The last days in Poland are particularly cold compared to the average winters of the last decade. Really - they are exactly as cold as they shall be by January.
A few thoughts from an insider:
Put on your down jackets and not too many layers between the jacket and your body.
Choose tea, choclate or coffee over the 3rd mulled wine.
Eat fat.
Entering a warm room or a car, open your jacket and let the warm air touch your inner layers and fill the down jacket.
-18°C is 0 °F, which is as much as in your freezer, and it is quite endurable.
Expose yourself to the sun; the sun warms immediately.
Days are short!
Walk, move - don't freeze, enjoy!
Do not play hard, wear a hat and a scarf and gloves.
2 fingered gloves are better than 5 finger gloves
You will feel better at -10°C or 15°C than -1°C. The air will be dry and pleasant. - 27°C is already really rough.
The colder it is, the fewer clouds there. During the day, it is simply sunny. Cloudless night sky causes the temperatures to drop sharply into the -25 Celsius zone. Which is dangerous.
To experience extreme cold in Poland, you need to go either to the most north-western part around Suwałki or venture out to the south into the valleys between the Tatras and Gorce mountains. The Orava-Nowotarska Basin (Kotlina Orawsko-Nowotarska) and its peat bog depressions are among the coldest places in Poland. This region is known for extreme winter temperatures, often dropping below -40°C in localized areas like the peat bogs near Zubrzyca Górna. The unique geography—such as the basin’s shape and lack of wind—creates "cold lakes" where frigid air pools, making it a fascinating (if challenging) destination for adventurous travelers. Over there, I would never stop the engine of my diesel car and pour the better, more temperature-resistant fuel before. There are special additives available at local petrol stations, too. A gasoline-powered rental car is also a good option.
Ice is always tricky, so walk on thick ice with caution.
Iced rivers are deadly traps. Lakes are not that deadly.