Meteorology: connect observations to developing hazards
Study weather as a physical system, not a list of abbreviations. Air temperature, moisture, stability and lifting interact to produce cloud, precipitation and turbulence. When moist air rises, it expands and cools. Cooling toward the dew point can lead to saturation and cloud formation. A small surface temperature/dew-point spread is a clue to possible low cloud or fog, but it is not a complete forecast. Wind, local terrain, changing airmasses and the availability of moisture also matter.
Separate observations from forecasts. A METAR describes observed conditions at a particular aerodrome and time. A TAF predicts conditions for its stated aerodrome and validity period. Area forecasts, upper-wind information, pilot reports and hazard advisories answer different questions. Read the location, issue time and valid time before interpreting the details. Good weather at departure says little about a destination several hours later unless the route and forecast evolution are also assessed.
Stability helps explain the character of cloud and visibility. Stable air resists vertical movement and often supports layered cloud, haze or steady precipitation when lifted. Unstable air favours vertical development and showery conditions. Thunderstorms require moisture, instability and a lifting mechanism. Their hazards include severe turbulence, lightning, hail and strong changes of wind, including gust fronts that can extend beyond the visible precipitation. Avoid treating a clear patch near a storm as proof of a safe route.
Pressure and temperature affect both the altimeter and aircraft performance. Pressure altitude and density altitude are related but are not interchangeable. A hot day at a high-elevation aerodrome can reduce takeoff and climb performance because the air is less dense. Use the aircraft's approved performance data rather than relying on how well the aircraft flew in cool conditions. Low pressure or cold air can also make true altitude lower than an unchanged or inappropriate altimeter indication suggests; terrain clearance demands particular care.
Use a conservative trend-based decision. Compare current observations with forecasts, note deterioration and identify a safe alternative before departure. Mountain routes, coastal fog and changing frontal conditions may require a larger margin than a simple point forecast suggests. If the actual weather diverges from the plan, reassess early. A timely diversion is a successful decision, not a failure to finish the original route.