FOUS30 KWBC 231957 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 357 PM EDT Thu Apr 23 2026 Day 1 Valid 16Z Thu Apr 23 2026 - 12Z Fri Apr 24 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN THE CENTRAL PLAINS AND UPPER MIDWEST... 16Z update... Lines of thunderstorms are still expected to pass through the Mississippi Valley and Central/Southern Plains producing rainfall rates up to 2.5 inches/hour. Storm motion will be fairly progressive through this period so it may limit the overall risk to any particular location. Recent rains across the Upper Mississippi Valley/Upper Midwest has had time to absorb lower within the soil column allowing the top few inches to dry out. Parts of Wisconsin and surrounding areas may be more sensitive to flash flooding and stream rises should the storm speed slow or rates increase. At this time a Marginal still seems appropriate for the setup and risk level, only adjustment made was to extend the northern boundary to the International border of northeast Minnesota. Campbell Convection is expected to blossom this afternoon along and ahead of a cold front in the Central U.S. The warm sector ahead of the front should be characterized by an overlap of moderate instability (1000 to 2000 j/kg MLCAPE) and anomalously high moisture content (1.0 to 1.5 inch PWATs; near or above the 90th percentile for late April). The combination of instability and moisture should support heavy rain rates in organized convection in excess of 1 inch per hour at times. The main limiting factor for higher rainfall totals over the entire forecast period, and any impacts from flash flooding, should be a lack of persistence to the high rain rates in a given spot. From the I-70 corridor to the north, lines of thunderstorms are expected to be relatively narrow and steadily progress, given the deep layer shear vectors will be oriented closer to perpendicular with the cold front. Therefore, despite some pockets of lower flash flood guidance (around or just under 2 inches in 3 hours), and recent wet pattern in parts of the region, the heaviest rain rates should not last very long and the flash flood risk is expected to remain isolated. Furthermore, instability diminishes rapidly around sunset, so rain intensity should drop off within about 6 hours of convective initiation. It should be noted this assessment does not necessarily apply to other flooding risks in the region: ongoing mainstream river flooding, or potential for rain and snowmelt flooding in the Upper Peninsula of Michigan. For more details on those flooding hazards, refer to the National Water Center. Further south, the pattern will be more supportive of backbuilding and training convection, especially this evening and overnight from southeast Kansas into northeast Oklahoma and the Ozark region of southwest Missouri and northwest Arkansas. As the low level jet veers and an upstream instability maximum persists in eastern Oklahoma, hi-res models uniformly show a band of thunderstorms becoming increasingly east-west oriented, more parallel to the deep layer shear vector. Nevertheless, they all also show steady progression to the southeast with some cold pool development, and a lack of rainfall maxima in excess of 3 inches. Therefore, the risk of flash flooding is currently expected to be isolated, but the situation will be monitored in case a targeted Slight Risk is needed later today. Lamers Day 2 Valid 12Z Fri Apr 24 2026 - 12Z Sat Apr 25 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN THE MID SOUTH... 21Z update... A minor southeast nudge was made to the northwest side of the Marginal into Arkansas and a southeast nudge further into central Mississippi and western Alabama was made to reflect the latest trends and WPC QPF. There is an increasing signal for some of the heaviest rainfall to focus near/along the Arkansas and Mississippi border and surrounding counties. Consensus maintains rainfall rates of 1 to 2 inches/hour however the NAM Conest had a few hours where rates pulsed upwards of 4 inches/hour (possibly outflow enhanced) as cells approached far southeast Arkansas. Campbell A convective cluster or backbuilding convective line may be ongoing on Friday morning -- most likely across northern Arkansas based on 00Z HREF EAS probabilities -- with the potential for additional convective clusters to develop through the day across the region. Updated WPC QPF places the heaviest rainfall across Arkansas, northern Mississippi, and far northern Louisiana, and this is where the Marginal Risk area was re-centered. There is some uncertainty on where the heaviest rain will fall, as it should be tied in some way to convective outflow from morning and early afternoon activity. The warm sector to the south and southeast of that should have a combination of moderate instability and precipitable water close to 1.5 inches (around the 90th percentile for late April). That sort of environment would support rain rates of 1 to 2 inches per hour in organized convection, which could lead to isolated flash flooding where backbuilding and training occurs. Lamers Day 3 Valid 12Z Sat Apr 25 2026 - 12Z Sun Apr 26 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN SOUTHEAST KANSAS, SOUTHWEST MISSOURI, EASTERN OKLAHOMA, AND WESTERN ARKANSAS... 21Z update... A very minor northwest to southeast orientated expansion was made to the Marginal Risk. The latest guidance continues to vary where the heaviest rainfall will setup, however this is some overlap over eastern Oklahoma and western Arkansas. In general areal averages are in the 1 to 2 inch range with the potential for isolated maxes of 3 to 4 inches. Campbell Available deep moisture in the southern Plains on Saturday should be lower than prior days across the region, with model forecast soundings indicating the potential for dry air from 800-600mb associated with an elevated mixed layer. This would likely restrict any excessive rainfall and flash flooding concerns to the isolated variety. Nevertheless, strong instability and vertical wind shear should support supercells evolving into convective lines. There is not a consistent signal for concentrated areas of heavy rain, but with the expected convective modes, localized areas of longer heavy rain duration are possible via storm mergers and some upshear cell development. Any corridors of heavy rain on Thursday or Friday could also locally increase soil moisture and vulnerability to another round of heavy rain. Therefore, the Marginal Risk was maintained for Saturday and Saturday Night. Lamers 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