What does a Watch or a Warning mean About the Weather?

max_weisenfeld

Last week with the tornado warning there was some conversation about the meanings of watches and warnings, so I would like to take a few minutes to discuss what the various things mean when used by the National Weather Service1 (NWS) and why they are used. 

Weather prediction is a science based on calculating immensely complex data sets forward in time.  As anyone who has tried to predict the location of a 3 year old 30 seconds after you told her to stay /right there/ can tell you, predicting complex motion into the future is not easy.  To follow the example, it is more likely that the toddler is still in the house than that she is outside, and more likely she is within a 100 yard radius than across town.  But the longer the forward time window, the larger the circle of uncertainty gets.  At some point, it becomes unmanageable – in 13 years she will have a driver’s license and then all bets will be off. 7 – 10 days in the future is outside all but the broadest weather forecast windows.

So forecasters express forecasts in terms of likelihood.  That is, there is an X% chance of such and such happening, based on history and current trends.  Sometimes it is benign.  If there is a 40% chance of showers this afternoon, you might want to bring an umbrella.  If that chance is 60% you probably should bring an umbrella.  Those two examples mean that on four out of ten days it will rain, and on six out of ten it will rain.  The official forecast language would be showers are “possible” and showers are “likely.”

So what about watches and warnings?  They are part of a larger vocabulary that includes ‘outlooks’ and ‘advisories’ and are specific levels of possibility for severe weather, weather that could have significant destructive or disruptive effect.  Thunderstorms may freak out your dog, but with normal prudence (go inside, don’t shelter under a tree or lick a flagpole) they are unlikely to cause you harm.  Severe Thunderstorms are likely to have damaging winds, torrential flooding rain, or hail of significant size.  They are also the source of tornadoes, which just for the record occur about twice every 3-4 years on average in New Jersey. 

Other types of weather that get advisories, watches, and warnings around here are snowstorms, fog, and hurricanes & tropical storms. 

The Hazardous Weather Outlook is issued a day or two in advance and does not trigger alarms on your phone.  It does appear, usually as a clickable icon, on most reputable weather apps, as do all the other notices.  The official definition is: An outlook is used to indicate that a hazardous weather or hydrologic event2 may develop. It is intended to provide information to those who need considerable lead time to prepare for the event. 

The next level is an Advisory.  Per the NWS, an Advisory highlights special weather conditions that are less serious than a warning. They are for events that may cause significant inconvenience, and if caution is not exercised, it could lead to situations that may threaten life and/or property.  So an inch of snow gets an advisory because it could make roads slick.

When things are getting serious, it is time for a Watch.  A watch is usually issued much closer to the weather event than an outlook.  The NWS says 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 probability of occurring. This is the one that will set off your phone alarm or your alert radio.  A warning is used for conditions posing a threat to life or property.  Warnings tend to be issued close to the event, while at the same time taking into account the amount of time needed for an appropriate reaction by the public.

