FOUS30 KWBC 161937 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 337 PM EDT Sat May 16 2026 Day 1 Valid 16Z Sat May 16 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... Upgrade to Slight Risk for northern MO into IA back along KS/Neb border into western IL with note on this being a dynamic situation that may require adjustments heading into tonight. Warm and moist advection ahead of a low over western KS will continue to converge along a stationary front and additional surface troughs through tonight. Convection on outflow from earlier activity continues to grow over northern MO into western IL with 1500 J/kg MLCAPE and 1.5" PW. 12Z HREF and recent HRRRs have struggled with this morning activity, though the 12Z RRFS is decent. This ongoing activity should wane through midday, but help define the boundary for redevelopment along and farther west into KS/Neb this afternoon/evening. PW should be 1.75" by then which is 2 sigma above normal and instability will be ample, 2000-3000 J/kg of MLCAPE promoting heavy thunderstorm development. Little synoptically forced movement is expected for this activity as the surface low remains in the southern High Plains/retrogrades west as the next shortwave trough approaches from the northern Rockies. Despite parched conditions, the risk for 3-5" is great enough (12Z HREF has 60% probability for 5" 18Z to 06Z along the IA/MO border) that a Slight Risk upgrade was coordinated with OAX/EAX/DMX/DVN. Thunderstorm development near the western KS/Neb border should increase through this evening. Backbuilding could cause a localized flash flood threat, so the Marginal Risk was expanded farther west. ...Lower to Mid Ohio Valley... Low level convergence of southerly flow continues over southern IL through the OH/KY border today with PW up to 1.5" (1.5 sigma above normal) and MLCAPE increasing to around 1500 J/kg. General thunderstorms with some repeating risk allows maintenance of the Marginal that was connected to the central Plains per morning radar trends. Jackson 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