Pressure is the weight of the atmosphere pressing down on everything below it. It’s a force you never notice day-to-day — until it changes. Shifts in atmospheric pressure drive weather systems, shape wind patterns, and determine whether you wake to blue skies or grey drizzle. Understanding pressure readings unlocks one of the most fundamental signals in meteorology.
What is Atmospheric Pressure?
Atmospheric pressure is the force exerted by the weight of air above a given point. Imagine a column of air stretching from the ground all the way to the edge of space — its mass, compressed by gravity, pushes down on the surface beneath. At sea level, this amounts to approximately 1 kilogram per square centimetre — or roughly 10 tonnes pressing down on every square metre of your body.
You don’t collapse under this weight because the fluids inside you exert outward pressure that balances it perfectly. But as you ascend in altitude, there’s less air above you, so pressure drops. This relationship explains why mountain climbers need supplemental oxygen at extreme heights — the thinner air carries less oxygen per breath.
Units of Measurement
Meteorologists use several units interchangeably:
| Unit | Typical Range | Notes |
|---|---|---|
| Millibars (hPa) | 980–1040 | Most common in UK forecasting; standard sea-level pressure is 1013.25 hPa |
| Inches of mercury (inHg) | 29.00–30.80 | Traditional US/UK unit; barometers originally measured mercury height |
| Kilopascals (kPa) | 98–104 | SI unit, increasingly used in scientific contexts |
The Davis Vantage Vue reports pressure in millibars (also called hectopascals — they’re numerically identical). Normal sea-level pressure averages 1013 hPa, but variations of ±30 hPa are common during active weather periods.
How the Davis Vantage Vue Measures Pressure
Unlike temperature, humidity, wind, and rain, the barometer does not sit outdoors. Instead, it lives inside the indoor console unit, measuring the pressure of the air surrounding the console — typically indoors at your home or office.
This design choice has a reason: electronic pressure sensors are sensitive to vibration, moisture, and temperature extremes. Housing them indoors protects the delicate instrumentation from the harsh conditions the outdoor sensor array faces daily.
Because the console could be at any altitude, the raw reading isn’t directly comparable to forecast maps or other stations. The console therefore applies a sea-level correction — it adjusts the reading based on its known elevation (you enter this during setup) to estimate what the pressure would be at sea level. This makes it directly comparable across different locations regardless of elevation.
The sensor itself is an electronic piezoresistive diaphragm — a tiny silicon membrane that flexes minutely under changing pressure. Electrical circuits detect this deflection with precision sufficient to register changes as small as 0.3 hPa, allowing tracking of gradual shifts that signal approaching weather systems.
Reading Barometric Trends
The absolute pressure number is useful, but trend information is far more valuable for understanding what’s coming next. Meteorologists pay attention to whether pressure is rising, falling, or steady — and crucially, how quickly:
Rising Pressure
- Slow rise (gradual over 12+ hours): Indicates improving conditions. High pressure building in means settling weather, clearer skies, and calmer winds.
- Fast rise (sharp increase over a few hours): Often follows a cold front passage. Expect clearing skies but potentially gusty winds behind the front.
- Steady high pressure (consistently 1020+ hPa): Settled conditions, light winds, clear skies in winter (risk of frost), warm and dry in summer.
Falling Pressure
- Slow fall (gradual over 12+ hours): Gradual deterioration. Low pressure approaching means increasing cloud cover and eventual rain.
- Fast fall (rapid decline over a few hours): Significant weather system arriving. Expect rain, stronger winds, and unsettled conditions.
- Steady low pressure (consistently below 1005 hPa): Prolonged unsettled weather, persistent cloud, frequent rain, mild temperatures in winter.
Steady Pressure
- No significant change over several hours: Stable conditions continuing. Whatever weather you have now is likely to persist.
The rate of change matters immensely. A slow, steady fall of 5 hPa over 24 hours suggests a distant system passing through. A sharp drop of 15 hPa in 6 hours signals an aggressive front bearing down quickly.
