Develop a multiple regression model with categorical variables that incorporates seasonality for forecasting the temperature in Washington, DC, using the data for the years 1999 and 2000 in the Excel file Washington DC Weather. Use the model to generate forecasts for the next nine months and compare the forecasts to the actual observations in the data for the year 2001.

Washington DC Average Temperatures Month Year Temp January 1999 34.9 February 1999 37.5 March 1999 41.4 April 1999 53 May 1999 62.8 June 1999 70.8 July 1999 78.5 August 1999 75.4 September 1999 67 October 1999 53.1 November 1999 50.1 December 1999 38.2 January 2000 32.7 February 2000 36.8 March 2000 48.2 April 2000 53.6 May 2000 64.8 June 2000 72.3 July 2000 72.1 August 2000 73 September 2000 65.2 October 2000 57.2 November 2000 42.9 December 2000 28.1 PREDICTIONS January 2001 February 2001 March 2001 April 2001 May 2001 June 2001 July 2001 August 2001 September 2001 Actual Actual - Predicted 32.3 38.5 36.2 55.5 60.8 69 72.2 64.1 65.3 Washington DC Average Temperatures Month Year Temp January 1999 34.9 February 1999 37.5 March 1999 41.4 April 1999 53 May 1999 62.8 June 1999 70.8 July 1999 78.5 August 1999 75.4 September 1999 67 October 1999 53.1 November 1999 50.1 December 1999 38.2 January 2000 32.7 February 2000 36.8 March 2000 48.2 April 2000 53.6 May 2000 64.8 June 2000 72.3 July 2000 72.1 August 2000 73 September 2000 65.2 October 2000 57.2 November 2000 42.9 December 2000 28.1 PREDICTIONS January 2001 February 2001 March 2001 April 2001 May 2001 June 2001 July 2001 August 2001 September 2001 Actual Actual - Predicted 32.3 38.5 36.2 55.5 60.8 69 72.2 64.1 65.3