Definition
Significant weather, airspace, or operational information that may influence the pilot to alter, delay, or cancel a proposed flight. In a standard weather briefing, adverse conditions are reported first so the pilot can decide whether to continue planning or change the flight before reviewing the rest of the briefing.
Plain English
Anything along your route bad enough that you might want to change your plans, delay the flight, or not go at all. The briefer tells you about these things first so you can make that call early.
Context Anchor
You encounter this term during a preflight weather briefing, especially when the briefer gives early warnings about problems along your planned route.
Derivation
From the Latin adversus, meaning 'turned against' or 'opposing.' In aviation it keeps that sense: conditions that work against the flight as planned.
Why Pilots Care
Adverse conditions are placed first in a briefing on purpose. If thunderstorms, icing, low ceilings, or a runway closure make the flight unsafe or impractical, the pilot can stop planning right there instead of working through the rest of the briefing for a flight that won't happen.
Intuition Check
Do not read “adverse conditions” as just “bad weather.” In a flight briefing, it can also include airport closures, airspace problems, traffic delays, or anything else significant enough to affect the flight.
Example Sentence 1
The briefer began with adverse conditions, noting a line of thunderstorms moving across the planned route.
Example Sentence 2
With no adverse conditions reported, the pilot continued with the original departure time.