Barometric pressure is one of those terms you hear in every weather forecast but rarely stop to understand. Yet it's one of the single most powerful indicators of what the weather is about to do — arguably more useful than just knowing the temperature or cloud cover. Once you understand pressure, you start reading the sky in a completely new way.
Here's a plain-English breakdown of what barometric pressure actually is, what different readings mean, and why some people swear their joints can predict storms.
Barometric pressure — also called atmospheric pressure — is the weight of the column of air sitting above you pressing down on the Earth's surface. The atmosphere has mass, and gravity pulls it downward. At sea level, that weight produces a standard pressure of approximately 1013 hPa (hectopascals), or 29.92 inHg (inches of mercury) if you use imperial units.
The term "barometric" comes from the barometer, the instrument used to measure this pressure. Traditional barometers used a column of mercury in a glass tube — as air pressure rose, it pushed mercury up the tube; as it fell, mercury dropped. Modern barometers are digital, but the principle is the same.
Pressure isn't static. It varies by location, altitude, time of day, and most importantly — weather systems moving through your area. That variation is what meteorologists use to predict what comes next.
These two terms are the foundation of weather forecasting. A high-pressure system (often above 1020 hPa) means that air is sinking toward the Earth's surface. Sinking air suppresses cloud formation and tends to bring calm, dry, and settled weather. In summer, high pressure brings heat and sunshine. In winter, it can bring cold, clear nights and frost.
A low-pressure system (often below 1000 hPa) means air is rising. Rising air cools as it gains altitude, and cool air can hold less moisture — so water vapour condenses into clouds. Low pressure is associated with cloud, wind, and precipitation. The lower the pressure, the more intense the weather system can be.
| Pressure (hPa) | System | Typical Weather |
|---|---|---|
| Above 1025 | 🔵 Strong High | Clear skies, calm winds, dry |
| 1013–1025 | 🟢 Normal / Mild High | Settled, fair weather likely |
| 1000–1013 | 🟡 Borderline / Mild Low | Increasing cloud, possible showers |
| 980–1000 | 🟠 Low Pressure | Rain, wind, unsettled conditions |
| Below 980 | 🔴 Deep Low / Storm | Heavy rain, strong winds, storms |
Knowing the current pressure reading is useful, but the trend is even more important. A rapidly falling pressure (dropping more than 5–8 hPa in three hours) is a strong signal that a significant weather system is approaching — expect deteriorating conditions quickly. Meteorologists call this a "pressure fall" and it often precedes fronts, storms, or intense rainfall.
Conversely, rising pressure after a period of unsettled weather signals that conditions are improving. The faster it rises, the quicker the clearance and the more stable the air becomes.
Traditional seafarers and farmers have used this principle for centuries — watching the barometer for falls before heading out to sea or harvesting crops. The rule still holds today.
High pressure creates a natural "lid" on the atmosphere, preventing air from rising and clouds from forming. This is why high-pressure days are often the sunniest and clearest. However, in summer, prolonged high pressure can trap pollution and fine particles near the surface, leading to hazy conditions and reduced air quality.
Low pressure systems draw in air from surrounding areas, causing the circular wind patterns we associate with cyclones, depressions, and frontal systems. The stronger the pressure gradient (the difference in pressure between adjacent areas), the stronger the winds will be. This is why weather maps show isobars — lines connecting areas of equal pressure — and tightly packed isobars indicate strong winds.
This is one of the most common weather myths — and it turns out there's real science behind it. Multiple studies have found a correlation between rapid drops in barometric pressure and the onset of migraines and tension headaches in susceptible individuals. The leading theory is that falling pressure changes the pressure differential across the sinuses and within the fluid surrounding the brain and spinal cord, triggering pain responses.
A 2015 study published in the journal Cephalalgia found that changes of as little as 5 hPa were associated with an increased risk of migraine in some patients. So while pressure changes don't cause headaches in everyone, if you're prone to weather-related migraines, tracking barometric pressure is a genuinely useful health tool — not just superstition.
Similarly, some people with arthritis report joint pain before storms, which may be related to pressure changes affecting fluid and tissue in the joints.
Pressure decreases as you gain altitude because there's simply less atmosphere above you. At the summit of Everest, pressure is roughly 33% of sea-level pressure — which is why supplemental oxygen is needed and why water boils at a lower temperature at high altitude. For everyday purposes, if you live at significant elevation, your local "normal" pressure will be lower than 1013 hPa. Weather apps and stations correct for this by reporting pressure adjusted to sea level, so readings remain comparable across locations.
Understanding pressure is one thing — tracking it for your specific location is another. ClearCast displays the current barometric pressure reading alongside your local forecast, giving you a real-time snapshot of what the atmosphere above you is doing right now.