The link below will open an annimation of the 500 mb height pattern over the last 24 hours. Use the buttons at the top of the annimation to stop the loop and step through individual images. At this point try to familiarize yourself with these maps. Can you identify large-scale troughs and ridges? On these maps the contour lines are labeled in decameters (a decameter is 10 meters). For example, the line labeled 552 means that everywhere on the line, the height of the 500 mb pressure surface is 552 decameters or 5520 meters above sea level. What can you say about the large-scale temperature pattern across the United States based on these contour maps?