If you stop mowing the lawn because it stopped growing,

It might be suddenly Winter.
If you have trouble lighting the camp fire in the back yard,

It might be suddenly Winter.
If all the trees in your yard have a surprised look on their branches,

It might be suddenly Winter.
 
If you can finally see what your neighbors are doing,

It might be suddenly Winter.
If tonight's hotdog grillin' is canceled because you forgot to put stuff in the shed,

It might be suddenly Winter.
If you fell asleep on green grass and woke up on white,

It might be suddenly Winter.
 
If the last few birds look like they're panicing,

It might be suddenly Winter.
If you can take three different pictures, merge them into one and have them look like this,
It might be suddenly Winter.