Now-a-days, LR-WPAN i.e. IEEE 802.15.4 is of great use in industrial, residential, medical and military applications. The low data rate enables it to consume very little power. This protocol fulfills most of the criteria of good Wireless Sensor Network (WSN) protocol. In this paper, the performance of IEEE 802.15.4 is studied in various types of WSN by varying the weather conditions. Variation in weather condition is made by covering the sensor nodes by mobile clouds (obstacle) in Qualnet 6.1 simulator .The QoS parameters which are of concern are throughput, packet delivery ratio, average end-to-end delay and energy consumption are studied.