Eleven paired cold Pacific episodes gave no clear second-winter rainfall decline in Arizona and New Mexico in 1951-2025

We tested whether the second winter of a cold Pacific episode was drier than the first in Arizona and New Mexico. We used NOAA nClimDiv precipitation and ERSSTv5 sea temperatures for 1951-2025. Cold means an October-February Nino 3.4 anomaly at or below -0.5 C against the fixed 1991-2020 reference. We used the first two winters of each run and gave equal weight to states and to divisions within states. Across 11 pairs, November-March precipitation rose by 7.57 percentage points of reference precipitation. The episode bootstrap 95% interval was -24.72 to 38.18 points. A paired sign-flip test gave p = 0.684. Six pairs were drier in the second winter. Threshold, season and rainfall-reference checks left the change uncertain. A post hoc DJF ONI definition gave eight pairs and an uncertain rise of 16.35 points. The result does not show that repeated La Nina winters have no effect. Fixed-reference event selection, few episodes, revised data and equal spatial weights limit inference. Precipitation alone does not measure water supply or drought recovery. The package gives source snapshots, hashes, paired evidence, code, a figure and an arithmetic audit.

La Nina · precipitation · Southwest · paired episodes · null result · nClimDiv · ERSSTv5