A weather station gives you a detailed record of what is happening at one point on the earth's surface. With experience, you can extract surprisingly useful short-range forecasts from this data — particularly from pressure tendency, wind shifts, and temperature-humidity relationships. The physics behind atmospheric pressure and its relationship to weather systems is well explained by the UK Met Office guide to pressure. This article translates those principles into practical observation habits for station operators, building on the data quality foundations in Station Data Sanity Checks and the instrument standards in Observation Standards.

Pressure Tendency

Barometric pressure tendency — the rate and direction of pressure change over time — is the single most useful forecasting parameter available from a home station. Professional forecasters use 3-hour pressure change as a key indicator.

Rates of Change

• Slow fall (1–3 hPa / 3 hours): gradual deterioration likely within 12–24 hours. Cloud and wind increasing.
• Moderate fall (3–6 hPa / 3 hours): active weather system approaching. Rain or strong wind within 6–12 hours.
• Rapid fall (>6 hPa / 3 hours): intense system approaching. Expect significant wind and precipitation within hours.
• Slow rise (1–3 hPa / 3 hours): improving conditions. Clearing skies, decreasing wind.
• Rapid rise (>6 hPa / 3 hours): strong high-pressure advection. Often follows a cold front passage. Conditions improve but wind may remain gusty.
• Steady (±0.5 hPa / 3 hours): current conditions likely to persist for 12+ hours.

The Pressure Trace

GraphWeather's barograph display is one of its most valuable features. A 48-hour pressure trace reveals patterns that instantaneous readings cannot: the timing and rate of pressure falls, the shape of the recovery after frontal passage, and the diurnal pressure tide (a subtle twice-daily oscillation caused by solar heating of the atmosphere). Learn to read the shape of the curve, not just the current value.

Frontal Passage Signatures

Weather fronts produce characteristic signatures in your station data. Learning to recognise them improves your understanding of local weather evolution.

Cold Front

• Pressure: falls steadily before, then rises sharply after passage
• Temperature: drops abruptly (often 5–10°C in 1–2 hours)
• Wind: shifts from southwest or west to northwest or north (Northern Hemisphere)
• Humidity: drops as cooler, drier air arrives
• Precipitation: brief heavy rain or showers at frontal passage, then clearing

Warm Front

• Pressure: falls gradually over 12–24 hours
• Temperature: rises gradually, sometimes with a distinct step at passage
• Wind: shifts from east or southeast to south or southwest
• Humidity: increases steadily; fog or drizzle common near passage
• Precipitation: prolonged light to moderate rain ahead of the front

Seasonal Considerations

Pressure behaviour varies with season and latitude:

• Winter: larger pressure swings, more active frontal systems, faster-moving systems. The best season for barograph-based forecasting.
• Summer: smaller synoptic pressure gradients. Convective storms (thunderstorms) develop with little pressure warning — they are driven by instability and moisture, not synoptic-scale pressure patterns.
• Transitional seasons: most variable. Rapidly alternating high and low pressure systems make spring and autumn the most interesting seasons to observe.

Limits of Single-Station Forecasting

A single station observes what is happening at one point. It cannot tell you:

• What is happening upstream — you see systems only as they arrive
• Whether a precipitation event will hit you or pass north/south
• Upper-level dynamics that determine system development
• Convective initiation (thunderstorm formation) with useful lead time

For these, you need synoptic charts, radar imagery, and professional forecasts. Use your station data to add local detail and timing to the broader picture — not to replace it.

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