It is usually very difficult to tell if a dog has a fever from touch alone, but you can tell if you take their temperature with a thermometer.  For more information about checking a dogs temperature for a fever, I recommend reading more about it here

https://pets.webmd.com/dogs/high-fever-in-dogs#1

As mentioned, if a dogs temperature is greater than 103 or higher it is a fever that should be further investigated.  If there is something like a storm making your dog nervous, this can certainly elevate their temperature as well.  If there are other signs such as loss of appetite, lethargy, vomiting or diarrhea, I would recommend you see a veterinarian straight away to get to the bottom of it.  Even if it is from just anxiety and this is happening regularly when there are storms, you should also consider talking to a vet about your environment and what you can do to help your dog feel more comfortable during storms.