Weather System Associations
Understanding pressure helps decode what’s happening on larger scales:
High-Pressure Systems (Anticyclones)
- Typical pressure: 1020–1040+ hPa
- Weather: Generally settled, clear, and calm
- Wind: Light and variable, often clockwise rotation around the high in Northern Hemisphere
- Summer: Warm to hot days, cool nights, potential for fog in valleys overnight
- Winter: Cold nights with frost risk, bright sunny days but generally mild
Low-Pressure Systems (Depressions/Cyclones)
- Typical pressure: 980–1010 hPa
- Weather: Unsettled, cloudy, windy, wet
- Wind: Stronger, anticlockwise rotation around the low in Northern Hemisphere
- Structure: Usually contain warm fronts (steady rain) followed by cold fronts (showery rain, gusty winds)
Pressure Gradients
The difference in pressure between two locations drives wind. A steep gradient (pressure dropping sharply over short distance) creates strong winds. A shallow gradient (little pressure difference) produces calm or light breezes. This is why storm warnings often cite rapidly falling pressure — it signals an intense low nearby with steep gradients and consequently strong winds.
Typical Pressure Patterns in the UK and Somerset
The British Isles sit squarely in the path of Atlantic weather systems, creating characteristic pressure-driven rhythms:
West to East flow — Prevailing south-westerly winds carry depressions from Iceland towards the UK. These typically deepen (drop in pressure) as they approach, bringing periods of heavy rain and wind, then fill (rise in pressure) as they move away across Scotland and into Norway.
Blocking highs — Occasionally, a strong high-pressure system becomes stationary over Scandinavia or Greenland, deflecting the jet stream and diverting Atlantic storms north or south of the UK. This can produce extended periods of settled weather lasting weeks — or conversely, cold easterlies if the high sits to the east in winter.
Scandinavian lows — Deep depressions sometimes form over the North Sea or Scandinavian coast, tracking southwards along the east of Britain. These can bring prolonged southerly winds with heavy rain and mild temperatures, particularly in late autumn and early spring.
Mediterranean influences — During summer, subtropical high pressure can push north from the Azores, creating hot, dry conditions across southern England. If a low forms over the Mediterranean and tracks northeast, it may pull humid, warm air up across the south-west, bringing thunderstorm risk.
For Somerset specifically, the combination of Bristol Channel proximity and inland positioning creates subtle nuances. Coastal areas feel the moderating influence of the channel’s relatively stable pressure, while inland locations like Monkton Heathfield experience more pronounced pressure swings as systems pass overhead.
Pressure Extremes and Records
Pressure readings can reach impressive highs and lows during exceptional weather events:
- UK record high (recent decades): Approximately 1040 hPa during intense anticyclones in summer 2018 and 2022 heatwaves
- UK record low (recent decades): Around 953 hPa during Cyclone Daria (January 1990), one of the most severe storms in British history
- Normal annual variation: Most days in the UK fall between 990–1035 hPa
- Storm thresholds: Readings dropping below 980 hPa typically indicate significant gale-force systems
Extreme lows correlate strongly with destructive wind events. Cyclonic systems deepening rapidly — dropping 20+ hPa in 24 hours — often produce hurricane-force gusts and widespread disruption. Monitoring the pressure trend gives advance warning of such events before wind speeds peak.
Pressure and Personal Experience
Beyond forecasting, atmospheric pressure affects daily life in subtle but tangible ways:
- Joint pain — Many people report increased aching in arthritic joints during falling pressure periods, possibly due to tissue expansion in lower-pressure environments
- Headaches — Migraines often correlate with rapid pressure changes; some sufferers track barometric trends to anticipate episodes
- Bird flight — Avian species adjust flight altitude based on pressure; observing bird behaviour historically served as folk barometry
- Indoor comfort — Very high pressure in summer can trap pollutants and increase ozone formation, affecting air quality on hot, stagnant days
- Plant growth — Certain crops respond to pressure-driven humidity and cloud patterns; gardeners in some traditions track barometers alongside almanacs
While these connections remain partially anecdotal, they underscore how deeply pressure variations penetrate daily experience beyond pure meteorology.
Visit the Live Data
Track the current atmospheric pressure on the Today page using the WS40 pressure gauge, displayed alongside temperature and humidity. Visit the Looking Back historical charts to examine pressure trends over recent weeks — you’ll spot the characteristic undulations as highs and lows cycle through the region. The interactive chart builder lets you zoom into specific pressure drops or rises and correlate them with rainfall and wind changes.