965 FOUS30 KWBC 300055 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 855 PM EDT Tue Sep 29 2026 Day 1 Valid 01Z Wed Sep 30 2026 - 12Z Wed Sep 30 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM THE SOUTHWEST INTO THE CENTRAL HIGH PLAINS... 01Z Update... The threat of flash flooding...with some localized considerable impacts...will continue throughout the overnight hours from the Southwester U.S. across the southern portions of the Rockies and out onto the adjacent central Plains. Radar and satellite trends from the late afternoon and early evening allowed for some of the outlook areas to be trimmed from the western extent. However...moisture with a subtropical connection remains in place with favorable upper flow pattern to maintain the threat. As the moisture emerges over the plains and interacts with an amplifying synoptic scale trough over the central portion of the country...shifted the axis of excessive rainfall threat southward to follow the trend first started in the 29/12Z suite of guidance, Otherwise...the changes to the on-going outlook were generally small. Introduced a Marginal Risk area over the southwestern Florida peninsula as an area of shower and thunderstorms approached the coastline as of 00Z along an inverted trough. Bann 16Z Update: The main premise of the forecast remains unchanged with a significant, widespread heavy rainfall threat across much of AZ/NM into portions of west TX as the tropical remnants of Polo make their way northward, contributing to a prominent flash flood prospect over the Desert Southwest into the Southern High Plains. 12z CAMs continue to pinpoint a significant heavy rain threat across southeastern AZ, including the Tuscon area where 2"/6-hr probabilities running >70% for much of the area, a threshold that typically verifies more substantial flash flood prospects in that area, historically. The environment across the Southwest remains ripe for heavy rainfall rates between 1-2"/hr and potential for widespread 2-4" totals, locally higher given the deep moisture profiles stemming from advection of Polo's moisture being pulled poleward. Latest 500mb analysis indicates the evolution we have been anticipating the last several forecast cycles as the mid-level energy from Hurricane Polo begins to interact and couple with the upper level low (ULL) currently positioned over the Colorado River basin out between AZ/CA/NV. Expectation is for the main energy from Polo to become fully incorporated into the ULL leading to the addition of stronger vorticity advection into the overall setup that will materialize over the course of the D1 and beyond. Time frames of note will include now through 00z across southeast AZ as the initial surge of convection will occur over the area with a quasi-linear band of heavy rainfall will initiate over eastern Pima county and slide east-northeast through the course of the afternoon. This will lead to widespread flash flood concerns over the I-19 corridor from the border to north of Tuscon with the complex of thunderstorms likely expanding east into impact areas along and north of I-10 into western NM. This area is where the signal is very prevalent for rainfall totals >3" with the latest 12z HREF blended mean QPF between 3-5" over the area just northeast of Tuscon into western NM with the maximum located within the Apache and Gila National Forests. Latest probabilities for >3" are substantial in that same area with the extension of 60-90+% probabilities all the way into Tuscon proper which enhances the threat of the locally significant flash flood concerns in the region. As we expand further east, the rest of NM will become inundated with widespread heavy rainfall late-afternoon through the overnight time frame with the heaviest rainfall positioned over the southern and eastern area of the state. Remnant moisture and vorticity advection being absorbed into the upper pattern will co-locate within the area from far west TX to points northeast leading to substantial convective coverage, as well as some organization trends that are conducive for more appreciable heavy rain footprints. The areas of concern will lie within the Upper Trans Pecos from Clines Corner down to the southeastern reaches of NM, including the more flash flood prone areas along the Pecos river (Roswell-Artesia-Carlsbad) where the combination of small stream and arroyo flooding and urbanization will likely provide an avenue for more locally significant flash flood prospects this evening as a prolific line of thunderstorms moves through the area. Latest 12z KEPZ RAOB this morning came in with PWATs of 1.55", a daily maximum already established for the date, and well beyond the 95th percentile for seasonal climatology. Current forecast is for PWATs to rise further, putting the region within historical thresholds when it comes to some of the higher PWAT readings in general. This type of environment typically precludes more substantial flash flood concerns, and this setup is no different. Expect the Eastern NM High Plains, Upper Trans Pecos, Sacramento Mountains, and adjacent West TX High