FOUS30 KWBC 262142 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 542 PM EDT Sun Apr 26 2026 Day 1 Valid 2131Z Mon Apr 27 2026 - 12Z Mon Apr 27 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN THE CENTRAL PLAINS... ...2139Z Special Update... Given trends seen in short term radar and satellite imagery about where convection initiated and its movement east-southeastward into better instability and inflow...amended the previous Excessive Rainfall Outlook by expanding the Slight Risk area deeper into Missouri. By doing that...there was better overlap with the HRRR guidance that has shown growing areal coverage and rainfall amounts. Given the run to run variability...confidence not strong enough to expand farther south and east but it may become clearer by the 01Z Update. MPD 0135 was valid for portions of the area through 27/0258Z. Bann ...16Z Update... Few changes were needed to the inherited ERO risk areas across the Central Plains for today and tonight. The high resolution CAMs guidance has generally remained set on far northeast Kansas and northwestern Missouri for the greatest likelihood of seeing training storms with a developing MCS this evening into tonight. That said, the details of exactly where the heaviest rains occur remains highly uncertain, with each CAMs model showing a different outcome. While unusual, considering the fast-evolving nature of most MCSs and the fact that this one has yet to develop, it's not surprising to still have this much uncertainty less than 12 hours out. Nonetheless, some of the guidance shows the heaviest rains focused in Nebraska and Iowa, while others focus much further south into the Kansas City metro. Thus, the ongoing ERO risk areas still highlight the "middle ground" of the guidance. Users should note that due to the high uncertainty, that significant changes may be needed once the storms start to fire later today, both in the upgrade direction along the swath of heaviest rains and training storms, and also in the downgrade direction in the areas where it becomes clear little to no rain will occur. A small north and west expansion was made to the Slight Risk area into Nebraska and Kansas with this update, reflecting a plurality of the CAMs guidance focusing the heaviest rains a bit more to the north and west. Meanwhile the Marginal was expanded a bit to the south in Kansas and Missouri to reflect the typical southward drift in the guidance when depicting convective development, and to reflect some of the uncertainty with the southward-favoring guidance, such as the HRRR. The Marginal was also expanded northeast into northeastern Iowa with the latest 12Z HREF suite highlighting potential FFG exceedance after midnight tonight. Further, the 12Z HREF suite highlighted a portion of Arkansas for a thunderstorm cell or two moving southeast through a more hydrologically sensitive area, so the Marginal was expanded there as well. Wegman ...Previous Discussion... The latest hi-res model guidance has trended substantially toward a corridor of heavy rainfall in the Central Plains this evening and tonight. Therefore, confidence has increased in a heavy rain event, but considerable uncertainty still remains on the location. Some guidance places the heaviest rain almost wholly into Iowa, while other guidance is further south in the vicinity of the I-70 corridor in Kansas and Missouri -- almost 200 miles of variability with approximately 18 hours of lead time. Given the consistent signal for significant rainfall, we have upgraded to a Slight Risk, and drawn it broadly to account for positional uncertainty. The contours were largely based on EAS probabilities from the 00Z HREF; and the major axis of the Slight Risk area intersects the QPF maximum on the AI versions of the GFS and GEFS. Convection is expected to develop this afternoon on the nose of a strengthening low-level jet (LLJ) and plume of instability, likely in northern Kansas or southeast Nebraska initially. The convective evolution in the approx. 6 hours after initiation will be important. In general, all models show a west-to-east progression of thunderstorm clusters, consistent with the bulk shear vectors, and along a focused area of low-level convergence near the nose of the LLJ. Some models show scattered clusters progressing over similar areas, but with intermittent breaks and not precise training; others show a more continuous band of convection training in a specific corridor (sustaining 1-2 inch per hour rain rates for several hours in a given location). Comparing QPFs from those scenarios suggests the latter scenario could double rainfall, with amounts potentially high enough to lead to significant flash flooding. Therefore, this will need to be monitored closely. A Marginal Risk was considered in the Arklatex region as ongoing convection will likely persist in some form beyond 12Z. However, a squall line in southern Arkansas appears to be forward propagating and accelerating, if anything. And other thunderstorm activity is more isolated and generally less intense. Therefore, a non-zero excessive rainfall risk does exist in the region, but no Marginal Risk was outlined at this time. Lamers Day 2 Valid 12Z Mon Apr 27 2026 - 12Z Tue Apr 28 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MIDWEST... ...2030Z Update... The inherited Slight Risk was shifted well to the south and east with this update, to include most of Illinois, Indiana, and a portion of western and central Kentucky. While many of these areas have been very dry lately, a stream of deep Gulf moisture will advect north into the area on and LLJ featuring 60+ kt winds