Jan Mayen does have very cold weather throughout the year. Even in Early June, 2005.
In March, the weather is amazingly bitterly cold. Remember to wear warm clothing there if you have a chance to go there.
That sort of bitterly sub-zero weather gradually stopped in Late May, but even in summer, it rarely warmer than 10C even during daytime. Windchill is severe even in Summer.
Rainfall(Summer): Rarely heavy downpour, but usually damp and cold, like New Brunswick or Maine in late fall or spring.
Snowfall(WInter): Sometimes very heavy, usually during springtime.