I have to post this because the only existing answer is misleading. Here's a more relevant NGram...
The reality is native speakers don't often say it's hailing/sleeting, even allowing for the fact that hail and sleet are less common that rain and snow. If you ask someone on the phone "What's the weather like?", they're more likely to reply with some alternative to avoid using those words as verbs - for example...
There's a hailstorm right now, or
It's snowing - well, more like sleet, actually.
That's not to say hailing or sleeting would mark you out as a non-native speaker - but it certainly wouldn't encourage people to think you are one.
As for graupeling, I would suggest that's a virtually unknown German term. Speaking as an Englishman, obviously I talk about the weather all the time, but I didn't even know the word until now.
EDIT: I originally answered because the earlier answer used a misleading search term (as an isolated word, hailing is far more likely to be used to mean calling, so most instances are "false positives"). Obviously the main reason for different levels of usage is hail is uncommon relative to snow and rain.
Possibly because it's relatively uncommon (in UK SE we only get a few hailstorms a year, that rarely last long), I perceive it hailed earlier as very slightly "marked" compared to there was a hailstorm earlier. By the same token, I myself would tend to say "There was thunder" rather than "It was thundering".
The verb forms to hail (and perhaps to a lesser extent to sleet) aren't particularly unusual. In fact they're probably used more often in creative fiction than actual weather patterns would justify, for the sake of atmospheric effect. The "strangeness" of using these verbs in speech may depend on local climate.
The reason hailing may be less common than raining or snowing is that hail does not fall as frequently as rain or snow. However, saying, "It's hailing." sounds very natural to native speakers. Personally, I have never heard anyone say, "It's sleeting." I never heard of graupel until reading the above question. Most of the people I know would probably call it hail.