Breakdown of Hvernig sem veðrið er, kemur hún alltaf í kennslustundina.
Questions & Answers about Hvernig sem veðrið er, kemur hún alltaf í kennslustundina.
Veðrið is the definite form of veður, so it means the weather.
That is the normal way to talk about weather in Icelandic, just as English also usually says the weather rather than just weather in this kind of sentence. Grammatically, veðrið is also the subject of er.