Glossary of Weather Terms – Beginning with “G”

Wondering about gale warning meaning, what is graupel, how a gust front works, what geomagnetic storm effects feel like on the ground, or what is a gustnado?

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Weather Terms Beginning with “G”

Gale

A gale is a strong wind with sustained speeds of 34-47 knots (39-54 mph) on the Beaufort Wind Scale, corresponding to Force 7-9. The term originates from the age of sail and remains in common use in marine meteorology. At sea, gale-force winds can produce significant wave heights of 13-23 feet; on land, gale-force winds can uproot shallow-rooted trees, damage roofs, overturn high-profile vehicles, and make outdoor activities hazardous. Gales are common in winter storms, nor’easters, and ahead of strong cold fronts across the northern and central United States. Sustained winds of this magnitude are sufficient for the NWS to issue a High Wind Warning over land or a Gale Warning for marine areas.

Gale Warning (Marine)

A Gale Warning is a marine weather product issued by the NWS for coastal and inland waters when sustained winds of 34-47 knots (39-54 mph) are forecast. Upon issuance, mariners should seek safe harbor or remain in port; recreational boaters should not venture onto the water. A Gale Warning is distinct from a Storm Warning (48-63 knots) and a Hurricane Force Wind Warning (64+ knots), which represent progressively more dangerous conditions. Gale Watches are issued 24-48 hours before expected gale conditions to give mariners advance notice. These marine-specific products are separate from the land-based wind advisories and warnings issued for the same storm. See also: Criteria for a High Wind Warning and Criteria for a High Wind Advisory.

Geomagnetic Storm

A geomagnetic storm is a temporary, major disturbance of Earth’s magnetosphere caused by a solar wind shock wave following a solar flare or coronal mass ejection (CME) from the sun. Geomagnetic storms are rated on the Kp-index from G1 (minor) to G5 (extreme). Effects include disruption of GPS signals, HF radio communications, and satellite operations. In extreme G4-G5 events, geomagnetically induced currents can surge through power grid transformers, potentially causing widespread blackouts, the 1989 Quebec geomagnetic storm caused a 9-hour blackout affecting 6 million people. A notable side effect of geomagnetic storms is enhanced aurora (Northern/Southern Lights) visible at unusually low latitudes, sometimes as far south as Florida and Texas during G4-G5 events.

Glaze Ice

Glaze ice is a clear, smooth coating of ice formed when supercooled liquid water, rain or drizzle, freezes on contact with surfaces. It is the most hazardous form of winter precipitation because coated roads appear wet rather than icy, making it nearly invisible to drivers. This phenomenon is sometimes called black ice because the ice is transparent and the dark road surface shows through. Even 1/8 inch of glaze ice dramatically reduces friction on roads and walkways. Accumulations of 1/4 inch or more can bring down tree limbs and power lines, causing widespread outages. Glaze ice forms during freezing rain events and can also form when fog settles over surfaces that are below 32°F.

Graupel

Graupel, also called soft hail or snow pellets, forms when supercooled water droplets in a cloud freeze onto falling snowflakes through a process called riming, coating them in a layer of white, opaque ice. The result is a small, rounded, roughly spherical pellet typically 2-5mm in diameter. Graupel is softer, lower-density, and crumbles more easily than hail. It is common in winter thunderstorms and along cold fronts, often preceding heavy snowfall or a precipitation-type transition. Graupel is particularly hazardous on roads and walkways because the round pellets behave like ball bearings underfoot and under tires, reducing traction significantly even in small accumulations.

Greenhouse Effect

The greenhouse effect is the process by which certain atmospheric gases, primarily water vapor, carbon dioxide, methane, and nitrous oxide, absorb and re-emit infrared radiation emitted by Earth’s surface, warming the lower atmosphere rather than allowing the heat to escape directly to space. The natural greenhouse effect is essential for life: without it, Earth’s average surface temperature would be approximately 0°F rather than 59°F. The enhanced greenhouse effect refers to additional warming caused by human-generated increases in CO2 and other greenhouse gases from burning fossil fuels and land use changes. The global average surface temperature has increased approximately 1.1°C above pre-industrial levels, driving shifts in weather patterns, precipitation, and extreme event frequency. See also: What is the Difference Between Weather and Climate?

Ground Blizzard

A ground blizzard produces full blizzard conditions, visibility under 1/4 mile and winds at or above 35 mph, through the blowing and drifting of existing snow on the ground rather than from new snowfall. After a storm deposits loose, dry, powdery snow, a subsequent surge of strong Arctic winds can lift that snow and create complete white-out conditions under otherwise clear or partly cloudy skies. Ground blizzards are especially common on the Northern Plains following Arctic cold fronts and are responsible for numerous highway accidents when drivers encounter sudden white-out conditions on what appears to be a clear day. The NWS may issue a Blizzard Warning specifically for ground blizzard conditions even when no new snow is falling.

Wind Gust

A wind gust is a sudden, brief increase in wind speed significantly above the average (sustained) wind speed. The NWS defines a gust as a rapid fluctuation in wind speed with a variation of at least 10 knots (11.5 mph) between peaks and lulls, lasting less than 20 seconds. Peak gusts in severe thunderstorms can reach 70-100+ mph and are capable of felling trees, destroying poorly constructed structures, and sending debris airborne. Wind damage from gusts is the most common type of severe weather damage reported in the United States. High Wind Warnings and Wind Advisories are issued based on both expected sustained wind speeds and peak gust values, gusts are often 40-50% higher than the sustained wind speed.

