I have noticed some difference due to weather. When summer gets into full swing in the Northeast and we get long stretches of very humid days, I find that the pipe handles differently. High humidity will produce a similar effect as smoking tobacco with a higher moisture content. There is moisture in the tobacco (typically around 12%, but varies depending on the blend and how you store it and whether you dry your tobacco, etc). That moisture, along with any water vapor formed as a combustion product, and any moisture already in the air, winds up in your "smoke." If you don't store your tobacco in air-tight containers, the tobacco will readily pick up additional moisture from the humid air and make the differences even more pronounced.