Weather & Meteorology for Aviation

Why Weather Drives Delays

Ask anyone who has waited out a flight delay why it happened, and weather is one of the most common answers — and for good reason. Unlike a mechanical problem or a crew scheduling issue, which usually affects one aircraft or one airline, weather can simultaneously affect every flight moving through a region: a thunderstorm over a hub airport does not just delay flights landing there, it delays every aircraft that was supposed to depart from there next, and every connecting passenger booked onto those onward flights. Weather is also the one major source of disruption that cannot be engineered away; aircraft, airports, and air traffic control can all be improved, but a storm system still has to pass. That combination — wide-reaching impact and no way to simply wait it out faster — is why weather consistently ranks among the leading causes of delay minutes across the industry.

Reading the Sky: METAR and TAF

Pilots and dispatchers do not guess at conditions; they rely on standardized weather reports issued around the world in a common format, so a report from one country can be read and understood the same way anywhere else. A METAR is a routine report of current conditions at an airport — issued typically every half hour or hour, covering wind direction and speed, visibility, cloud cover, temperature, and any significant weather such as rain or fog happening right now. A TAF, or Terminal Aerodrome Forecast, looks forward instead of backward, predicting expected conditions at an airport over the following hours, typically covering a 24 to 30 hour window and updated several times a day.

Together, a current METAR and a forward-looking TAF let a crew and dispatcher judge not just whether it is safe to depart now, but whether conditions at the destination are likely to still be workable by the time the flight arrives — and whether extra backup fuel and an alternate airport need to be planned for.

The Big Hazards

Several categories of weather concern aviation more than others. Thunderstorms and other convective weather bring turbulence, lightning, hail, and sudden, dangerous shifts in wind, and are generally avoided rather than flown through, which is why a line of storms can force aircraft onto long detours or hold them on the ground until it passes. Fog and other causes of low visibility make it hard for pilots to see the runway during landing, and are one of the most common weather-driven causes of delay at airports prone to it. Icing is a hazard both on the ground, where ice or snow on the wings must be removed before takeoff because it disrupts smooth airflow, and in flight, where ice can build up on the airframe in certain cloud and temperature conditions.

Strong crosswinds — wind blowing across the runway rather than along it — make takeoff and landing more difficult and can force a runway change or a diversion if they exceed an aircraft's limits. Wind shear, a sudden change in wind speed or direction over a short distance, is especially hazardous close to the ground during approach or takeoff. And turbulence, while rarely dangerous to a well-built aircraft, is the hazard passengers notice most directly, and can come from storms, mountains, or the jet stream even in otherwise clear skies.

Landing in Low Visibility: CAT I, II, and III

When visibility drops, airports and aircraft rely on precision instrument approaches to guide a landing safely even when the pilot cannot yet see the runway. These approaches are grouped into categories describing how low visibility can go before a landing must be aborted. A Category I approach permits landing with a decision height — the altitude at which the pilot must be able to see the runway or go around — no lower than roughly 200 feet, with correspondingly modest visibility required. Category II lowers that further, permitting decision heights and visibility down to roughly half of Category I minimums. Category III approaches go lower still, subdivided into levels that allow landing with very little forward visibility, with the most capable variant permitting landing, and even taxiing, in conditions close to zero visibility.

Flying a Category II or III approach requires not just a suitably equipped aircraft and trained crew, but an airport with matching ground equipment — high-precision instrument landing systems and specific runway lighting — which is why not every runway at every airport supports the lowest categories, and why fog can close some airports entirely while others nearby keep operating.

When Weather Somewhere Else Delays You

One of the more counterintuitive things about weather delays is that the storm causing yours might not be anywhere near you. Airline schedules depend on aircraft flying multiple legs in sequence, so an aircraft held up by weather at one airport arrives late for its next flight somewhere else entirely — a delay that can ripple through a whole day's schedule. Air traffic control also manages this at a system level through air traffic flow management, or ATFM: when weather is expected to reduce capacity at a busy hub, such as thunderstorms building over an airport later in the day, controllers may issue ground delay programs that hold aircraft at their departure airports — sometimes hundreds of miles away — rather than let them fly toward a destination that cannot yet accept them.

From a passenger's point of view this can look strange, sitting on a clear, calm tarmac while being told the delay is due to weather, but it reflects the same logic covered in earlier chapters on air traffic control: managing the whole system's flow safely matters more than any single flight's convenience.