The surface map above shows weather observations shortly before 10:00 p.m. this evening. It is a little difficult to read the plots because of the small font. Look at Omaha, Nebraska. The plotted ceiling height is C31 which is code for 3100 feet above ground level. The sky is overcast. If you look at the station model plots and observation coding which are accessed on our home page you will see the Omaha sky is overcast.
Now, look at the chart below. This is the radiosonde (weather balloon) plot from Omaha, Nebraska as of 6:00 p.m. local time. The red line is the temperature in degrees F while the green line is the dew point. wherever the lines are close together the relative humidity is high and the probability of cloud cover increases. On the far left the chart shows conditions are favorable for cloud formation - see the small gray boxes at the left side of the chart. You can see a small gray box on the left side marking the 3000+ altitude. This confirms a layer of low level moisture that is creating the overcast skies at Omaha. Notice that the layer is less than 2000 feet thick. Above it the red and green lines diverge indicating a deep layer of dry air. There are several layers in which clouds are also possible - see if you can find them. These areas indicate the possibility of up to 3 layers of moisture that may be producing cloudiness.
What does the instrument package look like? Learn more by clicking here.