Reference

Sources, Data & Attribution

Last updated: July 15, 2026

Everything quantitative on this site traces to three public datasets and one documented model. This page is the complete list, with the credit each source requires. External links below are attribution links (marked rel="nofollow"); they are the only external links on the site.

Climate normals — NOAA/NCEI

U.S. Climate Normals 1991–2020, National Centers for Environmental Information (NCEI), NOAA. We use the daily temperature normals (DLY-TMAX-NORMAL, DLY-TMIN-NORMAL) and the annual/seasonal first-freeze probability field (ANN-TMIN-PRBFST-T32FP50) for the station named in each city page's footer. NOAA data is produced by the U.S. government and is in the public domain. Dataset home: NCEI U.S. Climate Normals.

Live weather — Open-Meteo

Weather data by Open-Meteo.com, used for the live water-temperature estimate on city pages (past 21 days and 10-day forecast of daily highs and lows). Open-Meteo data is licensed CC BY 4.0; source: Open-Meteo. Requests go directly from your browser to Open-Meteo; this site's servers never see them.

City directory — SimpleMaps

City names, coordinates, populations, and time zones come from the SimpleMaps US Cities Database (Basic), used under its free license with this attribution.

Industry background

The qualitative guidance this site paraphrases — the ~70°F opening rule of thumb, the 65°F algae-acceleration zone, the close-cold-but-before-freeze principle, and the May/Memorial-Day demand peak — reflects the consistent published advice of major U.S. pool retailers, manufacturers, and industry education resources. We restate it in our own words, attach local numbers to it, and keep all chemical dosing at "follow the product label."

Typeface

Headings are set in Archivo (SIL Open Font License 1.1), self-hosted; body text uses your system's native font stack. No third-party CDNs, fonts, or trackers load on any page.

Citing this site

Model outputs (dates, windows, water estimates) are computed by PoolWindow as described on the methodology page and may be cited as "PoolWindow site model of NOAA 1991–2020 normals." Please don't present our modeled dates as NOAA's own publications — the normals are theirs; the interpretation is ours.