Knowing The Difference
- A WATCH is used when the risk of a hazardous weather or hydrologic event has increased significantly, but its occurrence, location, and/or timing is still uncertain. It is intended to provide enough lead time so that those who need to set their plans in motion can do so.
- A WARNING is issued when a hazardous weather or hydrologic event is occurring, is imminent, or has a very high possibility of occurring. A warning is used for conditions posing a threat to life or property.
Or to put it in laments terms, a WATCH means that the potential exists for the development of severe thunderstorms or tornadoes, depending upon the specific type of watch. With a watch, conditions are favorable for severe thunderstoms/tornadoes to form but no guarantee - be vigilant. In the case of a tornado watch, this DOES NOT mean that a tornado has been seen or even indicated on radar...it just means that conditions are favorable for the formation of tornadoes in thunderstorms. Similarly, a severe thunderstorm watch means that conditions are just conducive for the development of severe weather, and DOES NOT indicate that severe weather has been reported. While no immediate action on the part of the general public is required for the issuance of a watch, citizens should keep up to date on the current weather situation and be prepared to seek shelter if necessary.
A WARNING means a severe thunderstorm/tornado has been detected by radar and/or spotted - take appropriate precautions or take cover now. Warnings requires more immediate action and should be taken seriously. A severe thunderstorm warning indicates that severe weather is imminent in your area or is already occurring (based on either human observation or doppler radar). Specifically, a tornado warning means that a tornado has been either spotted by a weather observer or indicated by dopplar radar.
Ok lets break them down individully and give you an example of what a Storm Prediction Center Watch box looks like, and what a severe warning and tornado warning look like on radar.
SEVERE THUNDERSTORM WATCH: A severe thunderstorm watch means that atmospheric conditions are favorable for severe thunderstorm development. The severe thunderstorm watch outlines an area where an organized threat of severe thunderstorms is expected generally during a three- to six-hour period. Severe thunderstorm watches are issued by the Storm Prediction Center after consultation with local National Weather Service offices and can cover several counties to several states at a time.
During a severe thunderstorm watch, it is important to think about where you will be during the lifetime of the watch. If you are outdoors, develop a Weather Ready plan that includes directions to the nearest lightning and hail-proof shelter. Keep in mind that severe hail has the ability to smash car windshields, cause injuries and, in the extreme, punch holes in roofs.
SEVERE THUNDERSTORM WARNING: A severe thunderstorm warning means that a severe thunderstorm is imminent: It is occurring or is about to occur. Severe thunderstorm warnings are issued by the local National Weather Service office when it deems a particular thunderstorm has met, or will soon meet, the severe criteria listed above. Severe thunderstorm warnings are usually highly localized – covering parts of one to several counties – and generally last for 30 to 60 minutes.
During a severe thunderstorm warning, it is important to get to safety immediately. Severe winds – gusts of 58 mph or greater – can down trees and power lines, causing injury and potentially death to those hit by large falling objects and other debris. In addition, if a severe thunderstorm is producing large hail, injury and significant property damage can result.
TORNADO WARNING: A tornado warning means that a tornado is imminent: A tornado is occurring or is expected to develop. Tornado warnings are issued by the local National Weather Service office when any of the following occurs:
Doppler radar indicates strong rotation within a thunderstorm. Dual-polarization Doppler radar detects a tornado debris signature, indicative of lofted debris from a tornado. Trained storm spotters have reported a funnel cloud (a circulation aloft not yet in contact with the ground). Trained storm spotters have reported a fully-formed tornado (the circulation has made contact with the ground).
This is an example of a tornado warning polygon.
Tornado warnings are usually highly localized – span parts of one to several counties – and generally last for 30 to 60 minutes.
During a tornado warning, it is important to get to safety immediately. Strong to violent tornadoes can level buildings and loft vehicles into the air. Even weak tornadoes can cause damage to roofs and other structural damage, causing injury and potentially death to those hit by large falling objects and other debris.
- A watch supercedes a warning
- A watch or warning means that severe weather is definite.
FALSE. This misconception also stems from the Powell and O’Hair study which discovered that when some people hear the term watch or warning, they assume severe weather is “definite” whereas, in actuality, the thunderstorm or tornado may only affect some small portion of the watch or warning area. With a watch, the coverage area can span several counties or even stretch across several adjoining states. In some instance where organized severe weather "outbreaks" are expected to occur, a watch can cover about 25,000 square miles, or about half the size of Iowa. However NOT every county or state within the watch will necissarily experience severe weather. Warnings work in much the same way. A warning may also be issued for a portions of a county or several counties if near the county borders. However the tornado, whether confirmed by spotters or radar indicated will not necissarily hit every location within the warning. In the event of a tornado warning, a tornado is likely (but not definitely) near you. it is important to pay attention to your local news Meterologist or a weather alert radio. They will outline the areas to be affected by a storm or tornado, tell you the direction it's traveling, and the next areas to be impacted including cities and mile markers along highways or interstates.
- A tornado warning means a tornado is on the ground
Not necissarily. This isn't necissarily always the case 100 percent of the time. Most tornado warnings are actually issued because a storm's rotation is strong enough to be picked up by radar (radar confirmed.) In these instances, the storm's rotation is strong enough to warrant a warning even if a tornado is not on the ground. In fact, the majority of tornado warning are issued because of radar indicated roation, not because a tornado has been spotted.
PDS Watches: What are they?
The last thing we are going to talk briefly about is what is known as a PDS watch. It is something that many of you may not be familiar with. A PDS watch can be considered one step above a normal watch and is usually only primarily used for hightened tornado watches. PDS stands for "Particularly Dangerous Situation". A PDS watch is basically a type of enhanced wording first used by the Storm prediction center for tornado watches and eventually expanded to use on warnings. It is issued at the discretion of the forecaster composing the watch or warning and implies that there is an enhanced risk of very severe and life-threatening weather, usually a major tornado outbreak or when long tracked violent tornadoes are expected to occur.
PDS tornado watches are issued when there is a higher than normal risk of multiple strong to violent tornadoes, especially those that are predicted to be long-track in nature, with path lengths of more than 20 miles or within the watch area usually amounting to damage consistent with EF-4 or EF-5 tornadoes. This enhanced wording in a tornado watch is meant to alert the public of the potential for very life-threatening severe weather. While there are no set criteria for a PDS watch to be issued, they are usually issued when the potential exists for a major tornado outbreak. PDS Tornado Watches are often issued on Moderate or High risk days for severe weather. A PDS watch while normally reserved for these hightend tornado watches, can also be issued with severe thunderstorms (usualy when a long lived derecho event is expected), or when severe flooding is expected. However these type of PDS watches are rarely issued.
In the event of either a watch or a warning it is important to remeber to stay calm and do not panic. Monitor the weather conditions in your area and have your severe weather prepardness plan ready.