Plains from the TX Panhandle into the Permian Basin to be under the threat of enhanced flash flood chances through the back half of D1, bleeding into D2. A targeted MDT was added over the AZ/UT for the central portions of the bordering area due to another round of convection occurring this afternoon under the influence of the ULL. Ongoing flooding over the area enhances sensitivities for the area with local FFG's basically as low as they could go before more flooding ensues. In coordination with the local SLC and FGZ WFO's, a MDT risk was added to target this specific area with an additional 1-2" of precipitation possible in any convection that occurs this afternoon. This threat will wane with the loss of diurnal heating around sunset. Broad SLGT risk continues over the Central Plains with a bit more of an isentropic pattern materializing across KS into NE/IA which will likely include some convective schemes, but less instability and a less robust deep moisture presence compared to areas of the Southwest will limit the threat to more scattered flash flood concerns this evening. 12z HREF EAS probabilities for >1" are still fairly robust (50-80%) over the area from nort-central KS up through the Missouri River Valley and adjacent Corn Belt areas of IA, but the >2" signal drops off considerably which notes a limit to the upper threshold of the forecast which curbs the threat closer to a SLGT for this period. Kleebauer Day 2 Valid 12Z Wed Sep 30 2026 - 12Z Thu Oct 01 2026 ...THERE ARE MODERATE RISKS OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS, AS WELL AS THE CORN BELT... ...Front Range to Southern Plains... 20Z Update: Maturing lee cyclone across the Central and Southern High Plains will allow for a continued heavy rain threat across the Sangre de Cristos into the San Juan Range as the flow shifts out of the northeast along the northwest periphery of the surface low, creating a textbook upslope flow regime to perpetuate the rainfall over the terrain of southern CO into northern NM. The prospects of flash flooding will be enhanced due to the antecedent moist soils brought about by prior periods of rainfall, some of which will likely cause flash flooding in their own right, leading to a heightened probability for flooding given the overlapping nature of heavy precip. 12z HREF continues to advocate for significant totals, 2-4" with locally higher, of additional precip within the mountains of the Southern Rockies into the Front Range as the combination of upslope flow and enhanced axis of deformation will lead to two primary periods of heavy precip; once in the morning and then once again in the evening as we see the surface low intensify and strong mid- level vorticity advection pivots around the ULL center. HREF probabilities, both EAS and neighborhood probabilities for >2" remain very high across the aforementioned area leading to high confidence of the heavy rain threat with multi-day totals likely breaching 3" over a large area over the Front Range of southeastern CO into northern NM. The previous MDT risk was maintained with little adjustment given the continued signal. Across the Southern Plains from Oklahoma down through Texas, the setup is more classic with regards to increasing low-level convergence along a propagating cold front that will materialize from the surface cyclogenesis over the High Plains. The flow will be fairly meridional ahead of the slow-moving mean trough/ULL moving through the Southwest U.S. creating a broad area of relatively backed flow across portions of west TX into the Red River Valley down through the Central Rio Grande Valley (RGV) and Edwards Plateau by Wednesday evening into early Thursday morning. Model consensus is for the initiation of heavy convection along the front as it migrates out of the High Plains of TX with the western periphery of precip likely developing from the western Rolling Plains down into the Lower Trans Pecos and adjacent Concho Valley by late Wednesday afternoon. This will set the stage for a broadening convective footprint over the Southern Plains as the warm sector environment with deep tropical moisture presence will interact with the frontal progression as it slowly moves eastward through the area Wednesday night. Models indicate a formidable 35-45kt LLJ structure situated from the RGV up into the Central Plains as the warm sector maturation will be well-defined with continued moisture advection poleward until the front passes over any given area. MLCAPE between 1500-2500 J/kg bisecting the eastern two-thirds of the region will offer plenty of instability to couple with 30-40kt Effective Bulk Shear, creating an environment conducive for stronger mesocyclone cores and merging multi-cell clusters that will provide heavy rain for a large area come Wednesday evening. HREF neighborhood probs for >3" are upwards of 60-90% over the area from the Lower Trans Pecos to the central Red River Valley between TX/OK with an average of 40-60% over the entire stretch from Eagle Pass, TX up towards Norman, OK. This is a substantial area of heightened probs for 3" with