January 8, 2019, Revised September 24, 2021
© 2022 randomramblingsnj
I got the idea for writing this article on advisories, watches, and warnings issued by the National Weather Service with a special focus on Fire Weather Watches and Red Flag Warnings late last summer. At the time I was thinking about how to explain Fire Weather Watches and Red Flag Warnings to some friends of mine. I wanted to explain these concepts in non-technical terms for the general public across the entire United States. What started as a page devoted only to Fire Weather Watches and Red Flag Warnings has expanded to include other advisories, watches and warnings issued by the National Weather Service with some pertinent examples.
This article is divided into three sections. Section 1 is an introduction where I define advisories, watches, and warnings issued by the National Weather Service. Unless I mention otherwise, all references to advisories, watches, and warnings are to those issued by the National Weather Service. The focus of section 2 is fire weather including but not limited to Fire Weather Watches and Red Flag Warnings issued by the National Weather Service (NWS). Finally, in section 3, I offer examples of some weather related hazards along with any relevant advisories, watches, and warnings. Specifically, I will discuss flash floods, thunderstorms, lightning, and damaging winds.
I. Introduction: About Advisories, Watches and Warnings
Advisories, Watches, and Warnings
I start with some definitions of advisories, watches, and warnings. A simple way to think of these are:
Advisory: be aware.
Watch: be prepared.
Warning: take action.
A longer definition of each is given in the National Weather Service Glossary:
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.
Watch: 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.
Warning: A warning is issued when a hazardous weather or hydrologic event is occurring, is imminent, or has a very high probability of occurring. A warning is used for conditions posing a threat to life or property.
With the possible exception of Severe Thunder Storm Warnings, NWS products are not a one size fits all proposition. Winter Storm Warnings are one example. A forecast of a two inch snow in Atlanta, Georgia will necessitate a Winter Storm Warning. However a NWS meteorologist in northern New England will not issue a Winter Storm Warning for a forecast of a two inch snowfall. The differences in snowfall criteria across and even within the area served by one NWS weather forecast office is at least partially based on differing regional climatologies varying by elevation and even within a state. For example, within my own state of New Jersey, the forecasted 12 hour snow fall criteria for a Winter Storm Warning is six inches in northern New Jersey and five inches in southern New Jersey. This is because heavier snow is relatively more common in northern New Jersey than in southern New Jersey. Moving even further south to the southern area of the eastern shore of Maryland (Ocean City area), this region often sees even lighter snowfall accumulations, so a Winter Weather Warning kicks in for a forecast of a four inch snowfall.
How to get warnings
The National Weather Service issues Wireless Emergency Alerts (WEA) for dangerous weather conditions through mobile phone carriers to WEA enabled devices. Most smart phones are WEA enabled, older cell phones are not. Included among the Wireless Emergency Alerts issued by the NWS are: Hurricane Warnings, Typhoon Warnings, Tornado Warnings, Life-threatening Flash Flood Warnings, and Destructive Thunderstorms. You may read more about Wireless Emergency Alerts here.
Most media outlets will include NWS watches and warnings in their weather reporting. In addition, a special type of radio is available that broadcasts weather forecasts and watches and warnings issued by your local weather forecast office. You may read more about weather radios at this NWS website. Of course, you may go to the NWS webpage. Type in your town or zip code to find your local NWS weather forecast office.
II. Fire Weather: Fire Weather Watches, Red Flag Warnings and Related Advisories and Warnings
Fire Weather Watches and Red Flag Warnings
In their wildfire safety page the NWS defines Fire Weather Watches and Red Flag Warnings. More on wildfire safety may be found here.
Fire Weather Watch (Be Prepared): A Watch alerts land managers and the public that upcoming weather conditions could result in extensive wildland fire occurrence or extreme fire behavior. A watch means critical fire weather conditions are possible but not imminent or occurring.
Red Flag Warning (Take Action): Be extremely careful with open flames. The NWS issues a Red Flag Warning, in conjunction with land management agencies, to alert land managers to an ongoing or imminent critical fire weather pattern. The NWS issues a Red Flag Warning when fire conditions are ongoing or expected to occur shortly.
