Forsythia Forsythia × intermedia
Expected first-bloom dates for spring 2027 in 16 cities.
| City | Status | Expected start | Likely range | Label | Model MAE (d) | Climatology MAE (d) | Obs. years |
|---|---|---|---|---|---|---|---|
| Berlin | Season over | ~24 Mar 2027 | 10 Mar – 10 Apr | validated | 4.1 | 9.83 | 34 |
| Hamburg | Season over | ~23 Mar 2027 | 9 Mar – 12 Apr | validated | 4.36 | 10.93 | 35 |
| Munich | Season over | ~28 Mar 2027 | 15 Mar – 11 Apr | validated | 4 | 9.13 | 35 |
| Cologne | Season over | ~15 Mar 2027 | 5 Mar – 3 Apr | validated | 3.97 | 9.74 | 35 |
| Frankfurt | Season over | ~17 Mar 2027 | 5 Mar – 3 Apr | approximate | 5.39 | 8.71 | 35 |
| Stuttgart | Season over | ~17 Mar 2027 | 6 Mar – 3 Apr | validated | 4.53 | 8.58 | 35 |
| Dresden | Season over | ~24 Mar 2027 | 10 Mar – 10 Apr | validated | 4.38 | 9.39 | 34 |
| Hanover | Season over | ~19 Mar 2027 | 7 Mar – 8 Apr | validated | 4.71 | 11.23 | 35 |
| Leipzig | Season over | ~22 Mar 2027 | 8 Mar – 8 Apr | approximate | 5.09 | 9.97 | 34 |
| Nuremberg | Season over | ~26 Mar 2027 | 12 Mar – 8 Apr | validated | 3.99 | 8.47 | 35 |
| Stockholm | Season over | ~20 Apr 2027 | 9 Apr – 4 May | approximate | n/a | n/a | 0 |
| Uppsala | Season over | ~24 Apr 2027 | 12 Apr – 4 May | approximate | n/a | n/a | 0 |
| Gothenburg | Season over | ~4 Apr 2027 | 25 Mar – 23 Apr | approximate | n/a | n/a | 0 |
| Malmö | Season over | ~29 Mar 2027 | 16 Mar – 20 Apr | approximate | n/a | n/a | 0 |
| Linköping | Season over | ~14 Apr 2027 | 6 Apr – 30 Apr | approximate | n/a | n/a | 0 |
| Örebro | Season over | ~17 Apr 2027 | 8 Apr – 1 May | approximate | n/a | n/a | 0 |
Backtest (leave-one-year-out)
| Country | City-years | Model MAE | Simple climatology MAE | Within ±5 days |
|---|---|---|---|---|
| Germany | 347 | 4.45 d | 9.6 d | 69% |
| Sweden | not enough open observations for a local backtest | |||
Model parameters
- Germany: sum of daily mean temperature above 0 °C from 1 Feb; bloom when the sum reaches 189 °C·days (fitted on 347 city-years)
- Sweden: sum of daily mean temperature above 0 °C from 1 Feb; bloom when the sum reaches 189 °C·days (parameters transferred from Germany — unchecked)
MAE = mean absolute error in days. “Climatology” = just using the average date of the other years. Details and limits: How it works.