scattered convection will initiate, once again across the Front Range back into the Central and Southern Rockies with localized maxima likely contributing to scattered flash flood prospects in their wake. The primary ascent pertains to the diffluent area ahead of the closed reflection over CA through the forecast period. Enough of a deep moisture presence and modest instability up through the Continental Divide and points east will be suitable for another day of convection with the best opportunity for flash flooding likely located in proximity of the complex topography centered over northern NM through CO and southeast WY. HREF probs indicate a general 1-3" type maxima in any cells that develop which would bring a threat for local flash flood concerns, similar to the past few days. The good news for today is the deeper moisture presence will be less pronounced, so seeing a downward trend in the potential overall. In any case, still enough for one more day of impacts lead to MRGL risk continuity from previous forecast. ....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 Southeast CONUS. Greatest opportunity will lie along the central Gulf coast where the proximity of the surface low and attendant surface trough could allow for short periods of convergence in-of areas along and south of I-10 from LA back into the FL panhandle. Guidance remains inconsistent on any organized convective placement with a smattering of heavy QPF bullseyes anywhere along the Gulf coast with even some extending back up through the GA and portions of the Carolina's. With PWATs remaining up inside the 90-99th percentile along the immediate coast and suitable instability presence, the previous MRGL was maintained with general continuity. ....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 lead to a period of convective development within the northern Sierra's through northern CA and southern OR. 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 easily produce local 0.5-1+" of precip in a short time. Given the favorable pattern into the terrain still dealing with remnant burn scars and complex drainage, the risk for at least isolated flash flooding still has merit. The previous MRGL risk was generally maintained with only minor adjustments. Kleebauer 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.=20 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).=20 Hurley ....Previous discussion... Disturbance across the Plains will move northeast into the Midwest and eventually the Great Lakes with heavy rain prospects carrying=20 through the region. This is marking the end of a persistent heavy=20 rain setup for the past several days with guidance indicating the=20 highest potential over IA, northern IL and southern WI. Ensemble=20 trends have shifted to places along and north of I-80 seeing the=20 greatest potential for 2+" of rainfall at any point in the D3=20 period, however there's still some uncertainty on specifics of=20 where the heaviest core of precip will occur when assessing=20 individual deterministic, so the current MRGL forecast was=20 sufficient for this time. That said, there's a good chance we will=20 see an upgrade at some point in the next series of updates, but=20 details will need to be ironed out on the previous periods of=20 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!4ixsgMmH1FB5anOejqfmAjYsIL4VzysAj6MinXbtUouE= Wa1DCsfr5ZkIsKlH4zMOP61WbZ7xwJ9T1EDn2lWjU7RWJ0Q$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4ixsgMmH1FB5anOejqfmAjYsIL4VzysAj6MinXbtUouE= Wa1DCsfr5ZkIsKlH4zMOP61WbZ7xwJ9T1EDn2lWj7DVtO_o$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4ixsgMmH1FB5anOejqfmAjYsIL4VzysAj6MinXbtUouE= Wa1DCsfr5ZkIsKlH4zMOP61WbZ7xwJ9T1EDn2lWjoKcJ-20$=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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