Pressure Tendency Calculator
Calculate how fast barometric pressure is rising or falling. Use two readings from the same station to convert your barometer trend into a 3-hour pressure tendency.
NWS pressure tendency is usually reported over 3 hours.
Pressure is trending downward
Falling pressure can point to less settled weather, especially if clouds, wind shifts, or precipitation are increasing too.
Total observed change: -3.6 hPa over 3 hours.
How to Read Pressure Tendency
Rising
Often points toward increasing stability, clearing, or a cooler and drier air mass after a front.
Steady
A weak signal by itself. Look at clouds, wind shifts, dew point, radar, and alerts before changing plans.
Falling
Can suggest a front, trough, or low-pressure system approaching, especially when wind and clouds are increasing.
Source context: the National Weather Service defines pressure tendency as the character and amount of pressure change during a specified period, usually the 3-hour period before an observation.
Use the Same Sensor
Compare readings from the same station or calibrated barometer. Mixing home station pressure, sea-level pressure, and altimeter settings can create misleading trends.
Rapid Change Threshold
The NWS glossary describes rapid pressure rise or fall as 0.06 inches of mercury or more per hour. This calculator flags rapid tendency at about 0.18 inHg, or 6.1 hPa, over three hours.
Pressure Tendency Formula
Pressure tendency equals the current pressure minus the earlier pressure, normalized to a 3-hour change. For example, if pressure falls 2 hPa in 2 hours, the normalized tendency is -3 hPa per 3 hours.
Pressure trend is context, not a complete forecast. It becomes most useful when combined with radar, satellite, wind, humidity, and local alerts.
Put Pressure Trends in Context
WeatherAI combines current conditions, alerts, radar, and conversational weather context so pressure changes are easier to interpret.
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More on Barometric Pressure
Explainers and features that turn a pressure trend into a usable forecast signal.
Guide
Barometric Pressure Explained
What barometric pressure means, how it predicts weather changes, and how to read pressure trends.
Guide
High Pressure vs Low Pressure
How high and low pressure systems work, and why they determine whether you get sunshine or storms.
Glossary
Barometric Pressure
The weight of the atmosphere pressing down on a given point, measured in inches of mercury (inHg) or millibars (mb).
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