<P> Polar lows are mesoscale weather systems, typically smaller than 1,000 km (600 mi) across, found near the poles . Like tropical cyclones, they form over relatively warm water and can feature deep convection and winds of gale force or greater . Unlike storms of tropical nature, however, they thrive in much colder temperatures and at much higher latitudes . They are also smaller and last for shorter durations, with few lasting longer than a day or so . Despite these differences, they can be very similar in structure to tropical cyclones, featuring a clear eye surrounded by an eyewall and bands of rain and snow. . </P> <P> Extratropical cyclones are areas of low pressure which exist at the boundary of different air masses . Almost all storms found at mid-latitudes are extratropical in nature, including classic North American nor'easters and European windstorms . The most severe of these can have a clear "eye" at the site of lowest barometric pressure, though it is usually surrounded by lower, non-convective clouds and is found near the back end of the storm . </P> <P> Subtropical cyclones are low - pressure systems with some extratropical characteristics and some tropical characteristics . As such, they may have an eye while not being truly tropical in nature . Subtropical cyclones can be very hazardous, generating high winds and seas, and often evolve into fully tropical cyclones . For this reason, the National Hurricane Center began including subtropical storms in its naming scheme in 2002 . </P> <P> Tornadoes are destructive, small - scale storms, which produce the fastest winds on earth . There are two main types--single - vortex tornadoes, which consist of a single spinning column of air, and multiple - vortex tornadoes, which consist of small "suction vortices," resembling mini-tornadoes themselves, all rotating around a common center . Both of these types of tornadoes are theorized to have calm eyes . These theories are supported by doppler velocity observations by weather radar and eyewitness accounts . </P>

Is the eye wall of a hurricane dangerous