| 1 | The dividing line between the two air masses is called a front. | |
| 2 | On this front, let's contrast Brazil and the United States. | |
| 3 | Sometimes the air masses which meet at a front cause storms. | |
| 4 | Forecasters say an arctic front will bring even more startling snow tomorrow. | |
| 5 | When this happens uniformly across a large front, a roll cloud may form. |