A Fire Weather Watch will be issued by your local weather forecast office when critical fire weather conditions may happen in the next 12 to 96 hours. The exact time frame will vary by local weather forecast office. To meet Red Flag Warning criteria, three criteria have to be met: low relative humidity (varies by region), moderate to high wind speeds, and low fuel moisture. Your weather forecast office will forecast relative humidity and wind speeds. Fuel moisture will probably come from their forestry partners. If all three criteria for your local area are met, your weather forecast office will issue a Red Flag Warning (take action) for extreme fire weather conditions that are forecast within the next 12 to 24 hours or less. The wind speeds, humidity levels and fuel dryness used in determining a Red Flag Warning will vary from weather forecast office to weather forecast office.
The specific definitions used by a weather forecast office in determining RFW will vary depending on local conditions. There are times when all three criteria for RFW may not be met, but two of three or perhaps only one of three criteria (low-end fire danger) will be met. Many but not all weather forecast offices will issue a statement when there is low-end fire danger, some weather forecast office‘s will issue a Fire Danger Statement (exact wording may vary by weather forecast office). If your weather forecast office does not issue a Fire Danger Statement, they may issue a Special Weather Statement for low-end fire danger.
In western regions of the continental United States, dry thunderstorms, specifically the lightning they produce, whether or not accompanied by moderate or high winds can cause a wildfire; especially when conditions have been dry leading up to the dry thunderstorm. A thunderstorm is considered a dry thunderstorm when rainfall is less than or equal to one-tenth of an inch. Lightning produced by a dry thunderstorm is often referred to as dry lightning.
One of the criteria used to determine Fire Weather Watches and Red Flag Warnings is wind speed. The wind speed criteria will vary across weather forecast offices and sometimes within a weather forecast office. When the winds speeds are forecast to meet the criteria for the weather forecast office to issue a High Wind Warning (see next section) they will issue a High Wind Warning
While the wildfire is going on
Fires of any kind will generate smoke, and wildfires are no exception. The concern here is that smoke is hazardous to public health. Air Quality Alerts are issued by the Environmental Protection Agency as well as State and local environmental agencies when air is forecast to be at a level to be harmful to public health. The issuing agency(ies) then forwards the Air Quality Alert (AQA) to the affected weather forecast offices who then transmit the AQA.The poor air quality could be from various air borne pollutants or smoke from a wildfire. You do not have to living in close proximity to a wildfire to be impacted from smoke. If a wildfire is causing smoke that is harmful to public health then your local weather forecast office will transmit an Air Quality Alert.
There is a direct correlation between wildfires and winds. Gusty and erratic winds can occur outside of a rain band produced by a thunderstorm (see next section for more on thunderstorms). The passage of a thunderstorm can be a big concern for those living near or fighting a wildfire as changes in wind direction can pose risks to persons and structures near the fire. Residents and firefighters who think they are safe may no longer be safe if the wind direction changes. Furthermore, changes in wind direction and wind speed can jeopardize wildland firefighters in the air as well as those on the ground. Your weather forecast office will issue Thunderstorm Warnings or High Wind Warnings as appropriate, including but not limited to while wildfires are going on in their forecast area.
In addition to their usual products, the National Weather Service often provides specific weather forecasts to wildland firefighters. These forecasts are often done behind the scenes. Spot forecasts are requested by wildland firefighter commanders in the field for the specific area where their wildfire is burning. In addition, incident commanders on many major wildfires may request specially trained Incident Meteorologists (IMETs) from the NWS. IMETs are specially trained NWS Meteorologists providing weather forecasts for a wildfire, and other natural disasters. They are deployed to an incident for up to two weeks with all the equipment that they will need to provide specific weather forecasts for the area burned by the wildfire.
After the wildfire is put out
Debris flows and flash flooding are the main concern. Mountainous areas with steep terrain that are in or near recent wildfire burn scars that experience heavy rains could generate debris flows and/or flash flooding. Rainfall rate is important here, not the amount of rainfall. If you live near such a burn scar and rain is in the forecast, check with your local weather forecast office for Flash Flood and/or Debris Flow Advisories, Watches, and Warnings.
