FOUS30 KWBC 121938 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 338 PM EDT Sun Apr 12 2026 Day 1 Valid 16Z Sun Apr 12 2026 - 12Z Mon Apr 13 2026 ...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF CENTRAL AND SOUTHEAST TEXAS... ...Texas... 16Z Update: Conditions for a localized area of significant rainfall are increasing as of the latest 12z CAMs and associated hi-res ensemble with a QPF maxima positioned across the I-35 and points just east to the I-45 corridor in eastern TX. Current radar analysis shows a progressive line of thunderstorms migrating eastward with a weakening disposition as of the last 30 minutes. This set of storms will fade over the next few hours with a secondary batch of cells likely to materialize to the southwest across the I-35 corridor between Killeen to Austin on the edge of a remnant cold pool from the aforementioned storms. Areal MUCAPE will increase given favored diurnal instability leading to a widespread area of 1000-2000 J/kg situated across the I-35 corridor and points east with 2000-2500 a bit further back into Hill Country which will lie within the western flank of any expected convective development. Environmental parameters of shear and instability along with a remnant cold pool will act as a favored initiation point this afternoon with multi-cell modes and cold pool mergers likely to enhance a more organized convective cluster across east- central TX. This first batch will have the ability to drop appreciable amounts of rainfall with some of the CAMs insistent on QPF maxima between 3-5" on the first round of convective development with hourly rates between 1-3"/hr in the stronger cell cores. Despite the drier antecedent conditions in place, the overall hourly rates confined within a narrow corridor would be sufficient to induce some isolated to widely scattered flash flood signals within a region that is prone to flash flooding due to the complexity of terrain and unfavorable limestone bases that promote high run off capabilities. The real concern is what is being depicted in the evening as another batch of thunderstorms is forecast to materialize within the southern edge of a remnant cold pool from prior convection, coupling with a weak LLJ developing across east TX after 00z. The convergence pattern is well-documented across the area between I-35 to I-45 with a general overlapping in that zone from the latest CAMs. Neighborhood probabilities for >5" total in the D1 period have escalated to 30-45% across the above zone with a bullseye centered between Austin/Brenham/San Marcos. Where this overlap occurs with the previous round of convection, locally significant flash flooding will be plausible considering the priming and totals being represented in the means. HREF blended mean QPF is solidly above 4" for multiple areas between the two major TX interstates with some 5" pixels showing up over those areas east of I-35. The SLGT risk in place has been expanded a bit further south to account for these trends with the risk likely leaning towards the higher end of the threshold. If the setup gains near term traction, a targeted upgrade to a higher risk is not out of the question, so this one will bear watching. Kleebauer ...Great Lakes... 16Z Update: The MRGL risk remains in effect across northern MI, but was expanded further west-northwest into the MI U.P. and northern WI to adjust for the latest trends and observations of ongoing rainfall and minor flooding taking shape in these areas. Secondary batch of elevated convection migrating northeast out of MN/southwestern WI will entice more localized hydrologic concerns over the area where the coupling of snow melt and moderate to heavy rainfall will enhance flooding of rivers and streams littered across the northern Great Lakes. Some flood reports are trickling in across the area already, so want to cover bases with a low-end flash flood threat to mingle with the river flood prospects as multiple rounds of convection are anticipated through the period. The next batch will drive up from the south as a weak shortwave enters from the central Midwest and provides another period of convectively driven rainfall from south to north beginning in IA/IL and moving northeast impacting parts of the Door Peninsula into the northern mitt of MI. Kleebauer ..Previous Discussion.. A Marginal Risk remains in effect for this period. Anomalous Gulf moisture pumping northward will interact with the draped frontal boundary to bring enhanced rainfall to the region. NAEFS continue to show PWs and IVT values that are above the 99th climatological percentile that features a combination of saturated soils and lingering snowpack. Accumulations of 1 to 2 inches are anticipated for the northern half of Mitten which may cause any lingering snowpack to melt and possibly exacerbate the flooding potential on Sunday. Campbell/Mullinax Day 2 Valid 12Z Mon Apr 13 2026 - 12Z Tue Apr 14 2026 ...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE UPPER MISSISSIPPI VALLEY AND UPPER GREAT LAKES REGION... 20Z Update: Little change was necessary to the inherited MRGL risk across the Upper Midwest and Great Lakes. High neighborhood probs (60-90%) for >1" totals across the region coupled with rapid snow melt over the U.P. and northern WI should enhance hydrologic concerns for the period. Minor flooding occurring in D1 will generally continue through D2 as another round of convection will impact the area from eastern MN through the northern half of MI. There's some elevated probabilities for rates exceeding 1"/hr across portions of WI tomorrow evening as a formidable LLJ and increasing convergence within a progressing warm front could very well maximize the potential for heavier precip. This would be the most notable location for the setup, but the setup is relatively short- lived, so did not feel an upgrade was necessary. Kleebauer ..Previous Discussion.. Another round of showers and thunderstorms will move through the Upper Mississippi Valley and Great Lakes during the afternoon and evening hours, prolonging the threat for excessive rainfall, increased snow melt and flash flooding. A Marginal Risk remains in effect from eastern Minnesota to northern Michigan. Campbell Day 3 Valid 12Z Tue Apr 14 2026 - 12Z Wed Apr 15 2026 ...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FROM THE TEXAS HILL COUNTRY TO THE UPPER MIDWEST/GREAT LAKES REGION... 20Z Update: The broad MRGL risk for D3 was generally maintained with multiple areas likely to see convective activity during the period. The main area of focus will likely occur over the Midwest as increasing diffluent axis downstream of a deep western trough will enter the area with convective development likely to occur over IA and motion to the east-northeast. A developing upper jet coupling will likely aid in regional ascent with fairly generous instability axis situated from the Corn Belt to the southern Great Lakes and points south. Models are in agreement on there being a solid precip footprint, but they are all over the place in regards to the placement. In any case, there was still some time to review with the CAMs guidance coming into the picture by tomorrow, so will wait to see if there will be another upgrade potential with this setup, which is leaning more towards a necessity considering the above synoptic and thermodynamic variables. Kleebauer ..Previous Discussion.. Multiple rounds of strong to severe thunderstorms expected from Texas to the Midwest states, given favorable wind shear and instability in place as multiple impulses eject across the Plains. Gulf moisture will be funneling northward between the trough over the Rockies and the ridge over the eastern states. The environment will be favorable for a few mesoscale convective systems to develop and the limited eastward progression will likely result in areas that have excessive rainfall leading to some instances of flash flooding. A Marginal Risk area span from the Texas Hill Country northeastward to the Midwest and western Great Lakes. Campbell 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