Skew-T
Also called: Skew-T Log-P diagram, sounding
A Skew-T Log-P diagram is the chart meteorologists use to plot a weather balloon sounding: temperature, dew point, and wind from the ground to the upper atmosphere. Its temperature lines are tilted 45 degrees, which gives the chart its name. A hodograph, often shown beside it, plots how wind speed and direction change with height.
Why It Matters
A sounding is the most direct look at the air above a location, and the Skew-T is how it is read. It shows where the air is moist or dry, where temperature inversions sit, how unstable the atmosphere is, and how the wind changes with height.
The National Weather Service operates 92 upper-air stations: 69 in the contiguous United States, 13 in Alaska, nine in the Pacific, and one in Puerto Rico. Most launch a balloon twice a day, at 00Z and 12Z. A flight can last more than two hours and climb above 115,000 feet.
How to Read It
- Pressure lines run horizontally, from 1050 mb at the bottom to 100 mb at the top, on a logarithmic scale. Height increases up the chart.
- Temperature lines slant up and to the right at 45 degrees.
- The two plotted traces are temperature (right) and dew point (left). Where they sit close together the air is moist, and where they spread apart it is dry.
- Dry adiabats show how unsaturated air cools as it rises, about 9.8°C per 1,000 meters. Moist adiabats show the slower cooling of saturated air, about 4°C per 1,000 meters near the surface.
- CAPE is the area between the path of a rising parcel and the temperature trace, where the parcel is warmer than its surroundings.
- Wind is plotted along the side of the chart, and on the hodograph as a curve that shows wind shear at a glance.
Related Terms
CAPE
CAPE (Convective Available Potential Energy) is the amount of energy a rising parcel of air can draw from the atmosphere, measured in joules per kilogram (J/kg). The higher the CAPE, the faster a storm's updraft can rise, and the stronger thunderstorms can become once something sets them off.
Lifted Index
A stability index comparing the temperature of a rising air parcel to the environment at 500mb (about 18,000 feet). Negative values indicate instability. Values below -6 suggest strong instability and severe thunderstorm potential.
Temperature Inversion
A layer of the atmosphere where temperature increases with altitude instead of decreasing. Inversions trap pollutants and moisture near the surface, causing fog, smog, and haze. They also cap thunderstorm development.
Wind Shear
A change in wind speed or direction over a short distance, either horizontally or vertically. Strong wind shear is essential for supercell and tornado development but is also a significant hazard to aircraft during takeoff and landing.
Dew Point
The dew point is the temperature to which air must be cooled to become saturated, so that water vapor begins to condense into dew or fog. The higher the dew point, the more moisture is in the air. In summer, a dew point of 55°F or lower feels dry and comfortable, and 65°F or higher feels muggy.
Zulu Time
Zulu time, written with a Z, is the name used in aviation and meteorology for Coordinated Universal Time (UTC), the time at the Greenwich prime meridian. Weather observations, model runs, and aviation reports all use it so that a time means the same thing everywhere. 12Z is 8 in the morning Eastern Daylight Time and 7 in the morning Eastern Standard Time.
Skew-T: Guides and Explainers
These explainers connect this definition to real-world forecasting and decision-making.
Helpful Tools and Hubs
Use these pages to apply the concept, compare conditions, or follow related weather workflows.
Tool
Wind Chill Calculator
Estimate cold-weather exposure risk from temperature and wind speed.
Tool
Wind Speed Converter
Convert between mph, km/h, knots, and m/s for wind reports and forecasts.
Feature
Advanced Meteorology
Dig into model data, soundings, and pro-level weather analysis in the app.
Tool
Temperature Converter
Convert between Fahrenheit, Celsius, and Kelvin instantly.
Sources
Explore Other Terms
Kp Index
The Kp index is a 0 to 9 scale of global geomagnetic activity, reported in 3-hour intervals from ground-based magnetometers. A Kp of 5 or higher indicates a geomagnetic storm, and the values map onto NOAA's G-scale from G1 (Kp 5) to G5 (Kp 9). The higher the Kp, the farther from the poles the aurora can be seen.
Liquefaction
A process in which water-saturated, loosely packed soil temporarily behaves like a liquid during strong shaking and loses its ability to bear weight. It can tilt or sink buildings, float buried tanks and pipes upward, and cause the ground to crack and spread sideways. Reclaimed land, river deltas, and sandy fill are especially vulnerable.
Tornado
A tornado is a violently rotating column of air in contact with the ground, extending from a thunderstorm. Tornadoes are rated from EF0 to EF5 on the Enhanced Fujita scale by the damage they cause. Most last less than 10 minutes, but the strongest can stay on the ground for more than an hour.
Thundersnow
A rare phenomenon where thunder and lightning occur during a snowstorm. Thundersnow typically happens in intense winter storms and is often associated with heavy snowfall rates of 2-4 inches per hour.
Relative Humidity
The ratio of the current absolute humidity to the maximum possible humidity at the current temperature, expressed as a percentage. 100% relative humidity means the air is fully saturated. Relative humidity changes with temperature even if moisture content stays the same.
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.
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In the WeatherAI App
WeatherAI Pro includes NWS radiosonde soundings for supported U.S. stations, with Skew-T and hodograph analysis, supported stability and wind-profile values, and a 3D hodograph view.
Availability, coverage, update frequency, and alert delivery vary by data source, region, subscription plan, device permissions, and service conditions.