Rainfall forecast skill of Global Forecasting System (GFS) model over India during summer monsoon 2015

Abstract

The Indian summer monsoon is one of the most important phenomenon that bring vital rain to India, so the Indian summer monsoon forecast and its verification is always of great interest due to monsoons' importance for India’s agriculture. In the present study the categorical (Yes / No) and quantitative verification of rainfall forecast of the Global Forecasting System model running at India Meteorological Department, IMD GFS T574 (25 km resolution) and National Centre for Environmental Prediction, NCEP GFS T1534 is done over Indian domain against 0.25° gridded rainfall observations during summer monsoon season 2015. A detailed verification study for rainfall forecast at 0.25° × 0.25° grid for Indian Window (0 – 40° N and 60 – 100° E) is conducted using two models output; both the / models are indicating that skill of the rainfall forecast is good for all parts of the country except high terrain regions. Regional verification also carried over 5 homogeneous regions of India, i.e., North India, West Coast India, North East India, Central India and Peninsular India using both model outputs. Results show that, in general, both the GFS T1534 and GFS T574 forecasts are skillful to capture climatologically heavy rainfall regions. However, the accuracy in prediction of location and magnitude of rainfall fluctuates considerably. The results documented are expected to be useful to the operational forecasters in day-to-day weather forecasting over Indian monsoon regions.