Here's my $0.02 (offered at a $0.02 discount):
Strength in the front-month contract (particularly relative to the back months) is typically associated with a supply shortage. Strength in the back month contracts is generally associated with higher demand expectations.
Taking this VERY shaky theory one more step, "supply shocks" are more dramatic, but also shorter in length (think of a huge spike up, then a sharp recovery). "Demand" trends take longer to develop (and have more pullbacks), but could have longer "legs."
This could all be complete B.S., but now you have a hypothesis to test.