Green Velo - 05 Dolina Biebrzy i Narwi: which way and when to ride
The best month for Green Velo - 05 Dolina Biebrzy i Narwi is September: 80% of days were dry with highs of 10–30 °C. In September the wind barely favours either direction — on average 0.4 km/h along the route (ERA5 2006–2025, daytime 9:00–18:00).
Weather by month
| Month | Good days | Rain days ≥ 1 mm | Rain, mm | Avg high | Days ≥ 30 °C | Days < 10 °C | Daylight, h |
|---|---|---|---|---|---|---|---|
| January | 1% | 22% | 48 | 0 °C | 0% | 99% | 8.0 † |
| February | 1% | 18% | 38 | 1 °C | 0% | 98% | 9.7 † |
| March | 23% | 17% | 35 | 7 °C | 0% | 75% | 11.7 |
| April | 59% | 21% | 40 | 13 °C | 0% | 31% | 13.9 |
| May | 71% | 27% | 67 | 18 °C | 0% | 4% | 15.8 |
| June | 71% | 26% | 71 | 22 °C | 4% | 0% | 17.0 |
| July | 64% | 31% | 95 | 24 °C | 7% | 0% | 16.5 |
| August | 69% | 24% | 79 | 24 °C | 7% | 0% | 14.8 |
| September | 80% | 19% | 54 | 19 °C | 0% | 2% | 12.6 |
| October | 54% | 19% | 50 | 12 °C | 0% | 35% | 10.4 † |
| November | 12% | 18% | 41 | 6 °C | 0% | 85% | 8.5 † |
| December | 1% | 18% | 44 | 2 °C | 0% | 99% | 7.5 † |
Best months are all months within 3 percentage points of the best one. † less than 11 hours of daylight — long stages get tight.
Wind by month
| Month | Wind near Augustów → near Białystok, km/h | Headwind > 15 km/h, near Augustów → near Białystok | Headwind > 15 km/h, near Białystok → near Augustów | Better way |
|---|---|---|---|---|
| January | −1.6 | 12% | 8% | either |
| February | −1.1 | 10% | 9% | either |
| March | +0.3 | 9% | 10% | either |
| April | +1.2 | 6% | 11% | either |
| May | +1.1 | 6% | 8% | either |
| June | +1.4 | 4% | 8% | either |
| July | +1.3 | 4% | 7% | either |
| August | −0.4 | 5% | 5% | either |
| September | −0.4 | 7% | 7% | either |
| October | −1.8 | 10% | 7% | either |
| November | −3.0 | 11% | 6% | near Białystok → near Augustów |
| December | −2.3 | 12% | 7% | near Białystok → near Augustów |
Along the route (sections of about 25 km)
| km | Heading | Tailwind in September, km/h |
|---|---|---|
| 0–25 | S | −1.6 |
| 25–51 | SW | −2.2 |
| 51–76 | S | −1.3 |
| 76–102 | SE | +1.0 |
| 102–133 | E | +1.6 |
How to read the numbers
Wind is the 10 m wind of a 25-km grid cell, daytime hours 9:00–18:00 local solar time; at saddle height in a sheltered valley it is weaker, on a coast or ridge stronger. A positive value is a tailwind. ERA5 slightly over-counts days with ≥ 1 mm of rain (by about 5–7 percentage points) and underestimates daily highs by 1–2 °C. Good day = less than 1 mm of rain between 9:00 and 18:00 (riding hours, local solar time) and a high between 10 and 30 °C; rain at night or in the evening does not spoil it.