It was cold yesterday, much colder than it has been for ages. I went out for a bike ride in the afternoon, and actually needed to work harder just to stave off the chill. Then Erika mentioned that she thought that it was one of the frozen saints' fault.
The frozen saints "Fagyos szentek" are Pongrác, Szervác, and Bonifác (and possibly Orban). I'm still trying to work out what those names translate as in English, without much success, but since they're Saints, they must have equivalents - Bonifác is, I believe, "Boniface" and Orban "Urban" but I have never heard of anyone actually called these names, so probably Pongrác and Szervác are even more obscure.
Their relevance to the weather is that in May there are 3 or 4 days which are (according to folk wisdom) always cold - and in fact it is advised that you don't put your crops/plants that could be damaged by frost out until after the last of them has been and gone. These days are the saints days of Pongrác, Szervác, Bonifác, and Orban. But having done a bit of checking it seems like the first three are actually May 12th, 13th and 14th (ie not yesterday but this weekend). More details (in Hungarian). Orban is on the 25th.
So now you know. If tomorrow is cold it's the fault of that bloody St. Pongrác. Who, having done a bit more googling, seems like he might actually be St. Pancras. One of those saints (perhaps the only one) who is more commonly known as the name of a railway station. In fact, until that moment I hadn't stopped to consider that there was someone around once who was called Pancras. Amazing what appears when you start aimlessly looking stuff up.