Temperatures in parts of the UK are set to rise close to 20C later this week and bring the warmest weather of the year so far. However, through this week a warmer southerly wind will draw up air from the Mediterranean and bring temperatures around 6 or 7 degrees above average on Wednesday. For Wales we're very likely to see the warmest day of the year so far with the temperature exceeding the 17. And there's a possibility somewhere in the Midlands, north-west England or north-west Wales could see a temperature close to 20C. 2C - set in London earlier in March. The warmer weather comes in the same week as the start of astronomical spring - or the spring equinox - on Saturday 20 March.