Plain English Meaning
A small code in a weather report that flags wind direction information, usually showing how much the wind has been shifting around recently.
Full Definition
A remarks-section indicator used in METAR and SPECI weather reports to introduce wind variability information, typically reporting the variation in wind direction over the past ten minutes when the variation is 60 degrees or greater and the wind speed is greater than 6 knots.
Context Anchor
Seen when decoding a TAF that includes low-level wind shear information.
Derivation
The slash is a separator used in coded weather reports to introduce a data group. 'WV' is short for 'wind variability' (or wind in some legacy uses). The slash-letter format flags the of a data element.