III. Examples of Advisories, Watches Warnings, and Other Hazards
The National Weather Service has a safety webpage with links for all weather related hazards including but not limited to weather forecast office issued advisories, watches, and warnings (aka products). Links are also included for hazards, e.g. air quality alerts, that are issued by other agencies and transmitted by weather forecast offices. In this section I am going to talk about four hazards: flash flooding, thunderstorms, lightning and high winds.
Flash Flooding
The NWS flood safety page discusses flood hazards and relevant advisories, watches, and warnings in some detail including flash floods. I will leave it to you to read about Flood Watches (be prepared) and Flood Warnings (take action). There are a variety of flood products that your weather forecast office will issue based on locally determined criteria appropriate for the type(s) of flood that may occur in their forecast area. There is some variation in flooding hazards by state. To learn more about flooding hazards specific to your state go to this interactive map. You may want to familiarize yourself with what to do before, during, and after a flood. If you live near coastal waters then you will want to pay attention to any coastal flood products issued by your weather forecast office.
In any kind of flooding, if you are driving and the road ahead is flooded, the important thing is to turn around, don’t drown.
To elaborate on flash flooding and debris flows, Flash Flood Warnings are one of the Warnings that Wireless Emergency Alert (WEA) enabled smart phones will receive. Starting in November 2019, the National Weather Service changed Flash Flood Warnings to an impact-based format, all NWS Weather Forecast Offices now do impact-based Flash Flood Warnings. With this change only Flash Flood Warnings tagged as “considerable’ or “catastrophic" will be warned on WEA enabled devices, see this fact sheet for more information on this change. Flash flooding and debris flows on or near steep slopes, with or without a burn scar, can be very violent. Those of us who live in flatter terrain are not off the hook. Flash floods may not be as violent on flatter terrain as on steep slopes, but flash floods can and do occur everywhere. They can cause property damage and they do kill.
Flash Flood Warning (Take Action): A Flash Flood Warning is issued when a flash flood is imminent or occurring. If you are in a flood prone area move immediately to high ground. A flash flood is a sudden violent flood that can take from minutes to hours to develop. It is even possible to experience a flash flood in areas not immediately receiving rain.
As mentioned above, flash floods can occur in a matter of minutes. The flash flooding could be from heavy rains, with or without the complication of recent wildfire burn scars. In the case of a forecast for heavy and or prolonged rains your weather forecast office may, for example, start out with a Flood Watch or even a Flood Warning before issuing a Flash Flood Warning. If you are warned about an imminent flash flood, even if it is not raining and/or you don’t live in close proximity to a water way, it is vital that you heed warnings. Obey any evacuation warnings.
In the case of moderate or heavy rains forecast to occur in mountainous terrain with steep slopes on or near a burn scar within 24 to 72 hours, your local weather forecast office will issue an advisory or watch by means of the appropriate product for their region. Within this 24 to 72 hour window, affected residents will want to make any preparations, including getting their emergency kit ready and preparing an evacuation plan. When forecasted moderate or heavy rains in a steep mountainous area near a burn scar are imminent, your weather forecast office will issue either a Flash Flood Warning that includes wording about a debris flow or a separate Debris Flow Warning. This warning will list residential and commercial locations that may be in or near the path of debris flows or flash flooding.
Thunderstorms
Any thunderstorm can produce lightning and rain. Starting August 2, 2021 the NWS classifies severe thunderstorms by “damage threat categories”: destructive, considerable, and baseline. Destructive threat thunderstorms are capable of producing hail of least 2.75 inch hail (baseball) and/or 80 mph wind gusts, and are WEA warned; considerable threat thunderstorms are capable of producing hail of least 1.75 inch (golf ball) and/or 70 mph wind gusts. A thunderstorm falls into the baseline threat category with a threat of having wind gusts of at least 58 mph and/or producing hail of at least one inch in diameter (about the size of a quarter). When the NWS Forecaster writes a Severe Thunderstorm Warning they will will put in tags based on the appropriate damage threat category so the relevant warning is generated. It is important to remember that any thunderstorm may produce a tornado with little or no warning. You may read more about the new threat classification of severe thunderstorms here. Staying safe during severe thunderstorms is crucial, for more information please read about Severe Thunderstorm Safety.
