There is very little rainfall activity in store for the next 5 days in the Sub_continent, 20th -26th December:
Prominent , among the meager action will be 
1. An easterly wave, weak, and with an UAC embedded in ti moves across Sri Lanka, Westwards from the 21st December to 24th December. Precipitation from the wave will graze through the Southern TN regions. Heavy rains in Sri Lanka from 22nd for a couple of days.
A few showers for Chennai in this period.
2. A weak WD crosses through Northern Pakistan (extreme North) and Kashmir on the 24th.

more details in vagaries..

Some moderate rain is expected over S,S-E Tamilnadu till 22/23-Dec .

Now that the W.D is clear out from North India, a cold wave is expected to prevail for next 2 days over most of N.India.

A weak W.D is expected to affect Kashmir on 24-Dec.

#chennai - records another 24.1 Deg C morning, now (5:14pm) it's clear with stiff breeze from N-E.

Till 8:30am today, S.Tamilnadu got some light rain ... Manimutharu (Tirunelveli dt) recorded 1 CM

Easterlies below 10th parallel over Bay will continue till 24-Dec... http://ow.ly/i/1gG1x

Both COLA and NOGAPS model suggests a circulation to pop over S,S-W Bay on 24 / 25-Dec.. http://ow.ly/i/1gG2v

Till 23-Dec, most of the rain will be over N-E,E,S-E Srilanka and some spill over rain expected for S.Tamilnadu.

IMD GFS model expects a depression over S,S-W Bay on 26-Dec ... http://ow.ly/i/1gG4k 

Today, the 5th parallel circulation is over S-S-W from tip of India ... ow.ly/i/1gFE3

The 5th parallel circulation is expected to enter into S-S-E Arabian sea on 21-Dec... and continue to track West.. http://ow.ly/i/1gFSW

The system is expected to crash into Somalia as a Marked LOW or depression on 24-Dec... http://ow.ly/i/1gFWk