Why is it that New York City has a greater temperature range than Eureka, CA even though they are at the same latitude ?

New York has a different geographical setting and location.

Explanation:

Most of New York is dominated by a geography which consists of farms, forests, rivers, mountains, and lakes. Eureka, California has a geography which consists of fertile farmlands of the Central Valley and the arid Mojave Desert. The geography of a place affects the climatic conditions such as temperature, precipitation etc.Areas with deserts will experience little rainfall and areas with rivers will experience high rainfall.

Another point is that the temperatures vary greatly because they have a different position on Earth. One is on the east coast and the other is on the west coast. Temperatures will be influenced by the position Earth has towards the sun and the axis angle.