Gust Front

A gust front is the leading edge of a pool of cold, dense air that flows outward from a thunderstorm’s downdraft along the ground, undercutting warmer surface air and forcing it rapidly upward ahead of the storm. Gust fronts are visible on Doppler radar as a thin arc of slightly enhanced radar reflectivity ahead of a thunderstorm complex. They produce the sudden shift in wind direction and speed, and the rush of cool air, that people feel just before a severe thunderstorm arrives. Gust fronts can outrun the parent storm by miles and trigger new thunderstorm development along their boundaries. The dramatic and sudden wind shift at the approach of a severe storm is the gust front arriving at the surface.

Gustnado

A gustnado is a brief, weak tornado-like vortex that forms along a thunderstorm’s gust front, spinning up from the ground surface rather than descending from the cloud base. Gustnadoes are typically short-lived (seconds to a few minutes), narrow (under 50 yards wide), and weak (usually EF0-EF1 intensity). Unlike a true tornado, a gustnado is not connected to a rotating updraft (mesocyclone) in the parent thunderstorm. Despite this distinction, gustnadoes can cause localized wind damage and are frequently mistaken for tornadoes by witnesses. The NWS does not typically issue a Tornado Warning specifically for a gustnado, though a Severe Thunderstorm Warning covering the parent storm may already be in effect.

Gulf Stream

The Gulf Stream is a powerful, warm ocean current in the Atlantic Ocean that originates in the Gulf of Mexico, flows northward along the eastern US coast, and then curves northeast across the Atlantic toward northwestern Europe. It is one of the most powerful ocean currents in the world, transporting roughly 30 million cubic meters of water per second, more than 150 times the combined flow of all the world’s rivers. The Gulf Stream profoundly influences the climate of the eastern US and northwestern Europe by transporting warm tropical water northward. The temperature contrast between warm Gulf Stream waters and the cold land surface of the eastern seaboard during winter contributes directly to the development of intense nor’easters and powerful offshore storms.

Frequently Asked Questions, “G” Weather Terms

What is the difference between a Gale Warning and a High Wind Warning?

A Gale Warning is a marine product issued by the NWS for coastal and inland waters when sustained winds of 34-47 knots (39-54 mph) are expected; it applies to boaters and mariners. A High Wind Warning is a land-based product issued when sustained winds of 40+ mph or gusts of 58+ mph are expected, impacting motorists, structures, and outdoor activities. The two systems are separate, a Gale Warning over water does not automatically mean a High Wind Warning exists for nearby land areas, and the two may be issued independently based on conditions in their respective domains.

What is graupel and is it the same as hail?

Graupel (also called soft hail or snow pellets) forms when supercooled water droplets freeze onto snowflakes, coating them in rime ice to create soft, white, rounded pellets about 2-5mm across. Hail forms through a different process, water droplets accumulate in layers as updrafts carry them repeatedly through a cumulonimbus cloud, producing dense, hard balls of ice. Graupel is soft, low-density, and crumbles easily; hail is hard and dense. Graupel is common in winter storms and along cold fronts; hail is primarily a warm-season severe thunderstorm phenomenon driven by strong updrafts.

What is a gust front and why does it matter?

A gust front is the leading edge of cold, dense air flowing outward from a thunderstorm’s downdraft along the ground. As this cold pool pushes ahead of the storm, it undercuts warm surface air and forces it rapidly upward, which is why you feel a sudden rush of cool, gusty wind right before a severe thunderstorm arrives. Gust fronts can trigger new thunderstorm development along their boundaries and sometimes produce gustnadoes, brief, weak rotating vortices. The dramatic wind shift at the leading edge of an approaching storm is the gust front arriving at your location.

What is a geomagnetic storm and can it affect daily life?

A geomagnetic storm is a disturbance in Earth’s magnetic field caused by a burst of solar wind from a solar flare or coronal mass ejection. Minor storms (G1) occur several times a year and produce enhanced auroras but rarely affect daily life. Severe storms (G4-G5) can disrupt GPS navigation, HF radio communications, airline communications over polar routes, and satellite operations. In extreme cases, geomagnetic storms can induce dangerous voltage surges in electrical grids, the 1989 Quebec storm caused a 9-hour blackout affecting millions of people. Enhanced aurora visible at unusually low latitudes is often the most widely noticed effect of a strong geomagnetic storm.

What is a ground blizzard?

A ground blizzard creates full blizzard conditions, visibility under 1/4 mile and winds over 35 mph, entirely through the blowing and drifting of snow already on the ground, with no new snowfall occurring. After a storm deposits loose, dry, powdery snow, a subsequent surge of strong Arctic winds can pick it up and create complete white-out conditions under clear skies. Ground blizzards are particularly common on the Northern Plains and are responsible for many highway accidents when drivers are caught off guard by sudden white-out conditions on what appears to be a clear day.

What is the greenhouse effect?

The greenhouse effect is the natural warming process by which atmospheric gases, primarily water vapor, carbon dioxide, and methane, absorb and re-emit infrared radiation from Earth’s surface, trapping heat in the lower atmosphere. Without the natural greenhouse effect, Earth’s average temperature would be around 0°F instead of 59°F, making the planet largely uninhabitable. The enhanced greenhouse effect occurs when human activities increase concentrations of CO2 and other greenhouse gases, amplifying this warming beyond natural levels and contributing to long-term shifts in climate, precipitation patterns, and the frequency of extreme weather events.

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