"Where is snow?"
Translation:Hol van hó?
I think the original word had a -v- in it (perhaps something like "hav") which survived in the plural ("havak") but in the singular, "hav" turned into "hó" as the final consonant merged with the vowel.
Similar with e.g. kő "stone", plural "kövek" or ló "horse", plural "lovak" where a final -v disappeared in the singular but remained in the other forms.
Greek has similar things as well, e.g. -ματ turned into -μα which is why we have "enigma" but "enigmatic" or "stigma" but "stigmata"; and Slavic has this e.g. in nouns for young animals where a final -t was dropped in the base form but kept in the forms with endings, e.g. Ukrainian теля "calf" but plural телята.