FOUS30 KWBC 170037 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 837 PM EDT Sat May 16 2026 Day 1 Valid 01Z Sun May 17 2026 - 12Z Sun May 17 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE CENTRAL PLAINS AND MID-MISSISSIPPI VALLEY... ...Central Plains to Mid-Mississippi Valley... Conditions remain ripe for a period of heavy rainfall this evening encompassing portions of the Central Plains to the Mid-Mississippi Valley as large scale ascent coupled with focused surface fronts/boundaries allow for a targeted area of interest through the evening period. LLJ is forecast to develop further over the course of the early evening leading to enhanced convergence regime in the vicinity of a quasi-stationary front analyzed over IA, across into eastern NE and northern KS. Shortwave trough ejecting out of the Central Rockies will provide a focused area of upper forcing as moderate positive vorticity advection, along with a broad axis of upper diffluent flow will inspire a blossoming convective field that is currently in the works based on the latest radar. 18z HREF remained bullish for a west to east alignment of heavy precip located between northeast KS, southeast NE, southern IA, and northern MO, much of the area focused within the stationary front, and a remnant surface boundary stemming from previous convection. Deep moist environment remains in place with PWATs between 1.5-1.8", good enough for +2 standard deviations according to NAEFS forecasts and verified 75-90th percentile climatological PWATs from forecast sounding analysis in the area. Sufficient low- level buoyancy and shear will maintain stronger cell cores for several hours before finally waning as we approach the back half of the rest of D1. Considering the anticipated environmental favorability and maturation of the ongoing convective setup (For more information, see Mesoscale Precipitation Discussions #174 and #175), the SLGT risk from previous remains in place with a MRGL encompassing. ...Mid-Ohio Valley... Lingering heavy rainfall stemming from a modestly favorable environmental regime and lower FFG's compared to the rest of the Ohio Valley allowed for a continuation of the previous MRGL risk focused over portions of the Ohio River Basin. This threat will continue for another few hours before dwindling with the greatest threat likely closer to Louisville to Cincinnati where urbanization factors skew towards a slightly more favorable risk for flash flooding. The threat remains on the lower end of the risk threshold, but an isolated warning could not be ruled out given the latest radar indications. Kleebauer Day 2 Valid 12Z Sun May 17 2026 - 12Z Mon May 18 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE CENTRAL PLAINS THROUGH THE UPPER MIDWEST AND IN SOUTHEAST LOUISIANA... ...Central Plains through Upper Midwest... Broad low level flow feeding plentiful moisture and sufficient instability ahead of a strengthening inverted trough from a lee- side low over the southern High Plains will allow thunderstorms from the central Plains through the Upper Midwest. Focus for this activity is less certain, but should be close to the inverted trough axis from central KS to western Lake Superior and from boundaries left from activity tonight. Consensus is for late afternoon activity to proceed through the overnight which coincides with strengthening right entrance jet dynamics and the nocturnal low level jet. The Marginal Risk was expanded a bit in northeastern KS and eastern SD per the 12Z CAM consensus. Should greater focus or overlap of heavy rain areas from tonight become more clear, a targeted Slight Risk could be warranted given PW anomalies approaching 2 sigma over normal. ...Southeast Louisiana... Trough amplification over the west, with an axis shifting down the Rockies through Sunday night, along with a persistent Bermuda High will promote broad and prolific moisture advection from the western Gulf. A notable gradient in moisture is evident in consensus guidance Sunday over the lower Miss Valley. This gradient should provide sufficient focus/forcing for thunderstorm development with a risk for repeating activity over southeast Louisiana. The 12Z ARWs, HRRR, and RRFS agree on a 2-3" QPF max west of I-55 and northwest from NOLA. A Marginal Risk is introduced in collaboration with WFO LIX. Jackson Day 3 Valid 12Z Mon May 18 2026 - 12Z Tue May 19 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE CENTRAL PLAINS INTO THE UPPER MIDWEST... The base of the trough digging down the Rockies pivots east across Colorado Monday before lifting northeast to the Upper Midwest Monday night. There will be ample moisture from days of Gulf moisture advecting up the Plains and the forcing will be stronger than Sunday both with the upper jet and in the low levels as the surface low ejects east along the inverted trough that sets up Sunday. The focus for heaviest rain should still be a bit south and east of the the activity on Sunday, but there could be notable overlap of heavy rain from tonight over northeast KS, northwest MO into IA and southeast Neb. The 12Z GFS/CMC/UKMET/RRFS/EC-AIFS all agree on QPF maxima through this area with totals potentially exceeding 5". The 12Z operational EC is still more distinct, but did trend a bit toward the consensus. While the Slight Risk for this area remains in place, this area is now considered to be a higher end Slight Risk. There is less certainty on the north end of the axis of heavy rain in eastern MN into WI, but enough from the 12Z CMCreg and EC/EC- AIFS to warrant maintenance of the Slight Risk with some expansion east through the Mississippi River. The eastward extend of activity Monday night looks also to be more expansive, so the Marginal Risk was brought into northern IN and through the St. Louis metro area. Given the abundant moisture advection (PW anomalies of 2 to 2.5 sigma above normal from the western Gulf Coast to the western Great Lakes by Monday afternoon), the southern extent of the heavier precip will need to be monitored and further southern expansions could be warranted. Jackson 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