Saint-Jacques à Vélo par la vallée d'Eure 2/4: which way and when to ride
The best month for Saint-Jacques à Vélo par la vallée d'Eure 2/4 is September: 79% of days were dry with highs of 10–30 °C. In September the wind barely favours either direction — on average 0.3 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 | 19% | 21% | 60 | 7 °C | 0% | 72% | 8.8 † |
| February | 34% | 22% | 52 | 9 °C | 0% | 55% | 10.2 † |
| March | 55% | 26% | 59 | 12 °C | 0% | 28% | 11.8 |
| April | 74% | 23% | 48 | 16 °C | 0% | 5% | 13.6 |
| May | 71% | 28% | 71 | 19 °C | 1% | 1% | 15.1 |
| June | 71% | 22% | 59 | 23 °C | 7% | 0% | 16.0 |
| July | 70% | 16% | 44 | 26 °C | 15% | 0% | 15.6 |
| August | 71% | 15% | 44 | 25 °C | 15% | 0% | 14.3 |
| September | 79% | 16% | 47 | 22 °C | 4% | 0% | 12.5 |
| October | 76% | 22% | 75 | 17 °C | 0% | 2% | 10.7 † |
| November | 50% | 24% | 64 | 11 °C | 0% | 32% | 9.2 † |
| December | 24% | 22% | 67 | 8 °C | 0% | 63% | 8.4 † |
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 Montreuil → Châtellerault, km/h | Headwind > 15 km/h, Montreuil → Châtellerault | Headwind > 15 km/h, Châtellerault → Montreuil | Better way |
|---|---|---|---|---|
| January | −4.0 | 21% | 6% | Châtellerault → Montreuil |
| February | −2.9 | 20% | 9% | Châtellerault → Montreuil |
| March | −1.0 | 16% | 11% | either |
| April | +0.8 | 10% | 11% | either |
| May | +0.5 | 11% | 10% | either |
| June | −0.1 | 9% | 7% | either |
| July | −1.8 | 12% | 5% | either |
| August | −1.8 | 10% | 4% | either |
| September | −0.3 | 10% | 7% | either |
| October | −2.7 | 16% | 6% | Châtellerault → Montreuil |
| November | −4.4 | 21% | 5% | Châtellerault → Montreuil |
| December | −5.0 | 23% | 6% | Châtellerault → Montreuil |
Along the route (sections of about 25 km)
| km | Heading | Tailwind in September, km/h |
|---|---|---|
| 0–25 | SE | +1.6 |
| 25–51 | S | −0.7 |
| 51–76 | SW | −2.0 |
| 76–101 | S | +0.9 |
| 101–126 | SW | −0.9 |
| 126–151 | S | −0.1 |
| 151–177 | SW | −1.4 |
| 177–202 | SW | −1.5 |
| 202–228 | S | +0.3 |
| 228–253 | S | −0.2 |
| 253–279 | SW | −0.7 |
| 279–304 | S | −0.1 |
| 304–329 | S | 0.0 |
| 329–351 | S | +0.4 |
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.