How reliable are the weather forecasts? Based on data collected from one hundred and thirteen cities in the United States over 38 months on three variables, maximum temperature, minimum temperature, and Precipitation, accuracy of the weather forecasts was examined. The same day forecast has been extremely accurate, especially for the maximum temperature, while the forecast errors and variability increase as we go further out in days forecast. Some cities have larger or smaller forecast errors compared to others. For long-term weather forecasts, the maximum and minimum temperature forecast errors has decreasing correlations overtime, respectively; However, the correlation between maximum and minimum temperature forecast errors is positive and increasing overtime. The 7-days forecast errors of precipitation are pretty accurate.