The best time to visit Luxembourg is May–Sep. It is the only stretch of the year — 5 months — rated go on both daytime heat and rainfall.
Mild; summer warm & busy
| Month | High °C | High °F | Rainy days | Verdict |
|---|---|---|---|---|
| January | 3.3 | 38 | 43% | Too cold |
| February | 4.8 | 41 | 40% | Too cold |
| March | 9.3 | 49 | 37% | Fair |
| April | 13.8 | 57 | 35% | Fair |
| May | 17.8 | 64 | 41% | Go |
| June | 21.6 | 71 | 42% | Go |
| July | 24.6 | 76 | 42% | Go |
| August | 24.7 | 76 | 38% | Go |
| September | 20.3 | 69 | 34% | Go |
| October | 14.4 | 58 | 39% | Fair |
| November | 7.8 | 46 | 44% | Fair |
| December | 3.9 | 39 | 49% | Too cold |
Verdict combines mean daytime high with rainy-day frequency. “Rainy days” is the share of days in the month with at least 1 mm of rain.
September is the driest month, with rain on 34% of days and daytime highs near 20.3°C (69°F). December is the wettest, at 49%. Temperature swings hard across the year — 21.4°C between August (24.7°C / 76°F) and January (3.3°C / 38°F) — so packing for the wrong month is the main risk. The record rules out too cold in Dec–Feb.