US National Weather Service Voyage Tips and guide

	Note: This article does not have a list of active alerts. To check if your area is under an alert, check the National Weather Service's Official Website.

The US National Weather Service (NWS) is the main source for weather forecast and weather alerts in the United States and its territories. The agency is fully owned and funded by the government in conjunction with the National Oceanic and Atmospheric Administration, which monitors the oceans and atmosphere.

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The National Weather Service has 120 offices across all 50 states, Hawaii, Alaska, Guam (also forecasts for the Northern Mariana Islands), and Puerto Rico (also forecasts for the U.S. Virgin Islands). On the right is a map of the offices in the contiguous 48 states and their zones.

This is the Enhanced Fujita Scale. This is the scale for tornadoes. This scale goes from EF0 (light) to EF5 (catastrophic).

This is the heat index chart. It's basically what it feels like outside relative to the temperature (in Fahrenheit) and the humidity percentage.

Warning criterias are from the NWS offices of Baltimore, MD/Washington DC (LWX), Caribou, ME (CAR), Wilmington, NC (ILM), and Spokane, WA (OTX).

A winter storm warning is issued when a major storm with snow, wind, or cold weather. For this warning to be issued, it must reach at least one of the following criteria:

1. 5 inches (13 cm) or more of snow/sleet within a 12-hour period or 7 inches (18 cm) or more of snow/sleet within a 24-hour period
2. Enough ice accumulation to cause damage to trees or powerlines
3. A life threatening or damaging combination of snow and/or ice accumulation with wind

A blizzard is usually defined as a storm with blowing snow and low visibility, so that is what this warning is about. For this warning to be issued, it must reach all of the following criteria:

1. Snow and/or blowing snow reducing visibility to 1/4 mile (2/5 km) or less for 3 hours or longer
2. Sustained winds of 35 mph (56 km/h) or greater or frequent gusts to 35 mph (56 km/h) or greater

Unlike most "winter weather" warnings, there is no temperature requirement that must be met to achieve blizzard conditions.

A freeze warning is issued when significant freezing temperatures are expected. For this warning to be issued, it must reach at least one of the following criteria:

1. Temperatures are projected to go below 32 °F (0 °C) for a long period of time
2. Temperatures drop below 28 °F (−2 °C) (this can kill most types of commercial plants and crops)

An extreme cold warning (previously a wind chill warning) is issued when wind chill or temperatures get extremely low compared to the normal temperature for the area.

Local NWS offices have different standards for issuing an extreme cold warning, however most issue them when the temperature goes below 20 °F (-7 °C).

A severe thunderstorm warning (severe T-storm warning) is issued when severe thunderstorms are expected in the area. For this warning to be issued, it must reach at least one of the following criteria:

1. Winds of 58 mph (93 km/h) or higher
2. Hail of 1 inch (3 cm) in diameter or larger

A PDS (Particularly Dangerous Situation) severe thunderstorm warning, also known as a destructive thunderstorm, is issued when a severe thunderstorm is capable of causing structural damage. For this warning to be issued, it must reach at least one of the following criteria:

1. Winds of 80 mph (129 km/h) or higher
2. Hail of 2 inches (5 cm) or larger

A PDS Severe Thunderstorm Warning is also issued when a severe thunderstorm is expected to impact a densely populated area. These are issued under the criteria of a normal Severe T-Storm Warning, but are issued as a PDS.

A high wind warning is issued when high winds are expected for a period of time. For this warning to be issued, it must reach at least one of the following criteria:

1. Sustained winds of over 40 mph (64 km/h) for an hour or more
2. Wind gusts of over 58 mph (93 km/h)

An extreme wind warning is when gusts capable of causing catastrophic damage occurs. An extreme wind warning is NOT associated with a tornado or hurricane. For this warning to be issued, it must reach at least one of the following criteria:

1. Surface winds of 115 mph (185 km/h) or more
2. Sustained hurricane-like winds are expected within the next hour

A tornado watch is issued when a severe thunderstorm capable of producing tornadoes is possible in the area.

Currently, the minimum tornado probabilities for a tornado watch issuance require a ~30% chance of two or more tornado reports and, for PDS watches, an 80% chance of one or more strong tornadoes within the watch area over the valid time period.

A tornado warning is issued when a tornado is imminent.

There are three types of tornado warnings:

1. Radar Indicated: A doppler radar indicated rotation of a storm, signifying a tornado.
2. Radar Confirmed: A doppler radar indicates that debris is flying in the air, meaning a tornado is there.
3. Confirmed Tornado: A storm spotter or law enforcement has confirmed a tornado is on the ground.

A PDS (Particularly Dangerous Situation) tornado warning is issued when a long-lasting tornado, a severe tornado, or a tornado who's projected path goes through densely populated areas is imminent.

A tornado emergency is issued when a life-threatening tornado capable of causing catastrophic damage is imminent. Seek shelter immediately!

A coastal flood warning is issued when the low-lying areas around a coastline are expected to be submerged by seawater. For this warning to be issued, it must reach at least one of the following criteria:

1. Significant beach erosion
2. Destructive wave action
3. Flooding of 2 feet (0.61 m) or more

A flood warning is issued when a flood is expected. This warning is issued when any of these happen:

1. Flood monitoring and prediction tools or RFC guidance indicate flooding is likely
2. When flooding is reported
3. When the area covered by an existing flood watch increases

A river flood warning is issued when a surplus of rain causes a river to overflow and flood the surrounding area. This warning is issued when any of these happen:

1. Flood monitoring and prediction tools or RFC guidance indicate a river forecast point will crest at or above flood stage
2. When flooding is reported from a river
3. When the area covered by an existing flood watch increases

A flash flood warning is issued when an influx of water causes flooding in a short period of time. This warning is issued when any of these happen:

1. Flash flooding is reported
2. Precipitation capable of causing flash flooding is indicated by radar, gage reports, or satellite
3. Local tools indicate flash flooding is likely
4. A dam failure, or failure of a naturally caused stream obstruction (debris slide, ice jam) is imminent or occurring

   

A flash flood emergency is issued when a life-threatening flash flood that can cause catastrophic damage is imminent.

