Severe weather terminology in the Computer Area

**Severe weather terminology in the Computer Area** is the criteria for issuing weather alerts in the Computer Area. The Computer Weather Center is the weather service responsible for issuing forecasts and weather alerts for the Computer Area.

## Weather alerts

These are weather warnings issued by the CWC.

### Severe weather

* **Severe thunderstorm watch** - Issued when conditions are favorable for the development of severe weather, specifically the following: wind gusts of at least 56 mph, hail at least 0.88 inches in diameter and rainfall exceeding 1.9 inches. Additionally, if the risk is not significant enough for tornadoes to prompt a tornado watch, a tornado risk may be mentioned in the severe thunderstorm watch.
* **Severe thunderstorm warning** - Issued when imminent or occurring severe thunderstorms are expected to or will produce the following: wind gusts of at least 56 mph, hail at least 0.88 inches in diameter and rainfall exceeding 1.9 inches. Additionally, if the risk is not significant enough for tornadoes to prompt a tornado watch, a tornado risk may be mentioned in the severe thunderstorm warning.
* **Tornado watch** - Issued when conditions are favorable for the development of tornadoes. **WILL** mention other severe weather hazards if there are any in the watch.
* **Tornado warning** - Issued when a thunderstorm that is spotted producing a tornado, or a thunderstorm that is possibly producing a tornado. **WILL** mention other severe weather hazards if there are any in the warning.

### Tropical cyclones

* **Tropical storm watch** - Issued when a tropical storm or a developing tropical storm is expected to threaten land within the next 48 hours. It is issued when sustained gales of 39 to 73 mph are possible in that specified region in 48 hours. It may also be issued if a hurricane that is expected to impact the region in 48 hours but be far enough way so that sustained gales are less than hurricane-force.
* **Tropical storm warning** - Issued when sustained gales of 39 to 73 mph are expected in the area within 36 hours due to a tropical cyclone.
* **Hurricane watch** - Issued when a hurricane or a developing hurricane could possibly bring sustained gales of at least 74 mph within 48 hours.
* **Hurricane warning** - Issued when a hurricane or a strong tropical storm that might intensify to hurricane intensity just before landfall is expected to bring sustained gales of 74 mph or greater within 36 hours.

### Winter weather

###### **Winter weather advisory** - Issued for when winter weather may pose a risk to travel and other activities.

* **Winter weather advisory for snow:** Issued when rapidly accumulating snow is expected to fall within 24 hours but not exceed 5 inches of accumulation, or a snowfall warning will be issued.
* **Winter weather advisory for freezing rain/drizzle:** Issued when rain/drizzle is expected to freeze upon contact with the surface and cause slippery roads. The accumulations must not be too high, or a winter storm or ice storm warning will be issued instead.
* **Winter weather advisory for sleet:** Issued when sleet is expected to fall and cause hazardous conditions. Accumulations must not be too high, or a winter storm or ice storm warning will be issued instead.
* **Winter weather advisory for blowing snow:** Issued when blowing snow is expected to reduce visibility down to at least 0.5 miles for at least 3 hours. Visibility must not be lower than 0.25 miles, or a blizzard warning will instead be issued.

###### **Winter storm watch** - Issued when a winter storm is expected to impact the area within 2 days. It is issued in several ways below:

* A blizzard\*.
* A significant snowfall (5 inches or more within a 24-hour period); and
* A significant snowfall (snowfall warning criteria) combined with other winter weather hazard types such as: freezing rain, strong winds, blowing and/or extreme windchill.

\*A blizzard warning is issued instead of a winter storm warning.

###### **Winter storm warning** - Issued when hazardous winter weather conditions that exceed criteria for a winter weather advisory are expected.

* A significant snowfall (5 inches or more within a 24-hour period); and
* A significant snowfall (snowfall warning criteria) combined with other winter weather hazard types such as: freezing rain, strong winds, blowing and/or extreme windchill.
* **Blizzard warning** - Issued when blizzard conditions, which are the following: winds of 25 mph or greater reducing visibility to 0.25 miles due to blowing snow or blowing snow in combination with falling snow is expected for at least 4 hours.

###### **Snow squall watch** - Issued when conditions are favorable for the development of heavy snow squalls that significantly reduce visibility, cause blowing snow and heavy snowfall and last no more than 4 hours. They are issued in two different ways below:

* **Open water** - Issued when, near a large body of water, conditions are favorable for the development of snow squalls with one or more of the following conditions:
* Locally intense snowfall resulting in accumulations of 5 inches or more in 12 hours or less.
* Reduced visibility to less than 0.25 miles, caused by heavy snow, with or without blowing snow, for 3 hours or more
* **Frontal** - Issued when conditions are favorable for the development of snow squalls that produce brief periods of heavy snow and very poor visibilities caused by heavy snowfall and blowing snow due to the passage of a cold front.

###### **Snow squall warning** - Issued when imminent or occurring snow squalls are expected to cause significantly reduced visibility, heavy snowfall and strong winds.

* **Open water** - Issued when, near a large body of water, snow squalls are imminent or occurring with at least one of the following conditions:
* Locally intense snowfall resulting in accumulations of 5 inches or more in 12 hours or less.
* Visibility reduced to 0.25 miles or less, caused by heavy snowfall, with or without blowing snow, for at least 3 hours.
* **Frontal** - Issued when a short period (less than an hour) of poor visibilities of 0.25 miles or less caused by heavy snowfall and blowing snow, accompanied by strong, high winds of 25 mph or more, is expected due to the passage of a cold front.