The annual “Sakura Cold”: Don’t be fooled by the daytime sun like I did.

I feel like a fool every single year.

The weather in Saitama/Tokyo has been beautiful lately, and the cherry blossoms are everywhere. But I made the classic mistake: I dressed for the 20°C (68°F) daytime sun and stayed out until evening without a proper jacket.
The night air is still freezing (like 8°C/46°F), and now I’ve officially caught my annual 'spring cold.'

Please learn from my misery—don't forget your layers even if it feels like summer at noon.
How is everyone else coping with these crazy temperature swings? Anyone else currently suffering from the 'Sakura Cold'?