The National Weather Service (NWS) issues watches and warnings all across the United States to warn people of impending, dangerous weather.
Why do I care? Understanding the National Weather Service's system of watches and warnings will allow you to be better prepared for changing weather conditions.
The following is an explanation of watches/warnings/advisories issued by the National Weather Service that are common for the Southeast. Their website can be found at www.nws.noaa.gov. In general, watches mean that conditions are favorable for the development of severe weather but it has not actually been observed yet. Watches are issued to provide guidance to citizens before the onset of severe weather. Warnings are issued when severe weather has actually been observed, and you should take immediate steps to protect yourself, your family and your property from the severe weather that is approaching. Keep in mind that severe weather can occur even when there are no watches or warnings issued due to rapid changes in atmospheric conditions, so you should always keep a weather eye on the local conditions and be mindful of places you can go for refuge from the severe weather.
Tornado Watch- At the time that a tornado watch is issued, it may be sunny and nice outside. It can be several hours before you finally begin to see some stormy weather in your area. When a tornado watch is issued, conditions are favorable for severe thunderstorms (usually supercells) to produce tornadoes.
Tornado Warning- When a tornado warning is issued, either a tornado has been spotted on the ground or Doppler radar indicates a tornado. Tornado warnings should not be taken lightly, and if you are in an area that is under a tornado warning, you should try to take cover immediately.
Severe Thunderstorm Watch- A severe thunderstorm watch indicates that conditions are favorable for the formation of severe thunderstorms. Much like a tornado watch, conditions may be nice and sunny for the area at the time it is issued.
Severe Thunderstorm Warning- A severe thunderstorm warning means that the area is experiencing or will be shortly experiencing severe thunderstorm conditions. Those conditions include wind speeds of 58 miles per hour or greater and/or hail that is one inch in diameter or larger. It should be noted that lightning or rainfall are not included in the warning criteria for a severe thunderstorm. If a tornado is spotted or indicated on radar, the severe thunderstorm warning will be upgraded to a tornado warning.
Flash Flood Watch- A flash flood watch is issued when conditions are favorable for flash flooding to occur. Sometimes, an area that has a flash flood watch issued has already seen a lot of rain in a short amount of time, and more rain is expected to fall and lead to flooding conditions.
Flash Flood Warning- When a flash flood warning is issued, that means that flash flooding is occurring or is imminent. Flash flooding can occur just about anywhere, including streams, roadways, and even big cities. Generally, low lying areas are most prone to flash flooding, so move to higher ground if a flash flood warning is issued for your area. Flash flooding can also occur outside of where the rain is falling as streams and riverbeds downstream of the storm can rise quickly.
The thresholds for frost and freeze advisories, watches and warnings vary across the Southeast depending on the particular area's growing seasons. Here are some general examples of the advisories and warnings that are likely to be disseminated from the National Weather Service:
Frost Advisory- Frost advisories are issued when temperatures are expected to be near or just above freezing with conditions favorable for frost during the growing season. It is possible that tender vegetation and plants could be harmed by the frost.
Freeze Watch- When temperatures at or below freezing are possible during the growing season for a region, a freeze watch is issued. Freeze watches can be issued up to a day in advance so farmers and growers can prepare for the cold conditions.
Freeze Warning- Freeze warnings are issued when temperatures are expected to be at or below freezing during the growing season. Precautions should be made to any vegetation that is sensitive to the cold as a freeze could harm or kill them.
Winter Storm Watch- Winter storm watches indicate that intense winter weather conditions are expected within the next 12-36 hours. The criteria for a winter storm watch include heavy snow, sleet, freezing rain, or any combination of these three. Given the lead time on these watches, it allows people to prepare and anticipate the expected wintry conditions.
Winter Storm Warning- A winter storm warning means that significant winter weather conditions (mentioned in the watch) are occurring or will happen very shortly. Winter storm warnings can last for several hours due to the size and nature of winter storms.
Winter Weather Advisory- A winter weather advisory is usually issued when winter weather is expected, but the snow, sleet, and/or freezing rain accumulations do not meet the warning criteria, i.e., the conditions in your area are not expected to be hazardous or life threatening.
Tropical Storm Watch- A tropical storm watch is issued when tropical storm force winds (39-73 mph) are expected within the next 36 hours. These watches give people a good amount of time to prepare and plan in advance for the incoming tropical system. If tropical storm conditions are expected inland, an Inland Tropical Storm Watch will be issued for areas that could be affected (same color on the chart as Tropical Storm Watch).
Tropical Storm Warning- Tropical storm winds (39-73 mph) are expected within 24 hours or less. A watch is usually issued before a warning; however, if the storm changes track and begins to head inland somewhere, a warning could be issued immediately. If tropical storm conditions are expected inland, an Inland Tropical Storm Warning will be issued for areas that will be affected (same color on the chart as Tropical Storm Warning).
Hurricane Watch- Much like a tropical storm watch, when a hurricane watch is issued, hurricane-like conditions and winds (74 mph and above) are expected within the next 36 hours. If the hurricane force winds are expected past the coast, an Inland Hurricane Watch will be issued for areas that could be affected (same color on the chart as Hurricane Watch).
Hurricane Warning- Hurricane-like conditions and winds (74 mph and above) are expected within the next 24 hours or less. Hurricane warnings do not just depend on wind speed alone. If the storm surge is still very high after the hurricane has passed, the hurricane warning will remain in effect even if the winds are less than hurricane strength. If hurricane force winds are expected inland, an Inland Hurricane Warning will be issued for areas that will be affected (same color on chart as Hurricane Warning).
Links to National Science Education Standards:
Earth Science: EEn.2.5.4 : Predict the weather using available weather maps and data (including surface, upper atmospheric winds, and satellite imagery).