Observational aspects of life cycle of a distinct squall line over Assam valley

A squall line of about 180 km in length was observed on 24 th April, 2007 over Assam valley with widespread heavy spells of rainfall and wind speed reaching 70 kmph. An attempt is made to analyze life cycle of squall line including genesis, growth and decay explained by synoptic and meso-scale features. The synoptic features like development of low pressure area with embedded cyclonic circulation at lower levels over Assam, adjoining Bangladesh, Gangetic West Bengal and north –south trough across Assam to northwest Bay of Bengal in mid-tropospheric level in the morning hours were found responsible for it. The thermodynamic parameters like LCL, CCL, and LFC were found as precursor for predicting the severe thunderstorm event well in advance on the contrary Showalter index, Total-Total index, SWEAT index, CAPE and CINE were not found use full as the precursor for occurrence of this particular squall line.