Fact is, you cannot tell your Apple Watch that wind or noise around you is not affecting your hearing, because you are wearing protection or, as in your case, a helmet.
When you open the Noise App on your Watch, then tap on “Learn More”, and scroll all the way down (or alternatively in the Apple Watch App on iPhone > Noise), you will see the following note:
”Water or wind can affect the accuracy of sound levels. […]”
Having said that, there is a way to mute these notifications temporarily:
Once you receive a Loud Environment notification, scroll down while the notification is focussed and select “Mute for 1 Hour” or “Mute for Today”.
Otherwise, you can mute Noise Notifications entirely by going to Apple Watch App on iPhone > Noise > Noise Threshold and selecting “Off”.
Hope this cleared up some things!
Kind regards,
MRXSurfer