Convergence of Synoptic and Dynamical Conditions Responsible for Exceptionally Heavy Rainfall over Uttarakhand, India

Abstract

Fairly widespread to widespread rainfall with scattered heavy falls is rare over Uttarakhand during onset phase of southwest monsoon. This year southwest monsoon onset over Kerala was on 1 June, which is its normal onset date. During initial days of onset of monsoon over peninsular and adjoining central and east India, a low pressure area formed over Bay of Bengal and it moved west-northwestwards. It was one of the causes of early onset of southwest monsoon over the NW India, i.e. on 16 June, 2013 (Fig. 1). The advance southwest monsoon onset over the country during 2013 is the earliest as per IMD record. SW monsoon reached Uttarakhand almost 2 weeks in advance from its normal onset date. Hence the state received early monsoon rainfall. It also caused heavy rain over a larger area over Uttarakhand during 14–17 June, 2013, creating a catastrophic situation at Kedarnath, Badrinath, Joshimath and nearby areas. Sometimes, short wave perturbations moving in the broad mid-latitude westerlies amplify the long wave troughs creating new baroclinic zones in relatively southern latitudes. These baroclinic zones interact with the low latitude circulations and thus leading to development of new circulations in which low level easterlies extend northward over central and northwest India.