National Cycle Network Route 4, stage 4: Pontypridd → Carmarthen
On stage 4 (Pontypridd → Carmarthen, 126 km) the best month is September: 70% of days were dry with highs of 10–30 °C, and riding Carmarthen → Pontypridd meant an average tailwind of 3.5 km/h (ERA5 2006–2025, 9:00–18:00).
← National Cycle Network Route 4 (Whole route)
Weather by month
| Month | Good days | Rain days ≥ 1 mm | Rain, mm | Avg high | Days ≥ 30 °C | Days < 10 °C | Daylight, h |
|---|---|---|---|---|---|---|---|
| January | 8% | 33% | 121 | 8 °C | 0% | 80% | 8.3 † |
| February | 10% | 30% | 95 | 8 °C | 0% | 82% | 9.9 † |
| March | 29% | 30% | 87 | 9 °C | 0% | 60% | 11.7 |
| April | 61% | 26% | 61 | 12 °C | 0% | 21% | 13.8 |
| May | 67% | 32% | 85 | 15 °C | 0% | 2% | 15.6 |
| June | 69% | 31% | 87 | 17 °C | 0% | 0% | 16.6 |
| July | 66% | 34% | 100 | 19 °C | 0% | 0% | 16.2 |
| August | 65% | 35% | 105 | 18 °C | 0% | 0% | 14.6 |
| September | 70% | 30% | 100 | 17 °C | 0% | 0% | 12.6 |
| October | 64% | 34% | 130 | 14 °C | 0% | 3% | 10.5 † |
| November | 37% | 37% | 135 | 11 °C | 0% | 33% | 8.7 † |
| December | 16% | 36% | 149 | 9 °C | 0% | 61% | 7.8 † |
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 Pontypridd → Carmarthen, km/h | Headwind > 15 km/h, Pontypridd → Carmarthen | Headwind > 15 km/h, Carmarthen → Pontypridd | Better way |
|---|---|---|---|---|
| January | −4.0 | 27% | 13% | Carmarthen → Pontypridd |
| February | −2.7 | 26% | 16% | Carmarthen → Pontypridd |
| March | −1.4 | 21% | 17% | either |
| April | −0.3 | 17% | 16% | either |
| May | −2.9 | 22% | 11% | Carmarthen → Pontypridd |
| June | −3.7 | 20% | 8% | Carmarthen → Pontypridd |
| July | −6.3 | 26% | 6% | Carmarthen → Pontypridd |
| August | −6.2 | 29% | 8% | Carmarthen → Pontypridd |
| September | −3.5 | 23% | 12% | Carmarthen → Pontypridd |
| October | −1.6 | 21% | 16% | either |
| November | −3.5 | 25% | 14% | Carmarthen → Pontypridd |
| December | −4.0 | 27% | 14% | Carmarthen → Pontypridd |
Along the route (sections of about 25 km)
| km | Heading | Tailwind in September, km/h |
|---|---|---|
| 372–397 | W | −6.7 |
| 397–422 | NW | −4.6 |
| 422–447 | W | −4.4 |
| 447–473 | NW | −4.3 |
| 473–499 | N | +2.4 |
Other stages
- London → Reading 116 km
- Reading → Bath 128 km
- Bath → Pontypridd 129 km
- Pontypridd → Carmarthen 126 km
- Carmarthen → Fishguard 147 km
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.