The most recent edition on this page is dated Sep 6, 2026. The next edition date is not locked here yet. Use the historical race-morning weather on this page for planning until the next date is published.
Half
The Big Half
2027 date not locked yetTower Bridge to Cutty Sark, London, UK
Goal time
1:35:00
Adjusted time (preview)
About 36 m of climbing and 40 m of descent. Mostly flat.
Almost all within 2%No grades over 6%One small rise
Impacts
Based on the historical mean for the race window over the last 10 years, ±5 days.
Elevation
Heat
Wind
Total Impact
Race Pass: personalised finish time, adjusted splits, and your race-day pacing plan.
Historical weather
1 held edition. Race mornings only, not nearby dates. This is not a forecast.
18°C
14 - 21°C range
Overcast on average
Historical: overcast, with moderate winds
Historical average
1 held edition. Race mornings only, not nearby dates.
2026
Cloud Cover
76%
12 - 100% range
Wind
11km/h
2 - 24 km/h range • prevailing W
Humidity
79%
66 - 92% range
WBGT
15.8°C
14.5 - 15.9°C range
Race morning history
Last 10 years, around the 09:00 start hour. Typical early-September air averages 18°C (about 13°C to 22°C in that window). The bands are that history, not a forecast range. Hover or drag to explore.
Race-morning temperature
Most mornings
15-20°C
Almost all
14-21°C
Humidity
79%
Dew
14°C
WBGT
16°C
18°CAverage
09:00-10:35
Almost all (90%)Most mornings (70%)AverageRain
Year pills: green is favorable heat. Amber is moderate. Red is challenging.
Blue is most mornings. Dashed lines are the rare tails. Pink is the average. The bands are historical race mornings, not a forecast range. Blue columns are rain on the right scale. This assumes a 1:35. You can set your own time in the app.
Typical race-morning wind
Where the wind usually came from on race morning, not where it was going.
SW
Most frequent (15%)
Wind speed
0-6 km/h
6-13 km/h
13-21 km/h
21+ km/h
Year pills: green is favorable wind. Amber is moderate. Red is challenging. Colours assume no drafting.
A start that feels cool is not a promise about the second half.
Related races
Same city, region or country, when we can resolve them. World majors also point to each other.
- London Landmarks Half Marathon
- London Marathon
- Saucony London 10K
- Vitality London 10,000
- Hackney Half Marathon
- Oysho Royal Parks Half Marathon
View race map for this area.
Make sense of the conditions
- Dew point, WBGT and running in the heat
Read the heat and humidity before deciding what pace makes sense.
- When drafting helps your running pace
A group can help, but its pace and the conditions still need to suit you.
- Pacing the climbs and descents
Use the course profile to think about effort, not just splits.
Pacing and conditions FAQ
Beyond conditions
Conditions are only part of the race-day loss
Pacing mistakes often add several minutes, sometimes more than conditions alone, especially when the course and conditions are not ideal.
What your plan includes
Everything you need to turn this race preview into a usable race-day plan.
Personalized pacing
Effort and pace guidance tuned to this course profile.
Weather-adjusted splits
Split targets that account for heat, wind, and elevation.
Heat adaptation & drafting
Adjust for your heat tolerance and drafting preferences.
Get your personalised race plan for The Big Half.
Pacing, splits, and race-day strategy personalised to your fitness and this course.
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