modest probs (25-50%) for >5" locally with the best signal over the Lower Trans Pecos and northern Hill Country between San Angelo and Fort Worth. This is more than sufficient for a continuation of the MDT risk with some adjustment to account for a bit slow forward propagation forecast on the northern edge of the line that should keep the worst of the rainfall just west of the DFW metroplex. This will be an area to keep watching over the next 24 hrs as the threat for more appreciable urban flooding in a scenario where the line makes headway into the metro. ...Central Plains into the Corn Belt... The maturing cyclone over the High Plains will lead to a progressive warm front on the eastern flank of the low with a general warm sector evolution occurring from the Southern Plains into the southern reaches of the Midwest. Rainfall from isentropic ascent will already be occurring on the northern periphery of the low, but limited instability will maintain more "subdued" rates that are coincident with more appreciable flash flood prospects. By Wednesday evening, that will no longer be the case as the warm front progression will open the door to a more favorable environment with modest instability development along and south of the front which is classic for these maturing lee cyclones. PWAT anomalies of +2 to +3 deviations will have advected into the region creating a formidable deep layer moisture profile to couple with the tall, skinny CAPE signatures expected over the Central Plains into northern MO and southern to central IA. As of this time, there is a strengthening consensus for heavy rainfall potential across northern KS into southeastern NE a strong shortwave ejection is anticipated on Wednesday evening with a budding LLJ occurring ahead of the trough located over the Rockies. Convection will breakout by Wednesday afternoon and expand northeastward into the Missouri River Valley and neighboring Corn Belt by Wednesday night with training convection within proximity of the warm front. Cells will develop across the warm sector and move northeast, in tandem which will eventually feed into the likely convective cluster migrating along the front from north- central KS into southern NE, eventually making headway into western and central IA after nightfall. The sufficiently buoyant environment and deep moisture presence will lead to hourly rainfall rates between 1-2"/hr in the strongest cell cores with some repeating action along the warm front. This has led to some robust signals in the deterministic CAMs and associated HREF blended mean QPF output which shows a general 2-4", locally as high as 6" over the course of Wednesday afternoon into early Thursday morning. The most notable area was that corridor from the KS/NE border up through Omaha over into Des Moines with a higher QPF footprint situated along and south of I-80. There will likely be a sharp cutoff in the greatest threat for flash flooding as north of the warm front will allow for a more stable environment and less of the threat of the higher rates coincident with flash flooding. 12z HREF FFG exceedance probabilities over 3hrs notes a maximum prob of 30-50% from Hastings over into Omaha and surrounding areas from 00-09z, aligning well with a prolonged 1"/hr or great rate forecast within that zone over the period of time in question. In coordination with several WFO's over the Central Plains and Midwest, a MDT risk was added for the new D2 update with highest confidence in that area between I-70 to I-80 over KS/NE/IA. Kleebauer Day 3 Valid 12Z Thu Oct 01 2026 - 12Z Fri Oct 02 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHERN PLAINS... 20Z Update: Little changes were necessary for the previous MDT risk issuance as the overall synoptic setup remains relatively unchanged. Expectation is for considerable rainfall to continue across south-central TX up through the DFW metroplex into Eastern OK on Thursday as the cold front slowly advances through the Southern Plains. The primary instability axis is positioned right across the Southern Plains into the the southern area of the Midwest within a broad warm sector that developed over the course of the prior 24 hrs into the new D3. Rainfall potential over the Hill Country is the most notable area for appreciable impacts as the Thursday afternoon and evening time frame could spell another period where 2-4", locally higher totals are plausible leading to locally significant flash flood prospects given the sensitivity of the area in general. PWATs over 2" with sufficient low-level buoyancy will create a suitable environment for heavy rainfall with rates likely between 1-2"/hr with as high as 3-4"/hr for intra-hour rate potential, a signature notorious for elevated flash flood concerns within the Hill Country and the I-35 corridor. This has led to a maintenance of the MDT risk over the area, expanding northward into portions of eastern OK. The area further north into IA/IL/MO will be another area to monitor closely as the prolonged diffluent flow over the Plains into the Midwest will leave the door open for more heavy rainfall over