In this video I explain how to create a forecasting model in Excel for a data set that involves both trend and seasonality. I chose not to deseasonalize data set before finding the trend parameters.
Dataset URL: Copy and Paste it into Excel or work in Google Sheets
https://docs.google.com/spreadsheets/...

I posted a follow up video in which you can handle multiple forecasts at the same time for multiple SKUs (Stock Keeping Units).
   • Seasonality and Trend Forecasting Vid...  

An alternative method could be to use a multiple linear regression model. And I think the regression model is more practical. Yes, I have recorded a video for that as well. The link for the video is    • Seasonality and Trend Forecasting usi...  

These videos are created for the students at The College at Brockport, State University of New York. However anyone can benefit from them as they should work for any Operations Management class.