Characteristics
Near the surface, warm dry air is less dense than warm moist air of lesser or similar temperature, and thus the warm moist air wedges under the dry air like a cold front. At higher altitudes, the warm moist air is less dense than the cooler, drier air and the boundary slope reverses. In the vicinity of the reversal aloft, severe weather is possible, especially when a triple point is formed with a cold front. The dry line is most common in the spring. Its location is close to the location of the 55 °F (13 °C) isodrosotherm, or line of equal dewpoint. The location of the dryline may not be marked with a surface pressure trough or shift of the wind direction. It bulges more to the east underneath the location of the highest winds within the jet stream. While dry lines are most common in the Great Plains, northern India also witnesses a similar moisture boundary. In northeast India, it occurs mainly before the onset of their summer monsoon, while northwest India experiences it during the monsoon season.
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