How hot is too hot (weather)?

I’m going to an eventing derby this weekend where the weather is scheduled to be 99 degrees both days, rising over 100 int he days that follow.

What’s your limit? Any articles that discuss the upper limit of temps to even risk?

This is low level stuff, to be sure, but mare will do 2 dressage test one day and 2 jump rounds the next.

The critical factor here will be how humid will it be? If it’s humid, sweat won’t evaporate, and your horse won’t be able to cool themselves appropriately.

I think this chart is probably a good rule of thumb. 100 degrees with low humidity is probably OK, but if it’s high humidity it may be best to withdraw. I would also think that how acclimated your horse is to hot weather is a factor as well. If it’s usually 80 degree highs, and this is an out of the ordinary event, then I’d be extra cautious as it’s going to feel EXTRA hot for your horse, but if your horses are used to 100 degree days, then it might not be such a big deal.

Other things to consider are if you have easy access to hoses with cold water to cool your horse off, if there will be shade available to hide under while you’re waiting, and the length of time you’ll actually be doing strenuous exercise. Low level dressage and jumping isn’t going to be as taxing as 3* XC for example (both in the warmups required and the actual competition). At the very least though, I’d definitely brush up on recognizing symptoms of heat stress in horses (and people!) though.

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I think the answer to this depends on what the temps are typically where you are.

Are the temps pretty normal for your part of the world this time of the year and do you typically ride at these temps and the horse handles it OK?


Hm looks like it’s about 38% humidity right now so that’s low. But where horse lives the weather is very inconsistent- foggy 55 degrees now, over 90 degrees last weekend. Otoh horse seems to handle heat well.

Well, my ride times are early which is great. I think we’ll be fine

Two weeks ago the temperature in the PNW was over 100 for several days over a weekend when a recognized event was taking place. These temps are definitely NOT normal for our area and personally, I would have scratched. Our horses are used to mid-70s to mid-80s, not triple digits. Myself, I get nauseous if I have to be out in the blazing sun for any length of time.

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I typically operate within this guideline - individual horse and climate pending - add the temperature and humidity together - if the number is over 150, monitor carefully.

I had an XC schooling today with my TB who is fit for Training level and lives out 24/7. The temperature was 91F, and the humidity 84%. This is a bit hotter than normal for my area where summers average 60-81F, but we’ve had several weeks of this weather and he is acclimated.

After a long walk warm up in the shade with limited trotting, I pulled him up after the fourth fence. He just had no tap today. We’ll jump some other time.

I don’t think what you are asking is unreasonable if early in the morning, in the shade, and the horse is fit – but it’s worth monitoring the horse to be safe.


A very smart friend of mine uses the heat index as a guide. As I understand it, the heat index is NOT a simple addition of temp and relative humidity. I’ll try to link to a calculation later but the TV weather seems to always discuss it.

Her rule is that if the heat index is above the normal body temp of horse or human, consider shelving your plans because it won’t be possible to dissipate heat resulting from exercise. A good breeze, shade and rapid application of cold water can modify her decision.


If the ice in my wine is melting really fast it is too hot to ride. Or if the puddle beneath the wine is really big.

No, but seriously… I kinda hate the relative humidity plus temp rule. You end up in weird situations where it it’s cool and a little humid but your are still at that point where you should be “using caution.” I really feel that Dew Point is a better indicator of how quickly my horse is going to cool down and how we are going to handle the heat. If it’s nearing 70, it’s seriously disgusting out.


I just presume that July and August are too hot for any serious riding after 8 am. June and September are sketchy too. Evidently I’m intuitively following the temp plus humidity guidelines. 90 plus degrees 90 plus percent humidity is the norm here.

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I would go for it. If your horse is fit, your ride times are early and the humidity is that low I think you both will be just fine.

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Right now is a perfect example. It’s 65 degrees but the relative humidity is 93%. According to the article above, “When the comfort index exceeds 150 and the humidity is greater than 75 percent, heat dissipation may be an issue and riders should monitor their horses carefully.” But it’s 65 degrees. My horse is barely going to sweat. Now, the dew point is 63 degrees, which is a bit humid but not ridiculous. Definitely comfortable to ride in.

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In real work, it would be one of those “monitor and adjust based on your horse”, which is really what the article is saying - the article is discussing race horses and performance horse work.

If you’re hacking down the trail? Not an issue.

We’re in the same area and I just came back from an early morning gallop set. It was 63F, 97% humidity. Same horse as above, and he was definitely a bit slower to recover in between intervals than he is on a day with less humidity.


Thanks all - it was 95-100 all weekend with a humidity around 25%. Horse appeared relatively unbothered, didn’t sweat excessively, and came 2nd in both her divisions!

I on the other hand was too darn hot - all the time. Luckily there was a cool river right there and I was right in it multiple times. This from someone who distrusts open bodies of water :sweat_smile:


Yeah, the problem with this is that hot air can hold more moisture. So 90 degrees and 60% humidity is a lot more disgusting than 70 degrees and 60% humidity. Which prompted me to Google relative humidity " the amount of water vapor present in air expressed as a percentage of the amount needed for saturation at the same temperature." So if they reported relative humidity consistently, that would be better to add to temperature. I wonder what could be done with dewpoint as well…