Why is Kerala and rest of south so cold these days

Kerala and the rest of south have been unusually cold these days. While this kind of weather is common in north India, it is something new for the south. Experts blame it on the Polar Vortex. Add to this, the western disturbance. Besides, the absence of humidity and clouds during this period, making the temperatures extreme during day and night. This is why Munnar saw sub-zero temperatures last week