Knowing a nuke was going to hit in the next few minutes wouldn't be much use to anyone.
I don't think there's anything sinister about this, just more nannying from the government. My phone has "extreme alerts" and "severe alerts" - whatever the difference is, and both are switched off.
They're going to use it to bombard us with "danger to life" messages when the temp hits over 75 degrees or there's more than 1/4" of snow on the ground.