Glossary of Weather Terms – Beginning with “B”

Looking for the full Beaufort Wind Scale, how weather balloons work, what a Blizzard Warning means, or what a bow echo on radar indicates?

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Weather Terms Beginning with “B”

Barograph

A barograph is a meteorological instrument that continuously records atmospheric pressure over time on a paper chart wrapped around a rotating drum, producing a visual graph called a barogram. Unlike a standard barometer which gives only the current pressure reading, a barograph shows trends, whether pressure is rising, falling, or steady, which is more useful for forecasting. A rapidly falling barograph trace (falling more than 0.06 inches of mercury in 3 hours) is a strong indicator of an approaching storm system.

Barometer

A barometer is the instrument used to measure atmospheric pressure. The original mercury barometer, invented by Evangelista Torricelli in 1643, uses a column of mercury to balance the weight of the atmosphere, standard sea-level pressure supports a mercury column 29.92 inches (760 mm) tall. Modern aneroid barometers use a sealed, flexible metal chamber that expands and contracts with changing pressure. Falling pressure typically signals approaching storms or precipitation; rising pressure indicates improving conditions. Pressure is reported in inches of mercury (inHg), millibars (mb), or hectopascals (hPa).

Beaufort Wind Scale

The Beaufort Wind Scale is a standardized empirical scale developed by British Admiral Sir Francis Beaufort in 1805 that relates wind speed to observed conditions at sea and on land. It runs from Force 0 (calm) to Force 12 (hurricane force) and is still widely used in marine forecasting today.

See also: Full Beaufort Wind Scale reference

Blizzard

A blizzard is a severe winter storm with three specific criteria that must all be met simultaneously: sustained winds or frequent gusts of 35 mph or greater, falling or blowing snow that reduces visibility to 1/4 mile or less, and these conditions must persist for at least 3 consecutive hours. A blizzard does not necessarily require heavy snowfall, in fact, a “ground blizzard” can occur with no new snow if strong winds pick up previously fallen dry snow. The combination of wind and reduced visibility, not snowfall amount, is what defines a blizzard and makes it life-threatening.

Blizzard Warning

A Blizzard Warning is issued by the National Weather Service when blizzard conditions, sustained or frequent winds of 35 mph or greater with snow reducing visibility to 1/4 mile or less for 3 or more hours, are imminent or occurring. During a Blizzard Warning, travel is strongly discouraged and may become impossible. If you must travel, carry a winter survival kit including blankets, water, food, a flashlight, and a phone charger. Exposure to blizzard conditions on foot can lead to hypothermia within minutes.

Blizzard Watch

A Blizzard Watch is issued when conditions are favorable for blizzard conditions within 24 to 48 hours. A Watch means blizzard conditions are possible but not yet certain, it is the time to stock up on supplies, fuel your vehicle, charge electronics, and make a plan for staying home or sheltering in place if the storm materializes. Blizzard Watches are often issued 12-36 hours before a major winter storm to give residents maximum preparation time.

Blizzard Warning vs. Winter Storm Warning, Key Differences

Blue Norther

A Blue Norther is a colloquial term for an intense, fast-moving cold front that sweeps across Texas and the southern Great Plains, producing a dramatic and sudden drop in temperature, sometimes 50°F or more within a few hours. The name refers to the dark blue-black appearance of the sky behind the advancing cold air. Blue Northers can drop temperatures from the 70s to below freezing in a single afternoon, catching residents unprepared. They are most common from October through March.

Bow Echo

A bow echo is a radar signature in which a line of thunderstorms bows outward into a distinctive arc or “bow” shape. Bow echoes form when a powerful downdraft at the center of a squall line accelerates the storm forward, bending the line. The apex of the bow is where the strongest, most damaging straight-line winds occur, gusts of 60-100 mph or more are common. A small comma-shaped feature at the northern end of the bow (called a “bookend vortex”) can also produce brief tornadoes. Bow echoes are one of the most recognizable and dangerous radar signatures.

