Cherry bloom timing tracks accumulated warmth. We sum daily growing-degree-days (GDD = max(0, mean temp − 5°C)) from Feb 1 and project the crossing of calibrated thresholds:
| Milestone | GDD | |
|---|---|---|
| Bloom (開花) | 137 GDD | benchmark tree opens |
| Full bloom (満開) | 212 GDD | peak viewing |
After full bloom, rain is the physical trigger that drops petals. Our rain rules called every 2026 event correctly:
| Forecast seen on | Our call | Actual | Verdict |
|---|---|---|---|
| 3/31 | 15mm rain forecast for 4/1 | season ended 4/6 | ✅ 5-day early warning |
| 4/1 | continuous rain — last chance today | season ended 4/6 | ✅ correct |
| 4/3 | petals may scatter (4/4 rain) | heavy falling 4/5 | ✅ correct |
Once one region blooms we project the others from measured delays — the wave runs south/west → north/east:
| From | To | Delay | Confidence |
|---|---|---|---|
| Tokyo | Kansai | +1–3 days | high |
| Tokyo | Tohoku (Sendai) | +14–18 days | medium |
| Tokyo | Hokkaido (Sapporo) | +25–30 days | medium |
| Kyushu (Fukuoka) | Tokyo | −3–5 days (Kyushu first) | high |
Dated 2027 predictions (first bloom and full bloom per region) are published on this page in January–February 2027, once winter GDD accumulation begins. Until then, the model above and the measured delays are the best guide to relative timing: Kyushu first, Tokyo and Kansai in late March, Tohoku in mid-April, Hokkaido from late April onward.
Dated per-region 2027 predictions are published on this page in January–February 2027, once winter GDD accumulation begins. The bloom wave typically runs Kyushu → Tokyo/Kansai (late March) → Tohoku (mid-April) → Hokkaido (late April onward).
A growing-degree-day (GDD) heat-sum model from Feb 1, calibrated to 137 GDD for first bloom and 212 GDD for full bloom in Tokyo, plus rain-impact rules for the end of the season and a measured cross-region delay table.
All three 2026 rain-impact calls were correct, including a 5-day-early warning that the season would end on 4/6.
Kyushu blooms ~3–5 days before Tokyo; Kansai +1–3 days after Tokyo; Tohoku +14–18 days; Hokkaido +25–30 days.
Methodology & 2026 accuracy from first-party data · JapanSakura · japansakura.live