Record temperature during activity.

There are weather stats on GC, but for temperature I have a Garmin Tempe (it's dirt cheap) I affix to my shoes and get a much more accurate temperature for the whole of the run.

Not sure about humidity though.

On GPS activities you get the weather data of the acclivities beginning displayed on the top right corner of the map (in Garmin Web).

Not really useful for long tours your start in the morning when its still cold, but ok for short ones during the day.

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It already does that.

The heat acclimation widget takes the weather into account, and the temperature and wind speed is displayed on the map of your activity in Garmin Connect (GPS activities only).

When the OP says “to record” I guess is referring to local temperature and humidity.

On that regard, as already stated, Yes for temperature with a Tempe sensor. No for humidity (the watch has no igrometer, not any external sensor).

On acclimation that’s a long standing issue, discussed many times. It takes weather data from nearby airports which in my case it often means at altitudes several hundred meters below. In essence: temperature and humidity is often totally bogus, and so heat acclimation as well.

Actually it gives you a temperature and humidity but I was looking for it at the start of an activity and at the end my temperature could be 10 to 20 degrees difference from the start of a run to the end of a run.

Today's run my outside temperature says it's 70° with 18% humidity and the map says it was 61° 27% humidity