Airports are covered by their own forecast product, written in a dense abbreviated code. The format exists because aviation asks a narrower question than the public forecast answers.
The forecast covers a point, not a region
A terminal forecast describes conditions expected within a short radius of a specific airport, because that is the airspace an approach and landing occupy.
A public forecast averages across a county and smooths detail that would be irrelevant to most readers but decisive for an aircraft.
The difference in scale is the reason the two products can appear to disagree while both being correct for their intended purpose.
Only flight-critical elements appear
The code carries wind direction and speed, visibility, weather phenomena, cloud layers with their heights, and expected changes to any of them.
Temperature appears mainly where it affects performance or icing, and elements the public cares about are omitted because they do not affect an approach.
Cloud height is given above the airport rather than above sea level, since what a pilot needs is height above the runway on the way down.
Change groups carry the timing
Rather than a smooth narrative, the forecast is written as a baseline condition with groups describing when and how conditions are expected to change.
Different group types distinguish a permanent change from a temporary fluctuation and from a period of genuine uncertainty between two possibilities.
This structure lets a dispatcher read directly whether the required minimums will hold during the planned arrival window, which is the operational question.
Standardization crosses languages
The format is internationally agreed, so a forecast issued anywhere can be read by a crew from anywhere without translation.
Times are given in coordinated universal time, removing the ambiguity that local time zones would introduce for flights crossing several of them.
The same discipline governs the observation format, so forecasts and current reports use consistent abbreviations and can be compared at a glance.
Passengers feel the product through decisions
Alternate airports must be nominated when the forecast suggests conditions could fall below landing minimums, and that requires carrying additional fuel.
Extra fuel means weight, which can mean carrying less cargo or, in constrained conditions, fewer passengers on a long flight.
A delay attributed vaguely to weather often traces to a specific forecast line that changed a required minimum hours before departure.
Ground handling reads the same product, since forecast freezing precipitation determines whether de-icing crews and fluid supplies must be staged before the first departure bank.