Muscle cramps are a very common problem. In the lower back, they tend to be caused by muscle strain
or by relative weakness or imbalances in the paraspinal back muscles, which are the muscles that run up and down both sides of the spinal column.
The common triggers form muscle cramps include poor posture (think for example of sitting stooped in front of a computer screen), heavy lifting, and intense physical exercise. Additionally, many people do report that cramps can be worse in cold weather. Why this is exactly is not totally clear. In part it may have something to do with the fact that we tend to be less physically active during cold weather, which could worsen muscle stiffness and decrease flexibility.
If you find that you are having persistent muscle cramps or low back pain, this is something that you should talk to your primary care doctor
about. In addition to giving you advice about what medications you can take to help with the pain when it occurs, they can also give you advice on some stretching exercises and back muscle strengthening exercise which might help to prevent further episodes of cramps down the road.