One report per hour (the routine report nearest the top of the hour). Months follow the UTC date; hours are local standard time (no daylight time) or UTC.

Filters combine. Every chart ignores its own filter so you can click it: the rose ignores direction, the month × hour grid ignores months and hours, the year chart ignores years. Percentages with fewer than 30 hours behind them show “—”.

Flight categories: LIFR ceiling below 500 ft or visibility below 1 SM; IFR below 1000 ft or 3 SM; MVFR 1000–3000 ft or 3–5 SM. Below alternate / below landing use each airport's validated MANAIR Appendix A limits (not shown where none are validated).

All sources adds NOAA ISD hourly reports from before our METAR archive; older reports were coded differently, so compare eras with care. Not an official climate product.