In January the northern water areas of the continent are frozen and snow-covered; Hudson Bay becomes unduly cold, and the greatest southward bending of the isotherms is somewhat east of the continental axis, with an extension of its effects out upon the Atlantic; but the southward bending isotherms are somewhat looped back about the unfrozen waters of the lower Great Lakes.
With the exception of the Lysa Gora hilly tracts (Kielce and south Radom), which lie within the isotherms of 41° and 42°, Poland is situated between the isotherms of 42° and 46°.
The extreme range of the monthly isotherms crossing the state is from about 35° in winter to 81° F.
In summer, and the range of annual isotherms from about S4° to 60° F.
In the same midsummer month all the eastern half of the United States is included between the isotherms of 66 and 82; the contrast between Lake Superior and the coast of the Gulf of Mexico, 1200 m.