Winter ENSO links to monthly hourly high-to-low spans were uncertain at two Pacific gauges in 48 winters of 1961-2025

We tested whether concurrent winter ENSO was linked to the span between monthly hourly high and low water levels at San Francisco and Seattle. We used fixed NOAA data and 48 common complete winters within 1961-2025. Fits included a linear trend and fixed 18.61-year and 4.425-year cycle terms. The equal-site mean span slope was -1.56 cm per degree C of Nino 3.4. Its 95% five-year block interval was -3.88 to 0.92 cm per degree C. Without cycle terms, the slope was +1.54, with an interval of -2.60 to 5.19. All planned span checks left zero within the interval. The result does not establish that the span is constant or that ENSO has no effect. Paired high and low coverage excluded 17 winters, including 1998 and 2016. Two selected harbor sites, missing extremes, hourly sampling, unmeasured weather, and block assumptions limit inference. The package gives exact data extracts, shared source paths and hashes, code, saved draws, a figure, and a separate numerical audit.

ENSO · coastal water levels · monthly extreme span · hourly extrema · tidal cycles · null result · block bootstrap