The criteria for issuing watches and warnings is actually quite specific.  The NWS does not fly by the seat of their pants with these things.  I will put the more detailed definitions in the comments.

~~~~~~~~~~~~~~~~~

1The National Weather Service is part of a larger scientific agency called the National Oceanic and Atmospheric Administration.  In this post and others, when I refer to the NWS, I may also be referring to other departments within NOAA.  For clarity’s sake, I lump them all under NWS.

2Hydrologic Event.  Hydrology is defined as the scientific study of the waters of the earth, especially with relation to the effects of precipitation and evaporation upon the occurrence and character of water on or below the land surface.  When the NWS uses it, they generally mean flooding.

 


max_weisenfeld

Severe Thunderstorm Watch

A Severe Thunderstorm Watch is issued when severe thunderstorms are possible in and near the watch area. It does not mean that they will occur. It only means they are possible.

Severe thunderstorms are defined as follows: 1) Winds of 58 mph or higher AND/OR 2) Hail 1 inch in diameter or larger.

Severe Thunderstorm Warning

A Severe Thunderstorm Warning is issued when severe thunderstorms are occurring or imminent in the warning area.

Severe thunderstorms are defined as follows: 1) Winds of 58 mph or higher AND/OR 2) Hail 1 inch in diameter or larger.

Tornado Watch

A Tornado Watch is issued when severe thunderstorms and tornadoes are possible in and near the watch area. It does not mean that they will occur. It only means they are possible.

Tornado Warning

A Tornado Warning is issued when a tornado is imminent. When a tornado warning is issued, seek safe shelter immediately.

Tropical Storm Watch

A Tropical Storm Watch is issued when a tropical cyclone containing winds of 34 to 63 kt (39 to 73 mph) or higher poses a possible threat, generally within 48 hours. These winds may be accompanied by storm surge, coastal flooding, and/or river flooding. The watch does not mean that tropical storm conditions will occur. It only means that these conditions are possible.

Tropical Storm Warning

A Tropical Storm Warning is issued when sustained winds of 34 to 63 kt (39 to 73 mph) or higher associated with a tropical cyclone are expected in 36 hours or less. These winds may be accompanied by storm surge, coastal flooding, and/or river flooding.


marylago
max_weisenfeld said:

So forecasters express forecasts in terms of likelihood.  That is, there is an X% chance of such and such happening, based on history and current trends.  Sometimes it is benign.  If there is a 40% chance of showers this afternoon, you might want to bring an umbrella.  If that chance is 60% you probably should bring an umbrella.  Those two examples mean that on four out of ten days it will rain, and on six out of ten it will rain.  The official forecast language would be showers are “possible” and showers are “likely.”

 

 I did a survey for the NWS a number of years ago asking what I thought certain percentages of precipitation meant. It was interesting. To me, 50% means 90%, and 60% means 100%...


HatsOff

Max, this is helpful. As one of the people raising concerns on the other thread (and still sort of mulling over that conversation), would you be so kind as to help sort out some questions that I still have? 

I get the difference between outlooks, advisories, watches, and warnings. 

My biggest question concerns the very alarming phone warnings. Both WxNut and Sbenois, who I know have expertise in tornadoes, said that it was no big deal if many members of our community do not get those warnings as serious tornadoes do not happen here.

So why do we get them? I really can't parse the difference between what they said (don't worry if you didn't get it, nothing serious will ever happen here) and your strong admonition not to disable the warnings. I can't see how both of these things can simultaneously be true.

I also don't know how this works for non-tornado "serious" events. You'd need to be hiding under a rock not to know if something like Sandy was coming - that's the only life-threatening event we've had in the time I've lived in NJ. So again, I keep cycling back to why have the phone warnings at all. 



max_weisenfeld

As I said above, the warnings, with their various forms of sirens and alerts (and I mean "warning" literally) are for weather events (and civil events as well) that are, by definition, conditions posing a threat to life or property.  They are issued when those situations are occurring, are imminent, or have a very high probability of occurring.  They require prompt or immediate action.  The fact that a tornado is occurring in New Jersey and not Arkansas does not change the criteria.

I do not know how I can be more clear than posing a threat to life or property.  I don't know how they can be more timely than occurring, is imminent, or has a very high probability of occurring.  

People died during Sandy, people die every year in blizzards and hurricanes, so my take-away is that the system is necessary.  What you choose to do with the information is your concern.  If you do not find the phone alerts to be useful to you, shut them off. 


HatsOff
max_weisenfeld said:
