Fares across the Atlantic have been low for a variety of reasons: too much capacity from the major airlines, low fuel prices that support this, and increased competition from low cost airlines like Norwegian and Wow Air.
AirfareSpot highlights fares to Europe starting at $281 but there’s a trick to get the pricing even lower.
Norwegian has their flights from New York JFK to Oslo, Copenhagen, and Stockholm on sale during low season of January through mid-March at a super deep discount. You can visit these cities when it’s cheap, or use these flights as a jumping off point to travel elsewhere in Europe. (I’m seeing Paris from $347, still a great deal and I actually like visiting Paris in winter.)