Meaning of yellow alert in English:
yellow alert
noun
MilitaryA warning that danger, or an emergency, is thought to be near but not actually imminent; an instruction to be prepared for an emergency; (in "on yellow alert") an initial state of readiness to respond to an emergency; compare sense A. 11 and "amber alert", red alert .
Origin
1940s; earliest use found in The Bismarck Tribune.
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