If the ground is frozen more than a few inches, forget trying, if you do, wear goggles if you use any type of tool to "chop" through. If you live near the ocean, you can always try it in the wet sand as the tide is going out, that would not be frozen. If you have woods nearby with decent amount of ground leaf coverage, the possibility exits it is not frozen hard underneath the leaves, or look for a southern facing slope, they usually defrost first. Forget fields that are shaded if it is below freezing often in your area.
Usually frozen ground does not stop me in the woods, usually can break thru with my sharpened dry wall hammer, if the frozen crust is only an inch or two. But when the white stuff covers the ground, and stays, I'm done until a warmup and it melts to expose bare ground.
The past two winters here in Southern NJ have been the pits for getting out and detecting, not had two years in a row like this in quite some time.
Attached a photo of the dry wall hammer my son and I both use, its long solid narrow shank allows for good, deep depth on cutting thru the frozen turf and great for slicing through roots in the woods. Would never recommend this for a park, sure it would raise some eyebrows.
Don