a broad area of uncharacteristically high PWATs thanks to an airmass coincident with the remnants of Tropical Cyclone Polo. PWATs between 2-2.25" over the Midwest and Mid-Mississippi Valley will be upwards of 3-4 standard deviations above normal, an anomaly that will likely flirt with some of the daily and even monthly maxima for PWATs over this general area as noted via the NAEFS anomaly percentiles. A broad SLGT risk with high-end SLGT forecast over the area just west of Chicago back down through the east- central Plains and Mid-Mississippi area of MO will be a focal point for convection and scattered to potentially widespread flash flooding concerns by Thursday afternoon and evening. This area will be assessed in future updates for possible upgrades. Kleebauer ..Previous Discussion.. During this period a postively-titled upper level trough is expected to weaken, then stall over the Central and Southern Plains. Along the surface frontal boundaries heavy rainfall will persist with potentially numerous instances of flash flooding for the Southern Plains. A Moderate Risk was maintained southeast Oklahoma to the Texas Hill Country and South Texas where large- scale ascent afforded in part by favorable upper jet forcing will continue to interact with an axis of anomalous moisture (2-2.25+ inch PWs). This multiple day event will have possible overlap, thus keeping an elevated risk for flooding. A broad Slight Risk extending north from Texas to Wisconsin and northern Indiana and then west to eastern Colorado. While areal average rainfall amounts are expected to be less in this region, moisture drawn north and focusing ahead of a cold front settling south across the region is likely to fuel the potential for widespread moderate to localized heavy rainfall, resulting in at least isolated runoff concerns. Campbell/Pereira Day 4 and Day 5 Valid 12Z Fri Oct 02 2026 - 12Z Sun Oct 04 2026 ...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTHERN TEXAS ON DAY 4 AND FROM THE CENTRAL GULF COAST INTO THE TENNESSEE VALLEY ON DAY 5... 2030Z Update... Deterministic and ensemble guidance maintained decent run to run continuity that resulted in few changes needed to the previously issued Excessive Rainfall Outlook on either Day 4 or Day 5. The large scale picture still features deep moisture streaming northward from the Gulf of American into place ahead of a large scale mid-latitude trough digging south- and east-ward, Spaghetti plots from the EC ensembles suggested expanding the outlook areas westward a bit...moreso on Day 4. But the change does not reflect a fundamental shift in forecast reasoning. Bann Previous Outlook Discussion... Day 4... Mid-level energy associated with the trough moving into the central and southern Plains on Thursday will remain over the region into at least the early part of the weekend. Deep moisture will remain as well over parts of the southern Plains -- maintained by backing low level winds tapping Gulf moisture and drawing it westward into a lingering low level boundary. As this moisture interacts with the slow-moving mid-level energy that is forecast to remain over the area, there will continue to be some potential for heavy rainfall producing storms, impacting some areas that are likely to be left vulnerable to excessive runoff by the previous day(s) heavy rains. While forecast confidence has diminished some, there remained enough of a signal in the overnight guidance that showed additional heavy accumulations centered across parts of South to South-Cental Texas to maintain a Slight Risk over the region. Farther north and east, a cold front will continue to settle southeast through the Ohio Valley, with some potential for heavy rain along and ahead of the boundary. Supported by deep southerly flow along the western extent of the subtropical ridge, guidance continues to show a broadening pool of anomalous moisture spreading from the Gulf Coast into this boundary. Mid-level energy embedded within the flow may help produce areas of heavy rain, with some guidance indicating heavy amounts along the Gulf Coast from Mississippi to the Florida Panhandle this period. Day 5... Moisture will continue to deepen from the Gulf Coast northward into the Tennessee Valley -- with PW anomalies increasing to 2-3 std dev above normal across much of the region during this period. A Slight Risk was drawn along the axis of deepest moisture (PWs at or above 2.25 inches) which is expected to extend from the central Gulf Coast northward into an area of enhanced ascent centered in the vicinity of the Tennessee Valley. The previously noted front dropping south into the area along with mid-level energy emanating from the Plains are expected to help focus heavy rainfall development over this region. Forecast confidence was limited in part by model spread regarding the placement of the front, which is likely to play a role in where the heaviest amounts occur. Therefore, notable adjustments to at least the northern extent of the Slight Risk may be required in future updates. Pereira Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt $$