Weather context
Heat-adjusted race times
Hot, humid race days can slow finish times. The adjusted time estimates the equivalent effort in more neutral conditions. Official results, placement, pace, and standings never change.
Quick answer
A heat-adjusted time starts with your actual net time, then estimates how much race-day heat and humidity slowed the effort. The penalty comes from Wet Bulb Globe Temperature, or WBGT, race distance, and how long you were exposed to those conditions.
What WBGT means
WBGT is a heat-stress score built for people exercising outdoors. It is not the same as air temperature. Outdoor WBGT is 70% natural wet bulb, 20% globe temperature, and 10% air temperature, so humid air and direct sun can raise the number even when the thermometer reading looks manageable.
Natural wet bulb
A wet bulb temperature describes evaporative cooling. When the air is dry, sweat evaporates easily and this number stays lower. When humidity is high, sweat evaporates poorly and this number rises closer to the air temperature.
Globe temperature
Globe temperature represents radiant heat from the sun and surroundings, adjusted by wind. It is why a bright, still morning can feel harder than the air temperature alone suggests.
Air temperature
Air temperature, sometimes called dry bulb temperature, is the regular thermometer reading. It matters, but it is only one part of heat stress for runners.
What goes into the estimate
The estimate stays intentionally simple:heat penalty = heat above 59F WBGT x race-duration response x elapsed-time exposure
- Heat above 59F WBGT
- There is no heat penalty at or below 59F WBGT (15C). Above that point, each warmer step adds to the estimate.
- Race-duration response
- Distance changes how much heat matters. The model is anchored around 5K, 10K, and half-marathon efforts, with longer races receiving a larger response because exposure accumulates.
- Elapsed-time exposure
- Different runners in the same race can receive slightly different adjustments because a longer net time means more minutes running in the same heat.
The 5K and 10K anchors are intentionally close. A large event-specific WBGT study found a lower 10,000m signal among elite track performances, but recreational 10K treadmill research shows meaningful heat impairment. We use that elite signal as a guardrail, not the sole anchor. Half marathon sits higher because exposure accumulates over a longer effort. The final penalty is capped at 8%.
Example at 82F WBGT
A 30:00 5K at 82F WBGT (28C) receives about a 4.1% heat penalty, which estimates an equivalent effort of about 28:50. A 1:00:00 10K receives about a 4.2% penalty at the same WBGT, and a 2:00:00 half marathon receives about 5.2%.
5K
4.1%- Actual net
- 30:00
- Adjusted
- 28:50
10K
4.2%- Actual net
- 1:00:00
- Adjusted
- 57:34
Half marathon
5.2%- Actual net
- 2:00:00
- Adjusted
- 1:54:04
What this number can and cannot say
This is not a personal physiology model, a forecast, or a reranking. It does not know whether a runner was heat-acclimated, shaded by the course, carrying water, or having a rough day for unrelated reasons. It is context for comparing effort across very different race-day conditions, and it should be read as an estimate.
It uses a race-start weather snapshot, so it will not capture every shaded stretch, breeze, water stop, or late-race weather change. That keeps the number easy to understand, but it also means small differences should not be overread.