It may be that the home's energy consumption isn't actually higher than usual, but that your bill covers a longer period of time. Compare the number of days in the billing period to that of previous bills. Remember to include the costs for the daily system charge AND the additional energy used during those extra days. In most cases, your previous, or following, bills will be lower than expected.
Also, look to see if the bill was "estimated". This means weather or unforeseen circumstances forced PUD 3 to estimate the bill based on historical usage. The following month's meter read will ensure the bill will get back on track. For billing questions, please contact customer service at (360) 426-8255.