Todays high/low

I am a little puzzled about Todays High and Todays Low. What do they actually mean? It has been -20 C to -25 C for a couple of days in Lulea, Sweden and today it is around -15 C. Todays High has been -14,2 and Todays Low has been 12,2 all the time, despite the fact that it has never been warmer than -15 C … It does not make sense!