Here is the difference between Severe Thunderstorm Watches and Warnings as defined by the NWS. When a thunderstorm is forecast that does not meet the criteria for a severe thunderstorm, your local weather forecast office will mention it in their Hazardous Weather Outlook. However, some weather forecast offices will issue Significant Weather Advisories when individual thunderstorms are approaching severe criteria.
Severe Thunderstorm Watch (Be Prepared): Severe thunderstorms are possible in and near the watch area. Stay informed and be ready to act if a severe thunderstorm warning is issued. The watch area is typically large, covering numerous counties or even states.
Severe Thunderstorm Warning (Take Action): Severe weather has been reported by spotters or indicated by radar. Warnings indicate imminent danger to life and property. Take shelter in a substantial building. Get out of mobile homes that can blow over in high winds. Warnings typically encompass a much smaller area (around the size of a city or small county) that may be impacted by large hail or damaging winds identified by a NWS forecaster on radar or by a trained spotter/law enforcement who is watching the storm.
Any thunderstorm including a thunderstorm that does not meet severe criteria often produces lightning. Any lightning is dangerous. When thunder roars go indoors!
Lightning
The NWS does not issue advisories or warnings about lightning. Even so, you still need to be aware about lightning safety because of the danger posed by lightning. See this lightning safety brochure for some important facts and tips on how to stay safe. The most important thing to know about lightning is that if you hear thunder, you are close enough to the storm to be struck by lightning. When thunder roars go indoors. Stay In your house or your car for 30 minutes after the storm passes. Check out the weather forecast early in the day for any possible forecast of thunderstorms. If thunderstorms are forecast and you are planning an outdoor activity, you should cancel your outdoor plans.
Damaging Winds
Damaging winds can occur from several meteorological phenomena including thunderstorms or derechos, coastal and frontal, mountain and valley, and dust storms and haboobs. These links have good information about these different types of winds. I will leave it to you to read what interests you, especially those that you might find where you live. Information about various wind advisories, watches and warnings issued by the NWS may be found here.
Wind Advisory (Take Action): Strong winds are occurring but are not so strong as to warrant a High Wind Warning. Objects that are outdoors should be secured and caution should be taken if driving. NWS offices issue Wind Advisories based on local criteria.
High Wind Watch (Be Prepared): Sustained, strong winds are possible. Secure loose outdoor items and adjust plans as necessary so you're not caught outside. NWS offices issue High Wind Watches based on local criteria.
High Wind Warning (Take Action): Sustained, strong winds with even stronger gusts are happening. Seek shelter. If you are driving, keep both hands on the wheels and slow down. NWS offices issue High Wind Warnings based on local criteria.
Many, but not all weather forecast offices use the same criteria for high wind warnings, 40 mph sustained winds for at least one hour or gusts of at least 58 mph. Wind patterns in mountainous areas of higher elevations will often see stronger winds than areas at lower elevations or on the side of mountains less prone to higher wind speeds. Therefore, a weather forecast office in an area that includes mountainous areas is likely to have higher high wind warning criteria for their mountains. In mountainous areas the criteria may or may not be elevation dependent depending on local geography.
Acknowledgements
I want to thank all the wonderful NWS Meteorologists from a few National Weather Service Weather Forecast Offices who answered my questions and steered me in the right direction. This article is possible because of the time many National Weather Service Meteorologists spent with me. I talked, corresponded with, or chatted on social media with several meteorologists from my local Weather Forecast Office, NWS Mt. Holly, NJ. They were very generous with their time, providing invaluable help. Meteorologists from the following National Weather Service Weather Forecast Offices helped me, providing valuable insights and answering my questions: Norman OK, Great Falls MT, Los Angeles CA, San Diego CA, Pueblo CO and Guam. Thanks to my friend, a retired NWS meteorologist, who took time to answer my questions, providing important guidance.
© 2022 randomramblingsnj
