Subj : HVYRAIN: Excess Rain D2-3 To : All From : Mike Powell Date : Thu Jul 24 2025 08:37:53 FOUS30 KWBC 240804 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 404 AM EDT Thu Jul 24 2025 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... 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... 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 $$ --- SBBSecho 3.28-Linux * Origin: ILink: CCO - capitolcityonline.net (454:3/105) .