1. Western Disturbance over Afghanistan & adjoining Pakistan
The western disturbance as an upper air cyclonic circulation with trough aloft in middle troposphere persisted over Afghanistan & adjoining Pakistan from 11th to 13th December 2017.
The induced cyclonic circulation laid over northwest Rajasthan & neighboring areas at 1.5 km above mean sea level from 10th to 13th December 2017.
Due both the above systems rain/snow occurred at most places over Jammu & Kashmir;, Himachal Pradesh with heavy to very heavy at isolated places on12th & 13th, and at most places over Uttarakhand on 12th& 13th and at many places on 13th. Rainfall also occurred at most places over West Rajasthan on 11th and Haryana, Chandigarh & Delhi, Punjab on 12th and at isolated places over Punjab on 13th and at a few over West Uttar Pradesh & East Rajasthan and at isolated places over West Madhya Pradesh, East Uttar Pradesh and north Gujarat on 12th December 2017.
2. Deep Depression OVER Bay of Bengal (BoB)
Last week’s depression over southeast Bay of Bengal & neighboring areas moved northwards and lay centered at 0830 hours IST of 07th December, 2017, about 870 km southeast of Gopalpur and 875 km eastsoutheast of Machilipatnam and then moved north-northwestwards and laid over southeast and adjoining central Bay of Bengal about 770 km south-southeast of Gopalpur and 800 km to the east-southeast of Machilipatnam at 1730 hours IST, moving in the same direction, it intensified into a deep depression at 0530 hours IST of 08th December, 2017 over central Bay of Bengal and lay centered at 0830 hours IST of 08th December, 2017 over westcentral Bay of Bengal, about 510 km south-southeast of Gopalpur and 610 km east-southeast of Machilipatnam. Moving north-northwestwards it weakened into a depression and lay centred at 2330 hours IST of 08th December, 2017 over westcentral and adjoining northwest Bay of Bengal, about 190 km southeast of Gopalpur and 260 km south-southwest of Paradip. It then moved in a nearly northerly direction and lay centered at 0830 hours IST of 09th December, 2017 over northwest Bay of Bengal, about 170 km east of Gopalpur, 120 km south-southwest of Paradip and 320 km south-southwest of Digha, it then moved north-northeastwards and weakened into a well marked low pressure area over northwest Bay of Bengal at 1730 hours IST of 09th December, 2017 and into a low pressure area over north Bay of Bengal at 0530 hours IST of 10th December 2017 and became less marked in the morning of 11th December 2017.
Due to this system rainfall occurred at many places, with heavy to very heavy rainfall at isolated places occur over Odisha between 0830 hours IST of 8th December & 0830 hours IST of 09th December 2017 and rainfall at a few places over Assam & Meghalaya, Nagaland, Manipur, Mizoram & Tripura between 0830 hours IST of 09th December & 0830 hours IST of 11th December 2017. Heavy rainfall occurred at isolated places over Tripura during the same period.
Dense to very dense fog occurred at isolated places over Gujarat, Rajasthan, Haryana, Punjab, West Uttar Pradesh, Konkan & Goa, Madhya Maharashtra, West Bengal & Sikkim, Assam & Meghalaya, Tripura, West Madhya Pradesh and Odisha on one/two days of the week.
During the week lowest minimum temperature of 1.5°C was recorded at Churu (West Rajasthan) in the plains of the country on 8th December 2017.
During the week, most of the Sub-Divisions of Northwest India, some Sub-Divisions of East & Northeast India and Gujarat Region received excess to normal rainfall. Northeast Monsoon was weak during the week.
During the week, rainfall over the country as a whole was 110 per cent above the long period average (LPA). Northwest India received excess rainfall due to the Western Disturbance over Afghanistan & adjoining Pakistan. East & Northeast India experienced wet conditions due to the Deep Depression over Bay of Bengal. Details of the rainfall distribution over the four broad homogeneous regions of India are given below:
ACTUAL RAINFALL (MM)
COUNTRY AS A WHOLE
EAST & NORTHEAST INDIA
SEASONAL ALL INDIA COUNTRY AS A WHOLE (1ST OCTOBER TO 13 DECEMBER 2017)
For the country as a whole, cumulative rainfall was (-06 per cent) of LPA as on 13th December 2017.Cumulative rainfall was largely deficient over northwest India. Rainfall was excess/normal over the most of sub-divisions of east & northeast India and southern peninsula and few sub-divisions of central India. Details of the rainfall distribution over the four broad homogeneous regions of India are given below: