For PATH, it’s best to keep an eye on their Twitter account.

If ice does turn out to be an issue, you won’t find out until they start cancelling trains. They’re not going to give people much advance notice because the conditions are too unpredictable.

For what it’s worth, PATH seems to be pretty reliable during winter storms except when there’s heavy snowfall and snow drifts impacting the outdoor tracks. Even then, they are usually back to normal within a few hours.