Avista’s Washington customers could see changes in their gas and electric bills starting Nov. 1, based partly on fluctuations in wholesale power costs.

The Spokane-based utility has asked the state Utilities and Transportation Commission to approve an increase in electric rates and a decrease in gas rates.

If approved, residential customers using an average of 66 therms of natural gas per month would see their monthly bills change from $61.85 to $58.81, a decrease of $3.04 per month, or about 4.9 percent.

Residential electric customers in Washington using an average of 957 kilowatt hours per month would see their monthly bills change from $83.91 to $86.19, an increase of $2.28 per month, or about 2.7 percent.

A portion of customers’ rates are adjusted annually based on changes in wholesale power costs and a credit from the federal hydro power system on the Columbia and Snake rivers. This year, the utility is also seeking to recover from the warmer winter, which led to lower electric and gas sales.

The adjustments are separate from Avista’s pending rate case. The utility is seeking approval to increase base rates in 2017.