Cold Front
A cold front is the boundary where a cooler, denser air mass is advancing and replacing warmer air. The cold air wedges under the warm air and forces it upward, which often produces a band of showers or thunderstorms, followed by a wind shift and cooler, drier air.
Why It Matters
A front is a boundary between two air masses of different density, usually with different temperatures, and a moving front is named for the air mass that is advancing. Fronts are where much of the day-to-day change in the weather happens: wind shifts, temperature swings, and bands of rain or snow.
The Four Types of Front
| Front | What is happening |
|---|---|
| Cold front | Cooler, denser air is advancing and replacing warmer air |
| Warm front | Warmer air is advancing and replacing the cooler air ahead of it |
| Stationary front | The boundary between warm and cold air is moving very slowly or not at all |
| Occluded front | A cold front has caught up with a warm front or stationary front, forming a combined front |
Frequently Asked Questions
What is the difference between a cold front and a warm front?
Which air mass is advancing. At a cold front, cooler and denser air is moving in and replacing warmer air. At a warm front, warmer air is moving in and replacing the cooler air ahead of it.
What is a stationary front?
A boundary between warm and cold air that is barely moving. Neither air mass is advancing, so the weather along it can persist in the same place for a long time.
What is a dry line?
A narrow zone with a sharp contrast in moisture but little difference in temperature, separating moist air from dry air. It is also called a dew point front, and it can be a focus for severe thunderstorms.
Related Terms
Squall Line
A squall line is a line of active thunderstorms, either continuous or with breaks, together with the rain areas the storms produce. Squall lines can extend for hundreds of miles and last for many hours. Their main hazard is straight-line wind damage, though tornadoes sometimes form along the leading edge.
Shelf Cloud
A shelf cloud is a low, horizontal, wedge-shaped cloud attached to the base of a thunderstorm along its gust front, the leading edge of the storm's rain-cooled outflow. Rising cloud motion is often visible on its leading edge, while the underside looks turbulent and wind-torn. It means gusty winds are about to arrive.
Jet Stream
A jet stream is a relatively narrow band of strong wind in the upper atmosphere, typically around 30,000 feet, that blows from west to east. The polar jet sits between 50° and 60° latitude and the subtropical jet near 30°. Jet streams follow the boundaries between cold and warm air and steer the storm systems below them.
Barometric Pressure
The weight of the atmosphere pressing down on a given point, measured in inches of mercury (inHg) or millibars (mb). Rising pressure typically indicates improving weather, while falling pressure suggests approaching storms or precipitation.
Alberta Clipper
A fast-moving low-pressure system that originates near Alberta, Canada, and tracks southeast across the northern United States. Clippers typically bring light snow (1-4 inches) followed by bitter cold and gusty winds.
Snow Squall
An intense, short-lived burst of heavy snow accompanied by strong winds and often causing a sudden drop in visibility to near zero. Snow squalls can create extremely dangerous driving conditions despite lasting only 30-60 minutes.
Cold Front: Guides and Explainers
These explainers connect this definition to real-world forecasting and decision-making.
Weather Education
What Is a Derecho? The Inland Hurricane Explained
Learn what a derecho is, how it differs from tornadoes and hurricanes, why these long-lived windstorms are so destructive, and how to stay safe when one approaches.
Weather Education
What Causes Thunder and Lightning? The Science Behind Thunderstorms
Learn how lightning forms through charge separation in thunderstorm clouds, the different types of lightning, what causes thunder, and how to stay safe during electrical storms.
Weather Education
Winter Storm Watch vs Warning vs Winter Weather Advisory (Plus Blizzard, Ice Storm, and Snow Squall Warnings)
What a Winter Storm Watch, Winter Storm Warning, and Winter Weather Advisory mean, how many inches of snow trigger a warning where you live, and how Blizzard, Ice Storm, Snow Squall, and Extreme Cold Warnings differ.
Helpful Tools and Hubs
Use these pages to apply the concept, compare conditions, or follow related weather workflows.
Tool
Pressure Tendency Calculator
Calculate 3-hour barometric pressure tendency from rising or falling readings.
Tool
Wind Chill Calculator
Estimate cold-weather exposure risk from temperature and wind speed.
Guide
Lightning Safety Guide
Know when lightning becomes dangerous, how far away it can strike, and when to move indoors.
Seasonal Hub
Winter Weather Guide
Find practical explainers on snow, freezing rain, wind chill, and winter travel risk.
Sources
Explore Other Terms
GFS
Global Forecast System, the primary American global weather model run by NOAA. The GFS provides forecasts out to 16 days and is widely used for medium-range forecasting. It runs four times daily with global coverage.
IFR
Instrument Flight Rules govern flights conducted under instrument procedures and can be used in clear weather too. Separately, the IFR weather category means a ceiling from 500 to less than 1,000 feet and/or visibility from 1 to less than 3 statute miles, with lower values classified as LIFR. Legal operating requirements depend on airspace, regulations, equipment, and pilot qualifications.
Invest
A weather system designated for investigation by the National Hurricane Center. An Invest designation triggers enhanced data collection and model runs but does not indicate expected development. Many Invests never become tropical cyclones.
Blizzard
A blizzard is a storm with sustained winds or frequent gusts of 35 mph or more and falling or blowing snow that frequently reduces visibility to below a quarter mile, lasting 3 hours or longer. The National Weather Service definition has no snowfall or temperature requirement: wind and visibility make a blizzard.
Small Craft Advisory
A Small Craft Advisory is a National Weather Service alert for winds or seas that are hazardous to small boats in coastal and Great Lakes waters. The wind and sea thresholds are set separately for each geographic area. There is no precise definition of a small craft: any vessel that the conditions could affect counts.
Red Flag Warning
A Red Flag Warning is a National Weather Service alert that weather conditions could cause extreme fire behavior. It is issued when those conditions are occurring or expected within 24 hours. Typical criteria combine dry fuels with sustained winds of 15 mph or more and relative humidity of 25% or less, and exact thresholds vary by state and local office.
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