Subj : HVYRAIN: Excessive Rainfa To : All From : Mike Powell Date : Sun Dec 28 2025 09:05:01 FOUS30 KWBC 281008 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 508 AM EST Sun Dec 28 2025 Day 1 Valid 12Z Sun Dec 28 2025 - 12Z Mon Dec 29 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF WESTERN NEW YORK... ....New York... The warm front associated with a rapidly deepening low that will track from the central Plains to the northern mitten of Michigan today will move into western New York later this morning. This warm front will advect much warmer air behind it, to its south, which in turn will change over any wintry precipitation ahead of it to plain rain. Dynamics associated with the rapidly deepening low, including well above normal amounts of atmospheric moisture, some instability, and slow northward movement, will all allow rain, heavy at times, to persist from when it starts later this morning through into tonight, when the trailing cold front sweeps across western New York, ending any warm precipitation, as much colder Canadian air rushes in behind the cold front. This extended period of warm rainfall will occur over a below-normal, but still fairly robust snow pack at the higher elevations of the Southern Tier, to the amount of 1-4 inches of snow water equivalent. Thus, the combination of rain and snow melt should rapidly increase stream, creek, and river levels across western New York. Thus, the flooding threat has increased and a Slight Risk for portions of western New York, generally west of Rochester and north of the PA State Line, remains in place. Urban and small stream flooding look to be the types of flooding that are most likely, but any flood-prone area will be susceptible today and especially into tonight. ....Midwest... A Marginal Risk extends from northern Illinois across much of southern Michigan. The warm front with embedded elevated convection will persist through the entire day in the Marginal Risk area. The cold front will swing west to east from late this afternoon in Illinois to this evening across Michigan. This will effectively end the flooding threat as much colder air turns any lingering precipitation tonight over to snow, and the lakes help with localized enhancement across western lower Michigan. Urban and small stream flooding are possible in the Chicago area, Detroit, and any smaller urbanized areas in between. Due to relatively dry conditions across the Midwest prior to today, any instances of flooding should be isolated. The rain has already started out this early morning to the southwest of the Marginal Risk area across portions of Missouri, Iowa, and western Illinois. For these areas, even drier soils prior to this storm should keep the flooding threat below the 5% Marginal Risk threshold, but the area will be monitored for overperformance and any potential need to extend the Marginal Risk south and west for the morning into these areas. Wegman Day 2 Valid 12Z Mon Dec 29 2025 - 12Z Tue Dec 30 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman Day 3 Valid 12Z Tue Dec 30 2025 - 12Z Wed Dec 31 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman $$ --- SBBSecho 3.28-Linux * Origin: Capitol City Online (618:250/1) .