A tropical storm warning is issued when sustained winds of 39-73 mph (63-117 km/h) associated with a cyclone is expected within the next 36 hours. These winds can be accompanied by storm surge or coastal/river flooding.

A hurricane warning is issued when sustained winds of 74 mph (119 km/h) or higher associated with a tropical cyclone are expected in 36 hours or less. These winds may be accompanied by storm surge or coastal/river flooding.

A storm surge warning is issued when life-threatening flooding from rising tidal water moving inland from the shoreline occurs, generally within 36 hours. This is usually accompanied by tropical cyclones.

An extreme heat warning (also known as an excessive heat warning) is issued when the heat index value is over 110 °F (43 °C). This warning may be issued for lower criteria if it is early in the season or during a multi-day heat wave.

A red flag warning is issued when conditions are favorable to start a wildfire. For this warning to be issued, it must meet at least 2 of the following criteria:

1. Relative humidity of 25% or less
2. Sustained winds of 20+ mph or gusts of 30+ mph
3. Dry lightning
4. A significant wind shift during times of active fire suppression
5. High, Very High, or Extreme fire danger, as assessed by the natural resource agencies

All marine warnings are issued only over water.

A gale warning is issued when sustained surface winds, or frequent gusts between 39 mph to 54 mph are either predicted or occurring. Gale warnings are not usually associated with a tropical cyclone.

A small craft advisory is issued when sustained winds ranging between 25 to 33 knots (29-38 mph) and/or waves of 5 to 7 feet and greater are expected or are occuring.

A hurricane force wind warning is issued when sustained winds of 64 knots (74 mph) or more that are not associated with a tropical cyclone are expected within the next 24 hours.

A storm warning is issued when sustained winds of 48-63 knots (55-72 mph) that are not associated with a tropical cyclone are expected within the next 24 hours.

A heavy freezing spray warning is issued when an accumulation of freezing water droplets at a rate of 2 cm (0.787 in) per hour or greater caused by some appropriate combination of cold water, wind, and cold air temperature occur.

A high surf advisory is issued when waves get over 7 feet (2 meters) in height or over 5 feet (1.5 meters) in height for a period of 10 seconds or longer. In some areas, high surf advisories are issued Memorial Day weekend (last Monday of May) through Columbus Day weekend (second Monday of October).

A rip current statement is issued when rip current risks are high, but do not meet the criteria of a high surf advisory. Just like a high surf advisory, rip current statements are issued Memorial Day weekend (last Monday of May) through Columbus Day weekend (second Monday of October) in some areas.

A dense smoke advisory is when smoke causes visibility to drop below 1/4 mile (2/5 km).

An air stagnation advisory is issued when atmospheric conditions are stable enough to cause air pollutants to accumulate. For this warning to be issued, it must reach all of the following criteria:

1. Morning and afternoon mixing height (where pollutants mix and disperse) of 1,500 ft above ground level or less
2. Morning and afternoon transport winds of 10 kts (12 mph) or less
3. Conditions are likely to continue for at least 72 hours
4. Air stagnation is underway or is expected to start within the next 24 hours

An air quality alert is issued when an AQI (Air Quality Index) score for an area is expected to or is over 150.

A dust storm warning is issued when a sudden drop in visibility to 1/4 mile (2/5 km) or less is caused by widespread or localized blowing dust.

An ash fall advisory is issued when an airborne ash plume resulting in ongoing deposition occurs at the surface. Ashfall may originate directly from a volcanic eruption or from the re-suspension (by wind) of a significant amount of relic ash.

	Note: During times of severe weather, always have a radio that can connect to a NWS radio station to get updates on the situation. To find your local NWS radio frequency, go to this site.

	WARNING: Do NOT take shelter under a bridge! The winds from a tornado tend to get funneled under a bridge, and flying debris that is funneled under the bridge can injure or kill.

If you are indoors, stay away from windows and go to the lowest floor. If you have one, go into the basement. If there is no basement, go to a center room with no windows, such as a closet. If in the bathroom, lie down in the tub. Crouch down and if you have some padding such as a mattress to protect you from flying or falling debris, put that over you. Do not waste time by trying to save property.

If you are in an apartment complex or something similar, never use an elevator, you'll be trapped if the electricity goes out, and there's always a chance that the lift mechanism will give out if the roof is damaged.

If you are outdoors and there is no time to get to a shelter, your best bet is to get inside a ditch, lie flat, and cover up. Get out of a mobile home if you are in one, studies have shown that a mobile home is the worst place you can be during a tornado. If you are in your automobile and you see a tornado coming, don't try to out-run it; tornadoes can easily outrun a car driving into a 100-mph headwind.

During cold weather, make sure to stay inside or near a heat source. Shut off water pipes, as they can freeze and burst. Try not to travel during this time. If you have to, make sure your car can start up in cold weather, and get some antifreeze, car chains, and a winter survival kit.

If you are a farmer, protect livestock and irrigation pipes. Use a frost cloth to put over your crops until the cold weather passes. Add extra mulch to roots, such as potatoes and carrots.

Always bring sunscreen and a lot of water if you are going outside during hot weather. Wear lightly colored clothing, as those absorb the least heat. Have a first aid kit ready just in case.

If going camping during the hot months, expect to need a gallon of water per day per person in the event that an emergency situation develops.

• Storm chasing
• Thunderstorms