Heavy snow in Michigan and other northern states slowed the delivery of Christmas trees in the past two weeks, according to Associated Press.  An article today (link) noted that in some loading yards, stacks of trees awaiting shipment were covered by up to two feet of snow. The snow also covered roads and delayed transportation.  Prices may rise slightly in affected areas, but many other factors such as demand, transportation costs, etc. can influence the price consumers pay for the trees.

Source: Commons Wikimedia
Source: Commons Wikimedia