As I said above, the warnings, with their various forms of sirens and alerts (and I mean "warning" literally) are for weather events (and civil events as well) that are, by definition, conditions posing a threat to life or property.  They are issued when those situations are occurring, are imminent, or have a very high probability of occurring.  They require prompt or immediate action.  The fact that a tornado is occurring in New Jersey and not Arkansas does not change the criteria.
I do not know how I can be more clear than posing a threat to life or property.  I don't know how they can be more timely than occurring, is imminent, or has a very high probability of occurring.  
People died during Sandy, people die every year in blizzards and hurricanes, so my take-away is that the system is necessary.  What you choose to do with the information is your concern.  If you do not find the phone alerts to be useful to you, shut them off. 


Thank you.

I take it from this then that WxNut and Sbenois were wrong that we shouldn't worry if members of our community without cell phones don't get alerts then.

This is really the crux of my concern - they kept saying it's no big deal if not everybody gets them, which says to me "they're not that important." I was genuinely confused by the contradiction, and honestly still am to a certain degree.

You and the NWS say the alerts are important. If that is the case, we need a better way to make sure that all members of our community get them. Especially since those without cell phones are likely to be more vulnerable in a number of ways.


Morganna

Loved the Matters Magazine article about you!


sac
HatsOff said:
Thank you.
I take it from this then that WxNut and Sbenois were wrong that we shouldn't worry if members of our community without cell phones don't get alerts then.
This is really the crux of my concern - they kept saying it's no big deal if not everybody gets them, which says to me "they're not that important." I was genuinely confused by the contradiction, and honestly still am to a certain degree.
You and the NWS say the alerts are important. If that is the case, we need a better way to make sure that all members of our community get them. Especially since those without cell phones are likely to be more vulnerable in a number of ways.

Just as savvy marketing/PR people know, the more urgent/important it is to get a message out, the more different ways the information should be communicated. The cell phone alerts reach a large number of people, but not everyone.  Other methods can and should be used for dangers like tornados - TV/Radio (Emergence Alert System), Robocalls and sirens are some examples. I know there have (very occasionally) been times when authorities drove around communities with bullhorns (such as during power failures that disabled some of the other methods.) And this is not an exhaustive list.


WxNut2.0
HatsOff said:


max_weisenfeld said:
As I said above, the warnings, with their various forms of sirens and alerts (and I mean "warning" literally) are for weather events (and civil events as well) that are, by definition, conditions posing a threat to life or property.  They are issued when those situations are occurring, are imminent, or have a very high probability of occurring.  They require prompt or immediate action.  The fact that a tornado is occurring in New Jersey and not Arkansas does not change the criteria.
I do not know how I can be more clear than posing a threat to life or property.  I don't know how they can be more timely than occurring, is imminent, or has a very high probability of occurring.  
People died during Sandy, people die every year in blizzards and hurricanes, so my take-away is that the system is necessary.  What you choose to do with the information is your concern.  If you do not find the phone alerts to be useful to you, shut them off. 
Thank you.
I take it from this then that WxNut and Sbenois were wrong that we shouldn't worry if members of our community without cell phones don't get alerts then.
This is really the crux of my concern - they kept saying it's no big deal if not everybody gets them, which says to me "they're not that important." I was genuinely confused by the contradiction, and honestly still am to a certain degree.
You and the NWS say the alerts are important. If that is the case, we need a better way to make sure that all members of our community get them. Especially since those without cell phones are likely to be more vulnerable in a number of ways.

 Had a whole response to this typed up that I somehow lost. To paraphrase: I never said the alerts weren't important, just that 1) there was not a substantial threat to Maplewood; 2) sounding tornado sirens in a town that doesn't know what they're for would cause hysteria; and 3) installing tornado sirens in a town that gets maybe one tornado warning a year is a waste of money. Never said that getting alerts on your phone was a bad idea. But the very same hysteria that lead to people becoming distraught over a storm that probably doesn't garner a warning in the plains states (same criteria or not, that storm doesn't get warned in Kansas) would cause all kinds of craziness if a loud horn started sounding at 9 at night and nobody knew what for. I guarantee you more people venture outside to figure out whats going on if that horn starts going. I've seen it a million times in tornado alley. 




In order to add a comment – you must Join this community – Click here to do so.