Is 80 degrees too hot to race in?

80? That's cute.

I just ran an evening 5K and the heat index was 94°F, temp 85°F. I felt the same way as you. But I ran it knowing it wasn’t PR conditions.

I didn’t set a PR but learned what I’m capable of in those conditions. Plus everyone else was slow, so it was a level playing field as far as placement. It was good heat training. Now when I run another 5K in the morning in two weeks, 78°F will feel like heaven

Humidity is usually much higher in the morning. 78 with high humidity may not feel that much easier than 85 with lower humidity. Still, the heat training should help.

I’ve ran when the dewpoint is 80. You guys are too soft.

With temperature the answer is always "It depends" It depends on the time of day. If the Sun is low on the horizon and you're running in the shade you should be OK. It depends on the dew point.

Example:

5.14.2010 DOHA

Kipchoge 12:51

Chepkok 12:51

================================

There is temperature and there is temperature. Temperature is a measurement. Humidity is a measurement.

The key measurement of energy in the air is DEW POINT.

The race was run at night. Sunset at near the Equator is 6:00pm. That means the race went off two and a half hours past sunset. There is NO radiant energy coming from the Sun at ground level. There is little stored energy (comparatively) in the air. It's a good time to run.

The 5000m went of at 8:35pm. The temperature was about 94, the DEW POINT was 54. In other words it was ideal for running fast. The physiological benefits of a higher entropy without barriers to heat dissipation.

The Dew Point Temperature - A Better Approach
Steven L. Horstmeyer

The Concept
Humidity is a complicated concept. Humidity refers toevaporated water substance in the air, i.e. water vapor. For years relativehumidity has been what we use to inform the TV audience, but it has many pitfalls and to tell you the truth almost no one understands it, including many meteorologists.

Think Energy
When thinking of humidity you always have to think interms of energy. Of course this is expressed as temperature. There is only somuch energy to go around and only a certain part of the thermal energy can go to do the work of evaporation. The rest goes to the other molecules in the air.

Relative humidity expresses how much of the available energy has been used. A relative humidity of 50% means half the energy has been used to evaporate water from the ground, streams, lakes anywhere else it is and 50% is still available to do more evaporation.

Relative to What?

On a summer morning the temperature may be 75 degrees and the relative humidity 90%, a very sticky morning indeed. Without changing the amount of water vapor in the air if the temperature hits 92 degrees in the afternoon the relative humidity is 52%. Relative humidity is RELATIVE TO THE AMOUNT OF ENERGY AVAILABLE Because the amount of energy increased as the sun warmed the atmosphere the percentage of the energy used decreased, i.e. the relative humidity, all the while there was no change in the amount of vapor in the air.

So when you hear someone say its feels worse than 52% relative humidity today, they do not understand the concept of RELATIVE HUMIDITY. Ninety-two degrees and 52% is a very humid afternoon. Because the concept is confusing many meteorologists are trying to get use dew point temperature.

The Dew Point Temperature
Dew point temperature is a measure of humidity. If you take a parcel of air, and cool it, eventually you will remove enough energy to begin to get water vapor to condense. Remember the water vapor was originally liquid water and to get it to evaporate you had to add energy. As long as it hassufficient energy it will remain vapor, but as you cool it at some point condensation will occur. The temperature where condensation begins is the dew point temperature. In terms of relative humidity, as the parcel of air is cooled, the relative humidity increases, when the relative humidity reaches 100%, you are at the dew point temperature.

Dew Point vs. R.H.
Unlike relative humidity if dew point increases, it is only because the amount of moisture increases. If relative changes it can be because of temperature change or moisture change, two variables leads to too many possibilities, with dew point it is strictly moisture you are tracking. Dew point can never be higher than the temperature, at saturation, i.e. 100% relative humidity the temperature and dew point are the same. …

So How Does Dew Point Feel?
On a typical summer day the following apply:
________________________________________
• Dew
Point(F)..........Perception
________________________________________
• 75+....................Extremely uncomfortable
• 70-74...................Very humid, quite uncomfortable
• 65-69...................A bit uncomfortable for most people
• 60-64...................Ok for most, but everyone begins to feel the humidity
• 55-59...................Comfortable
• 50-54...................Very comfortable
• less than 49...................Feels like the west, very pleasant, a bit dry to some

A Common Misconception
One last thing if you ever hear someone say it was 90 degrees and the humidity was 90%, that has never happened in Cincinnati, (and unless the greenhouse effect goes into overdrive never will). 90 deg/90% requires a dew point of 85.5 degrees. In Cincinnati the highest ever dew point was 81 deg. for just a few minutes.

In August 1995 we had four hours of 78,79,78,77 degree dew points, the highest persistent dew points I have seen in Cincinnati since working here as a meteorologist. For one hour I did see a dew point of 81, just after a thunderstorm.

World Record Dew Points

However veterans of the Persian Gulf War know what 90/90 feels like. The Persian Gulf and Red Sea both attain sea water temperatures in the mid 90's. That's plenty of energy, along with the 115 degree air temperatures, to evaporate water. The dew point has been measured on the shore of Ethiopia, the area is now part of Eritrea, at 94 deg. F. The highest known dew pointtemperature in the world. The relative humidity with a temp of 115 and a dewpoint of 94 is 54% this doesn't tell you as much as the dew point when you
consider the table above.

Amen, to low dew points being super helpful for racing fast.

Tell you what.

You run it, then tell us how it went.

Interesting explainer, there. Thanks, malmo .

My advice is to just stop running. For good. Once it goes over 80, all bets are off and it’s only uphill all the way until you roll off the top.

Well, first of all I want to run a PB and if I can't do that then there's no point in turning up and I'll do parkrun instead. So I wanted some advice. You see I've never done an evening run in the heat. I haven't been running very long.

I live in the UK and our heat is different... I'll find the weather stats.

80 is the same heat anywhere (with the same humidity).

Temp 84 degrees

Wind 5 mph

Humidity 31%

Dew pt 55

That's comfortable the chart says, somebody provided here.
It's not even 29 Celcius. I would call that warm but not hot.

But I don't live in the UK where they are not used to these kind of temperatures.

Anyway, enjoy your 5k, you will survive, I am sure.

So How Does Dew Point Feel?
On a typical summer day the following apply:
________________________________________
• Dew
Point(F)..........Perception
________________________________________
• 75+....................Extremely uncomfortable
• 70-74...................Very humid, quite uncomfortable
• 65-69...................A bit uncomfortable for most people
• 60-64...................Ok for most, but everyone begins to feel the humidity
• 55-59...................Comfortable
• 50-54...................Very comfortable
• less than 49...................Feels like the west, very pleasant, a bit dry to some

This would be considered comfortable weather in most of the world.

If you're relatively new to running you should use this as training because the PBs are going to keep coming off and on for several years.

It's certainly possible for someone to set a 5K PB in those conditions if they're in PB shape. Last year I set an age-graded pb (I'm old) and was only a few seconds off an overall PB when it was 82 degrees with a 64 dew point, so a bit worse than what you'll have. It probably will help that (I assume) you're somewhat acclimated to warm temperatures this late in a hot summer.

80 degrees and 80% humidity was a typical 6:30am morning run for me a good 6-8 months out of the year.

I've run much longer races with much higher temperatures. At something as short as 5 km I would not rule out a PB, though I wouldn't bet on one either.