Dry and wet monthly precipitation tails had no clear persistence difference across 48 US states in 1951-2025

We compared dry-to-dry and wet-to-wet monthly precipitation probabilities across 48 contiguous US states in 1951-2025. We used NOAA nClimDiv v1.0.0, local calendar-month 20th and 80th percentiles, and 11 within-year month pairs. The equal-state probabilities were 23.362% and 23.382%. The difference was -0.020 percentage points, with a conditional 95% five-year block interval of -3.504 to +3.525 points. Independent calendar-month year shuffles within 15-year bands retained national spatial fields. Their exact expected probabilities were 20.590% and 20.426%. Both tails exceeded the reference, with two-sided Monte Carlo p=0.0005. Their contrast gave p=0.8240. Other thresholds and two 30-year periods gave no clear contrast. A zero-threshold exclusion removed no edge and adds no distinct evidence. The result shows short precipitation memory under the reference but no clear national tail asymmetry. It does not show equal persistence, a physical cause, water-store recovery or full spell duration. One product, fixed thresholds, equal state weights, omitted year-boundary pairs and reference assumptions limit the result. Code, aggregate evidence, source hashes, a retrieval script and an independent count audit are included.

precipitation · persistence · dry and wet tails · nClimDiv · null result · reference model