It can be argued that the most violent weather in the U.S. is related to spring time storms. The other prime candidate would be the strong hurricane, which may do far more property damage than a springtime storm. The thunderstorm may, in turn, cause a far greater loss of life than a hurricane. As pilots, we have to study storm systems at all times of the year, but it＇s in the springtime that we face the greatest challenge - simply because there are more storms and they are more violent. Clues we might use in other seasons take on new meaning in the spring. For any low-pressure system to develop and turn into a storm, it has to have upper-level support. A trough, or area of low pressure, aloft has to come along and aid and abet the development of a strong low at the surface. Often when conditions are turning up for a big storm the weather map will show several weak surface lows. One of those, the one that gets the proper upper-level support, will become the main event. Or a new low may form along a stationary front when conditions aloft provide the necessary support. Temperature contrast is one reason that springtime storms are often so strong. In the spring the air aloft remains cold, especially the air that moves down from over Canada, but the surface air is warming up and tends to become warmer earlier in the season than does the air aloft. Cold air over warm is the unstable condition, the upper-level support. How might even a southwesterly flow aloft be cold? It could be air drawn down from Canada that turned the tip of a trough aloft and then headed back toward the northeast，flowing over warmer air at the surface. It is that condition that creates a firecracker effect in the springtime atmo sphere. In the springtime, then, a strong southwesterly flow aloft - 500 millibars or about 18,000ft is the key level - means that conditions can become active. It doesn＇t happen every time but, on the other hand, severe storm activity doesn＇t often develop when the gener al upper level flows, is out of the northwest. There you have cold air aloft over cold air at the surface. Likewise, a straight east-west flows aloft doesn＇t suggest a high likelihood of severe weather. But there are always exceptions to meteorological rules of thumb. With those basics, which, hopefully, we all review before each spring flying season, let’s go flying.3. Springtime storms are very strong owing to .