If the comparison is winter temperatures, rather than year-round averages, it would make more sense to compare the coldest month (otherwise you mix together the effect of cold winters and cool summers, which are very different experientially). Helsinki has colder winters than Whittier does, though not by a huge margin. Whittier's coldest month is January, with average high -0.4 C (31 F) and average low -5.1 C (23 F). Helsinki's is February, with average high -1.9 (29 F) and average low -7.4 C (19 F). Whittier has a lower year-round average because it has cooler summers (highs around 60 F / 15 C, versus Helsinki's ~70 F / 20 C).

Helsinki is a pretty temperate city for Finland, though, being on the southeastern coast. Oulu and Tampere are a lot colder!