London, the weather is:

taps aff

Taps-Aff (Scots Vernacular) Literally "tops off." The removing of one's shirt in the event of warm weather, a phenomenon rarely seen in Glasgow. Now an expression describing good times being had.¹

Antonym: Taps-Oan, "tops on".
Current Weather: Awright (Partly cloudy)
Temperature: 18°C (64°F)