Heavy snow or rain can curtail logging in any area. This disruption will affect the amount of logs that are available to be milled. If market prices are suppressed due to demand, mills will curtail operations to reduce inventory backlogs at the mill. If timber is scarce, mills will have no need to increase production capacity. If production capacity is static, lumber prices will rise when demand isn't met.
Housing starts make the highest impact on lumber demand.
The number of housing permits issued can predict which way housing starts are headed. Softwood prices will be the first to be effected because of its structural use in home building. Hardwood prices lag by another 6 months. This is due to hardwood being used in flooring, molding, trim, and furniture - the latter stages of new home completions and furnishing. There is an industrial demand as well.