at 850 mb and PWATs potentially exceeding 1.75 inches in the Slight Risk area Monday night. MUCAPE values anywhere from 1,500 to 2,500 J/kg is plenty of needed instability to support storms growing to heights capable of producing heavy rain. Thus, while any severe storms may be progressive in the form of a line over portions of this area, that kind of moisture, any trailing segments, and the antecedent dry soils could work to increase the flash flooding risk. Anywhere soils have hardened due to the recent drought will make the onset of heavy rain convert nearly all of the rain to runoff. Some of the guidance, especially the HRRR, shows that late tonight, the southern end of the line across Tennessee may hang up due to the strength of the LLJ pushing against the southward progressing line of storms. Then on the northern end, from Chicago north, areas north of the greatest eastward progression of the storms will also have a greater chance of hanging up and training from southwest to northeast. The greatest threat of flash flooding will be in urban areas of the Slight risk such as Chicago, Indianapolis, and St. Louis. The Slight Risk may need to be expanded further south across Tennessee to include Nashville and Memphis if the front progresses faster than expected. Otherwise, the Slight Risk for Day 3 for that region covers expected lingering convection in Tennessee and points south into Tuesday morning. Across Minnesota and Wisconsin, the Marginal Risk was expanded in coordination with DLH/Duluth, MN forecast office. Recent heavy rains across the upper Midwest have left soils more vulnerable to flash flooding, despite less intense rainfall expected due to lack of instability. Wegman ...Previous Discussion... The training band of convection from Sunday Night is likely to progress eastward into the Midwest on Monday; placement uncertainties grow on Day 2, but there has been a general southward shift in the location of the heaviest rainfall in model guidance over the last couple cycles. Some guidance now shows the corridor of heaviest rainfall on Monday and Monday Night as far south as the I-70 corridor from St. Louis to Indianapolis, while other guidance remains closer to the Illinois-Wisconsin border, where the existing Slight Risk area was concentrated. This is about a 200 mile spread. So while heavy rainfall is expected, confidence remains somewhat low on the location. Given the overall trends, the main change was to shift the axis of the Slight Risk southward, albeit only about 70 miles out of deference to continuity. The overall environment will be very supportive of heavy rain rates. A plume of 1.2 to 1.7 inch PWs (above the 95th percentile for late April) and moderate to strong instability will support 1 to 2 inch rain rates in organized convective clusters and lines. Although training convection may continue into Monday morning, convective lines should become oriented more in a north-south fashion later in the day as forcing along an accelerating cold front increases. The best opportunity for training convection, and therefore a longer duration of heavy rain rates, should be in or near the Slight Risk area. Areas further south should not only see steady progression to any convective lines, but have also been much drier lately, so the risk of flash flooding is lower despite some similar QPF from the latest model guidance. Lamers Day 3 Valid 12Z Tue Apr 28 2026 - 12Z Wed Apr 29 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MID-SOUTH... ...2030Z Update... A weak area of low pressure, forming on a jet streak and rather weak upper level shortwave in the upper levels, and downwind of a pressure ridge of cooler air over Oklahoma, will push east across the Mid-South on Tuesday. As it moves, it will run into a plume of deep Gulf moisture across Texas and the mid-South. The uplift of the cooler air, upper level support, deep moisture and instability, will lead to robust thunderstorm formation across Arkansas and far northern Louisiana. The storms associated with this front will merge with a stalled front that led to shower and thunderstorm formation further north on Monday. This line of storms is likely to form in northern Arkansas, then push south across western Tennessee, northern Mississippi, and northern Alabama. The merger of these two lines of storms and their associated fronts will likely result in areas of training along the frontal interface. Deep Gulf moisture supported by a 30-40 kt low level jet will support backbuilding and further thunderstorm development behind the leading line of storms. PWATs could approach 2 inches in some areas. Hydrologically, western Tennessee especially has been very dry with surface soil moisture levels less than 2% of normal. While for most areas this will likely help mitigate any flooding concerns, the potential for training storms capable of rainfall rates to 3 inches per hour will likely overwhelm local drainage basins where those rates can materialize, regardless of the prior dry conditions. Thus, a Slight Risk upgrade was hoisted to account for the very favorable meteorology (strong storms capable of multiple inch/hour rates, training, and a steady supply of deep tropical Gulf moisture), which can overcome very unfavorable hydrology. Flash flooding is most likely where ever these heavy rainfall rates occur over urban or more flood sensitive areas. Further south into Mississippi, more recent rainfall has made a few areas have above normal soil moisture levels for this time of year, with many areas around or slightly below normal. Wegman 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