Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jun 23 2025 15:58:41 FOUS30 KWBC 231555 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1155 AM EDT Mon Jun 23 2025 Day 1 Valid 16Z Mon Jun 23 2025 - 12Z Tue Jun 24 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF NEW MEXICO AND WEST TEXAS, AND FROM KANSAS INTO SOUTHERN=20 WISCONSIN... 16Z Excessive Rainfall Discussion Update... Based on the 06Z neighborhood probabilities...and a quick look at the probabilities from the 12Z run...extended the Slight Risk area a bit to the east to cover more of southern Wisconsin. In the=20 broader picture...the risk of excessive rainfall exists on the=20 periphery of a broad upper level ridge from New Mexico and West=20 Texas...across the Central Plains into the Upper Midwest given the=20 persistent deep-layer advection and embedded shortwave energy. The=20 12Z HREF probabilities aligned well with the previously issued=20 Excessive Rainfall Outlook and only minor adjustments were needed. Bann=20 ....New Mexico into West Texas... A general pattern of persistence will maintain a relevant posture for scattered to widespread convective impacts across Southwestern TX up through the eastern half of NM with the highest potential impacts aligned within the terrain. Ample moisture advection provided by prevailing southerly-oriented flow within the sfc-500mb layer will correlate with an environment capable of locally heavy rainfall within any cell maturation across the above areas. The proxy of the deep layer moisture and RER jet dynamics from the mean trough situated to the west will create an accumulated risk of showers and storms propagating over the same areas leading to increasingly compromised soils, or even interacting with the already prevalent burn scars situated over the Sacramento Mtns. Storm motions will likely be fairly weak as noted by the forecast Corfidi vectors residing between 5-15kts on average within the confines of the entire Southwest TX and Southeast NM domains. This will allow for modest training concerns that will ultimately cause problems if they fall within any of the urban centers along the Upper Trans Pecos out into the complex topography located in the region. The best chance for flash flooding will likely be within those burn scar locations where hydrophobic soils are still a problem and can promote a formidable runoff regime that could cause significant problems locally if a heavy cell forms overhead. Areas within the Pecos river are also notorious for flash flooding capabilities due to the limited drainage structures prevalent within town limits. Considering the HREF neighborhood probs for >2" are running between 50-90% over a large area extending from the Davis Mtns up through the Eastern NM Caprock, the previous SLGT risk was upheld with wording of a higher end SLGT considering the environment in place. ....Central Plains to Midwest... The Central Plains through the Midwest continues to lie within the northern and northwest periphery of a broad ridge extension centered over the Mid Atlantic. The proxy of the ridge has allowed for a persistent south to southwesterly mean flow within the column leading to steady moisture advection within the boundary layer up to around 500mb. Current PWATs from 00z RAOB analysis across the Plains and Mississippi Valley denote moisture anomalies that are approaching +2 deviations, something that has also been reflected in the last several days of NAEFS anomalies within the ensemble suite. The relevant moisture pooling across the zone extending from KS up into the Midwest will lead to a formidable widespread convective initiation scheme that will develop due to increased convergence along and ahead of a slow-moving cold front nosing down through the Northern Plains. The interaction of the cold front with a very buoyant environment (MUCAPE 2500-4000 J/kg) located across the Central Plains up into the Upper Mississippi Valley will create a broad axis of heavy convection with the heaviest precip likely correlated with the 2+" PWAT domain located from North-Central KS and points northeast into IA. There's a general consensus within the latest CAMs suite of significant totals between 2-4" forecast located within the aforementioned zone, including some deterministic output and lower neighborhood prob correlation for some places exceeding 5". The prospects for those types of totals stems from not only the favorable deep moist convective pattern, but also the mean layer flow and surface convergence regime along the front creating a favorable environment for back-building convection and training cell prospects. This is fairly well-documented when assessing forecast Corfidi Vectors continuing this divergent storm motion setup within the upshear and downshear calculations given the forecast wind field(s). A strong RER jet dynamic will only aid in a blossoming QPF field and maintenance as the mean flow takes the convective pattern off to the northeast. This pattern will carry through Monday evening into early Tuesday morning with some weakening of the convective field anticipated due to loss of diurnal destabilization. In any case, this setup is capable of widespread 1-2" totals with the hardest hit locations likely seeing 2-4" with locally higher as noted in the latest CAMs. The saving grace, at least initially for D1, are the drier soils centered over the Central Plains into parts of Southeast NE and Southwest IA leading to higher FFG indices that will need some priming in order to likely reflect a more significant flash flood response. The change from the previous forecast was an adjustment to the south with the overall SLGT risk as guidance reflects a bit of a faster frontal progression than anticipated. This places a higher risk a bit south over Northeast KS to points northeast. The threat for locally heavy rainfall is also forecast across Southwest KS with cells ejecting out of the High Plains of CO/NM, but CAMs are less defined due to the lack of a boundary layer focus comparatively. The MRGL exists in at particular area, but if CAMs come into agreement on a local max centered near or southwest of DDC, then the SLGT risk may be extended further to the southwest to account for the prospect. Kleebauer Day 2 Valid 12Z Tue Jun 24 2025 - 12Z Wed Jun 25 2025 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF CENTRAL NEW MEXICO... ....New Mexico... Upper level pattern will be in a short transitory phase, but one that will ultimately lead to a threat of prolonged heavy rainfall from training convection across much of the terrain in Southern and Central NM. The massive ridge to the east will flex further as we head into Tuesday with the higher heights on the western fringes pushing back west beyond the eastern portions NM. A steady north- south progression within the mid and upper levels will send numerous smaller shortwave perturbations poleward with anticipated motions into the Sacramento's, eventually north into the Sangre de Cristos by the late-afternoon and evening period on Tuesday. Moisture remaining parked over the region coupled with the focused ascent and narrow upslope proxy within the Sacramento Mtns. will lead to a corridor of heavy convection remaining situated in-of the terrain. There's a growing consensus within all deterministic that local topographic effects within this pattern will yield some significant rainfall potential over areas that are prone to flash flooding, especially with the burn scars still present near Ruidoso creating higher runoff capabilities. 00z HREF depicted between 2-3" of rainfall in just the 12-hr period between 12-00z on Tue/Wed with precip continuing at the end of the run. Ensemble mean forecast within the NWP suite was up around 3" for multiple locations with a large areal coverage of at least 2" within the mean output. These are generally signals that favor not only flash flooding prospects, but widespread flash flood concerns with more significant impacts possible. The signal for heavy rainfall continues all the way up into the Sangre de Cristos where the afternoon and evening time frames call for widespread heavy thunderstorm activity aligned with the ridges of the southern Rockies. These areas also have burn scar prevalence that could exacerbate flash flood risks as runoff capabilities are maximized. Considering the anticipated threat bleeding further north within the guidance this evening, the previous MDT risk was expanded northward to encompass those areas within the Sangre de Cristos and neighboring valleys. The threat for a targeted higher risk over the Sacramento's is plausible if this signal remains for another forecast cycle or two. As of now, it is deemed closer to a high-end MDT risk with the area across the northern Sacramento's the most susceptible to significant impact potential. ....Central Plains to Midwest... The pattern across the Plains and Midwest that will bring heavy rainfall to those areas Monday night into Tuesday morning will bleed over into the D2 period with ongoing precip likely across Northeast KS into adjacent areas of NE/MO/IA. Flash flooding concerns will be ongoing at this time and recent CAMs output is signaling more rainfall through at least 18z will continue to plague those same areas. 00z HREF neighborhood probs over the 12hr period between 12-00z Tue/Wed denote a 40-60% chance of exceeding 2" over areas that will have already seen significant (2-4+") rainfall the period prior. Rates ~1"/hr are modest within the hi- res ensemble probability fields as well, a testament to the persistence in the heavy convective setup in place. There will finally be less of a concern late in the afternoon as the frontal progression migrates north the second half of the period, so the threat will likely be more focused in that area the first half of the forecast. Still, this is enough for a continued SLGT risk with higher end risk potential given the period overlap. The setup the following evening becomes trickier as the entire evolution comes down to the handling of the mid-level energy riding northeast out of the Southern Plains into the Central Plains and Upper Midwest after nightfall. Surface front from the prior period will eventually hit a roadblock on its southern progression and flip back to a warm front as it migrates back to the north under the guide of a potent LLJ generation across the Plains. The interaction between the front and the energy will create a secondary convective enhancement that will impact areas further north than the previous 36 hrs. The lack of overlap may inhibit significant impacts, however the training threat within the confines of the boundary may be enough to warrant some higher risk of flash flooding. The setup is depicted by guidance in the 00-12z period Wednesday, but position of the heaviest precip is seemingly all over the place. The threat is certainly there for 2-4" with locally higher, but specifics still remain sort of muddled. The SLGT risk prior was adjusted to reflect the ensemble mean QPF distribution with a heavy precip footprint still located over far Southeast SD into Southern MN for the period. How far north the front migrates and handling of the shortwave ejection will determine exactly where the heaviest precip will occur. Right now, anywhere within the SLGT risk is fair game, so it's a time frame to monitor closely. Kleebauer Day 3 Valid 12Z Wed Jun 25 2025 - 12Z Thu Jun 26 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF NEW MEXICO, CENTRAL PLAINS AND MIDWEST... ....New Mexico... Unlike the prior periods, the D3 is finally the downward trend to the incessant nature of scattered to numerous thunderstorms that will plague the state, especially across the Sacramento's and Sangre de Cristos. Despite the lower coverage anticipated, scattered thunderstorms are still plausible in the afternoon as ample heating during prime destabilization window (16-21z) will yield another threat of thunderstorms across the terrain and adjacent valleys. Current signals are nowhere near as robust as the D1/D2 time frames, but with potentially significant impacts prior, there's a greater threat of truly compromised FFG's leading in allowing for the bar to be very low for flash flooding. As of now, the ensemble mean is still highlighting the Sacramento's up into the I-40 corridor as the main areas of concern. A SLGT risk was maintained and expanded a bit to encompass the zones of greatest risk for flash flooding. A targeted higher risk is not out of the question for the Sacramento's, but will assess in later forecasts as we monitor how everything evolves leading into the D3. ....Central Plains to Midwest... Unlike the prior period where there is some uncertainty in the handling of shortwave energy and frontal positioning, there's a pretty good consensus brewing on the pattern converging in-of the Upper Midwest with sights on MN into Western WI as the evolution in D2 carries over into D3. Mean QPF output via ensembles is running between 2-4" for an areal average with the maxima positioned across Southern MN back into adjacent areas of SD/NE to the southwest. Not one, but two waves of convection will encroach the area with some spots potentially seeing some significant rainfall (>2") in both waves which will likely lead to scattered, bordering widespread flash flood prospects due to the compounding rainfall forecast. NBM 90th percentile QPF is well over 2" across much of the aforementioned region with some higher totals even extending back through NE. As of now, it's still a bit early for the higher risks due to some uncertainty the day prior which could shift the forecast a bit in either direction (north or south). For now, maintained a higher end SLGT across a large portion of the Upper Midwest with the eastern extension pushing all the way out into Northern WI. A targeted higher risk is certainly in the cards if this signal remains and consensus grows on the evolution of the synoptic details. Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6JDWsoDq-nw6xZhT08bInUtdTgQ54EjEt4NwY5wN7IXN= K1CvSe3imFDCi1GbGliq-ClWmRa3Kn7CMCMBRz_UZiOkh6w$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6JDWsoDq-nw6xZhT08bInUtdTgQ54EjEt4NwY5wN7IXN= K1CvSe3imFDCi1GbGliq-ClWmRa3Kn7CMCMBRz_UrApAAvQ$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6JDWsoDq-nw6xZhT08bInUtdTgQ54EjEt4NwY5wN7IXN= K1CvSe3imFDCi1GbGliq-ClWmRa3Kn7CMCMBRz_UFcyG5e8$=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) .