Breeze (Land Breeze and Sea Breeze)

A sea breeze is a local wind that blows from a cooler body of water toward a warmer land surface during the daytime. As land heats up faster than water in the afternoon, air rises over land and cooler marine air flows inland to replace it. Sea breezes are responsible for the pleasant cooling along coastlines during summer afternoons and can trigger afternoon thunderstorms along Florida’s coasts where opposing sea breezes converge. A land breeze is the nighttime reversal, land cools faster than water after sunset, so the air over water becomes relatively warmer and the cool land air flows seaward.

Weather Balloon (Radiosonde)

A weather balloon carries a radiosonde, an instrument package measuring temperature, humidity, pressure, and wind speed/direction at multiple levels of the atmosphere, from the surface to approximately 100,000 feet (19 miles) before the balloon bursts. The NWS launches weather balloons twice daily at 12:00 UTC and 00:00 UTC from approximately 900 sites worldwide, including 92 in the United States. The upper-air data collected is essential for initializing computer weather forecast models, without it, forecast accuracy would drop dramatically within 12-24 hours. The balloon, typically about 6 feet in diameter at launch, expands to roughly 20 feet before bursting; the radiosonde descends on a small parachute and can sometimes be recovered.

See also: Weather Balloons, detailed overview.

Frequently Asked Questions, “B” Weather Terms

What is the difference between a Blizzard Warning and a Winter Storm Warning?

A Winter Storm Warning is issued for any combination of heavy snow, ice, or sleet that makes travel hazardous, it does not require a specific wind speed or visibility threshold. A Blizzard Warning requires all three criteria simultaneously: winds of at least 35 mph, visibility reduced to 1/4 mile or less by blowing or falling snow, and those conditions lasting 3 or more hours. A Blizzard Warning is generally more dangerous because near-zero visibility makes it possible to become disoriented and fatally exposed even a short distance from shelter.

What wind speed qualifies as a blizzard?

A blizzard requires sustained or frequently gusting winds of at least 35 mph combined with snow that reduces visibility to 1/4 mile or less for 3 or more hours. Wind speed alone does not make a blizzard, all three criteria must be met at the same time. A storm can produce 2 feet of snow without qualifying as a blizzard if winds stay below 35 mph, and conversely, a ground blizzard with no new snowfall can occur when high winds pick up dry, loose snow from the ground.

What is the Beaufort Wind Scale used for today?

The Beaufort Wind Scale remains widely used in marine and coastal forecasting to communicate wind conditions without requiring precise wind speed measurements. Sailors, fishermen, and coastal operators use Beaufort force numbers to quickly assess sea state and safe operating conditions. Forces 6 and above (25 mph+) signal rough seas; Forces 10-11 indicate storm conditions. On land, the scale is a useful reference for estimating wind speeds from observable effects, if large trees are moving, you are experiencing roughly Force 7 (32-38 mph) winds.

What is a bow echo on radar and why is it dangerous?

A bow echo is a distinctive arc-shaped radar signature indicating a line of thunderstorms with a powerful downdraft bowing the line outward. The center of the bow is where the strongest straight-line winds occur, often 60-100 mph or more. These winds are sometimes called a “derecho” when they persist across a long path. Bow echoes can produce widespread wind damage over hundreds of miles in a matter of hours, affecting areas that received no tornado warning. Any time forecasters identify a bow echo on radar, a Severe Thunderstorm Warning with a Destructive tag is likely.

What do weather balloons measure?

Weather balloons carry a radiosonde instrument package that measures temperature, humidity, and atmospheric pressure at multiple levels from the surface to about 100,000 feet. Wind speed and direction at each level are calculated from the balloon’s tracked movement. This upper-air data is launched twice daily from nearly 900 sites worldwide. The data is fed directly into computer weather forecast models and is critical for accurate forecasts, particularly for predicting the intensity and track of winter storms, severe weather outbreaks, and hurricanes.

What is a Blue Norther and where does it occur?

A Blue Norther is a rapidly advancing cold front that moves across Texas and the southern Plains, causing a sudden dramatic temperature drop, sometimes 40-50 degrees Fahrenheit in just a few hours. The term comes from the characteristic blue-black wall of clouds behind the cold air. Blue Northers are most common from October through March and can catch people off guard on days that start mild and end near freezing. They are one of the most visually dramatic weather events in Texas weather lore.

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