512 FOUS30 KWBC 040827 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 427 AM EDT Sat Apr 4 2026 Day 1 Valid 12Z Sat Apr 04 2026 - 12Z Sun Apr 05 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE ARKLATEX/LOWER MISSISSIPPI VALLEY AND A PORTION OF THE SOUTHERN GREAT LAKES... Much of convective evolution today depends on details about how much convection lingers and exactly where the convection is located this morning across Arkansas and Texas. East-northeastward progression of a mid-level wave toward the Great Lakes will aid in southeastward movement of a cold front into the ARKLATEX and Lower Mississippi Valley Eventually, the front will oriented more parallel to weakening flow aloft supporting additional opportunities for training convection as storms organize along remnant outflows and backbuild, with the potential for areal average rainfall in the 1-2" range leading to isolated instances of flash flooding. Maintained the Slight Risk area over portions of Texas and Arkansas ahead of convection moving out of Oklahoma and northern Texas from overnight prior of the start of the Day 1 period at 12Z Saturday. Surface analysis showed a wave of low pressure along the front in northeast Texas will also help to maintain/enhance the development of this convection as well as briefly slow the progression of the front northeast through the ArkLaTex, allowing for heavier rainfall totals as storms persist over the region for a longer amount of time before the front begins to sweep southward faster later into the afternoon. Also maintained the separate Slight Risk area to the east over portions of the Lower Mississippi Valley later today as moist southerly flow from the Gulf taps a pool of ~70 degree dewpoints and draws that airmass northward. These high dewpoints along with daytime heating will lead to a region of 1000-2000 J/KG CAPE supporting the development of heavy- rainfall producing thunderstorms ahead of the front. The combination of this initial development in addition to a second round of storms expected along the front with similarly high rain rates of ~2" per hour will also lead to the potential of locally heavier totals in the 3-4" range. While dry antecedent conditions/high FFGs may limit the overall threat, the potential for these higher rain rates/totals within the highlighted Slight Risks should be sufficient enough for at least a localized/urban scattered flash flood threat. Farther north, introduced a Slight risk area over portions of northern Ohio and northern Indiana due to a combination of locally heavy rainfall overnight falling on areas where the 1-hour flash flood guidance was locally as low as 1 inch and the approach of a front from the west which will potentially act to focus another round of showers and thunderstorms. Rainfall rates are not likely to be all that impressive nor will the duration of the rainfall be particularly long due to the progressive nature of the front and the strengthening flow aloft. Even so...recent rainfall has made the area more susceptible to problems with flooding and run-off. Bann Day 2 Valid 12Z Sun Apr 05 2026 - 12Z Mon Apr 06 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTH TEXAS ON SUNDAY... Much like model runs over the past day or two...the suite of numerical guidance from 04/00Z has continued to trend a bit faster with the arrival of a cold front from the north. This adds to the concern that moisture and instability will be swept out of the area very early in the Day 2 period...if not before the period begins at 12Z on Sunday. Spaghetti plots of QPF continue to show enough members with post-frontal amounts in the 1 inch to 2 inch range to keep the Marginal in place...but the area continued to be increasing confined to coastal areas and the deep south portion of Texas. Bann Day 3 Valid 12Z Mon Apr 06 2026 - 12Z Tue Apr 07 2026 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Bann 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