This is from the 10-day weather forecast. As I post this, it is March 9, 2024.
The normal high on these days, the last of which is the final day of Winter 2023/24, is 11C. As you can see, they are predicting a high up to 20C, which is almost double that and is legitimate t-shirt weather.
Even better: Only the first two days would establish new records, as we hit 20C on March 18 five years ago, in 2019.
Anyway, it will make for nice running weather if it happens. Unnerving, weird and unsettling, but nice.