The upper daily water-level range gap rose at Seattle in cycle-adjusted fits to retained 1960-2024 records

We tested whether large daily water-level ranges moved farther from typical ranges at six US gauges. Each annual value is the mean of twelve monthly differences between the 95th percentile and median daily hourly range. We used fixed NOAA records and retained 333 station-years in 1960-2024. A trend fit with an 18.61-year cycle gave a Seattle rise of 6.11 mm per decade. Its marginal 95% interval was 2.81 to 9.41 mm per decade. The Holm-adjusted p value across six gauges was 0.0029. A five-year wild block family interval was 0.40 to 12.22 mm per decade. The other five primary tests did not resolve a trend. Seattle retained a positive point estimate but lost family significance without cycle terms and with a 1980 start. This is a change in a distribution measure under a tested model. It does not identify a tide constituent, storm trend, flood return level, or physical cause. Selected harbor gauges, missing years, source changes, and the short record limit inference. Code, daily evidence, source hashes, figures, and repeat instructions are included.

daily water-level range · upper quantile gap · NOAA CO-OPS · nodal cycle · trend uncertainty