The basic difference between a weather watch and a weather warning is the immediacy of weather conditions. A watch is issued to alert people in a certain region, in advance, that conditions are favorable for dangerous weather. When certain meteorological circumstances are present, severe weather can develop quickly, and watches are issued to prepare people for this possibility so they can take appropriate safety measures. One can be issued for any type of severe weather, including winter storm and wildfire conditions, but most frequently involve severe thunderstorms, floods and flash floods, or tornadoes.
The simplest distinction is that a weather watch indicates possible severe weather, while a warning indicates that severe storms or the conditions that produce severe storms have been observed in nearby areas and will likely reach the location being warned. A watch does not necessarily mean that severe weather is imminent; it indicates that it is possible, and likely, due to existing or predicted atmospheric events or conditions. There are distinct guidelines for determining if a watch or a warning should be issued.
For example, a severe thunderstorm watch is issued if conditions suggest that winds may reach 55-60 miles per hour (about 88-96 kilometers per hour) or higher, or may produce hail that is 0.75 inches (about 1.9 cm) in diameter or larger. A severe thunderstorm warning, on the other hand, is not issued until such a storm has been physically observed or is spotted on radar. A tornado watch is issued when conditions may produce a tornado, and a warning is issued when a tornado has been sighted, or when rotation is seen on radar.
It is important for everyone to pay attention to weather alerts, to begin taking safety measures if conditions favor bad weather, and to prepare to take cover or move to a safer location immediately in case a warning is given. It is wise for a family to prepare a safety plan and conduct drills occasionally to make sure members know how to respond once a weather watch or a warning is issued. It is also a good idea to make a post-storm plan, and arrange a meeting place, so family members know where to look for each other if separated during a storm.