This paper presents the behavior of two warm fronts which affected the weather in Rio Grande do Sul state. Satellite images and various meteorological fields were analyzed for both situations. In the first one the system moved from Argentina and gradually reached the various regions of the state, from the west to the east. During the passage of this system, occurrence of precipitation was registered; in some stations of the shore, cumulonimbus clouds were observed. During about 24 hours the Rio Grande do Sul state was under the influence of that system. In the second case, the warm front that reached the same state was not associated with a clearly defined vortex. In the second situation, a warm front arrived at state mentioned earlier, while the vortex to which the front was associated, was still over the Pacific Ocean. For this case, vertical sections of potential temperature were constructed and it was observed a slope of the isentropic surfaces, which is related to the presence of vertical motions. The mesoscale analysis showed that there was a region with higher pressures in the northeast region of Rio Grande do Sul and lower pressures in the west/northwest. Also in this second situation cumulonimbus clouds were observed in various stations of the state, including some in the west part of the state. It was also registered the occurrence of fog during the two situations.
warm fronts; frontal systems; weather forecasting
