Desai, D S (DDGM-WF Pune, India Meteorological Department, Pune, India)
Westerly troughs which affect Northwest India in mid and upper tropospheric levels [500 hPa, 300 hPa & 200 hPa] more frequently in December, January and February could be traced backwrads to central or west Mediterranean. A few of them could be traced even further west to east Atlantic. During the course of their travel from the Mediterranean to India, the troughs may undergo changes in intensity, orientation, etc. These troughs are sometimes lows originate at the extreme southern end of large amplitude wave trough over central Europe. A few properties of these troughs are discussed here. Theses troughs over Northwest India cause intensification of pre-exinsting low pressure or low level circulations. These systems give rise to heavy rainfall leading to flash floods over Northwest India. A few examples are discussed here.