A cold air pool is a low pressure system, that only exists in the upper troposhere. The two figures above are an example and show, that the low pressure system is only evident in the 500 hPa weather chart (right figure) and not in the surface weather chart (left figure). Cold air pools are a challange for the weather forecast, because the numerical weather prediction models cannot predict the exact direction of movement. As the cold air pool only exists in the free atmosphere, it is uncoupled from influences from the ground as friction. The cold air pool is often related to bad weather. On its front the weather phenomena are comparable to a cold front. The back side is similar to a warm front. Since the air aloft in a cold air pool is quite cold, its air mass is unstable. This often leads to shower and thunderstorms. As the low pressure of a cold air pool only exists aloft, the barometer often indicates nice weather.