974 FOUS30 KWBC 040044 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 744 PM EST Tue Mar 3 2026 Day 1 Valid 01Z Wed Mar 04 2026 - 12Z Wed Mar 04 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MIDWEST AND OHIO VALLEY... Showers and thunderstorms are showing increasing vigor near and downstream of an instability pool near northern MO/IL border, with occasional bouts of training near Indianapolis IN at the present time. MUCAPE values are 500-1500 J/kg presently across much of MO into central IL, with some signs of recently of some southward sag. This has been supporting the elevated convection. This northern instability pool fades early, with recent RAP forecasts indicating a better instability pool near southern MO by morning after the low-level jet ramps up. This fits the idea of convection sagging southward with time, which is eventually supported by the forward propagation vectors, is parallel to the instability gradient, and parallel to the 1000-500 hPa thickness field. Hourly rain amounts up to 2" have been estimated by radar imagery lately, which seems a reasonable maximum for the overnight period. Should there be a couple hours of training, local totals to 4" would be possible. The three hourly flash flood guidance is relatively low, in the 1.5-2" range, partially due to the moderate to heavy rainfall that has occurred over the previous 12-24 hours. With more rain coming, believe the threat level is a higher end Marginal Risk (10-15% of neighborhood FFG exceedance). Due to convective trends and the 12z REFS/18z HREF guidance, there has some southward shift in the Marginal Risk area when compared to continuity. Isolated to widely scattered flash flood occurrences are possible. Roth Day 2 Valid 12Z Wed Mar 04 2026 - 12Z Thu Mar 05 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM NORTH TEXAS NORTHEASTWARD INTO THE OHIO VALLEY... 20z Update: Minimal changes made to the inherited risk. The threat across eastern OK, northwest AR and southern MO is right on the border of a higher end Marginal or lower end Slight risk, with localized rainfall over 3" likely. Given max hourly rain currently forecast to only peak ~1.5" and the dry antecedent conditions, we will continue to hold this at a Marginal, with primarily localized flash flooding expected. Chenard ...Previous Discussion... Minimal changes are made to the inherited outlook. At the mid- levels, an approaching trough will reach the central Plains during the forecast period. As this occurs, strengthening, confluent low- level flow from north Texas into the Missouri Ozarks will aid in moisture transport and eventually deep convective development especially during the afternoon/evening hours. That convective development will migrate from southwest to northeast within the aforementioned warm conveyor, with areas of training/repeating possible along with local rainfall totals exceeding 3 inches through 12Z Thursday. The collocation of these rainfall totals with varied/sensitive terrain over southwest Missouri/northwest Arkansas suggests that higher probabilities and a Slight Risk may need to be introduced at some point. Lingering concerns regarding antecedent conditions (very dry soils) and eventual convective evolution (models exhibiting a slight westward trend over the past 24 hours) gives pause on introducing an upgrade at this time, however. Current trends suggest that the greatest risk of flash flooding will exist along an axis from Fayetteville, AR to Rolla, MO, though this axis may change between now and Wednesday afternoon/evening. Farther northeast, areas of rain (approaching 1-1.5 inch total in spots) will develop from southern Illinois eastward through West Virginia in similar locations that are expected to receive 1-2 inches of rain during the D1 forecast period (Tuesday into Tuesday night). Soils should continue to moisten during this period, with isolated instances of flash flooding remaining possible. Cook Day 3 Valid 12Z Thu Mar 05 2026 - 12Z Fri Mar 06 2026 The probability of rainfall exceeding flash flood guidance is less than 5 percent. 20z Update: Additional convection is probable across portions of the OH valley. The current QPF is generally 1" or less, and this amount of rain would typically not produce a flood risk. However, heavier totals are possible, and hydrologic conditions will be more sensitive from the previous two days of rainfall. Thus we may eventually need to carry a Marginal risk here, but will hold off for now and continue to monitor both the forecast rainfall for this day, and how the previous rainfall impacts soil and streamflow conditions. Chenard ...Previous Discussion... Models are in general agreement that longwave trough will deepen across the Intermountain West, spreading southwesterly flow aloft over a large part of the Great Plains. Meanwhile, low-level moisture advection will aid in an airmass characterized by 1.25-1.5 inch PW values along and just east of a dryline generally extending from near Goodland to near Amarillo. Models depict scattered convection developing amid supercellular wind fields Thursday afternoon, with a mix of cells and linear segments possible along parts of the dryline. Local cell mergers may result in a couple spots of 2-3 inch rainfall totals in this regime, though the overall footprint of heavier rainfall should be too small to even delineate a Marginal Risk area at this timeframe. Antecedent dry conditions/drought are also mitigating factors for flash flood potential. This scenario will need to be monitored for any potential increase in convective coverage that might necessitate a Marginal in later outlooks. Cook 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