Abstract
The performance of the operational extended-range forecast (ERF) issued by IMD is evaluated for the southwest monsoon 2020. The normal onset of monsoon over Kerala (the southern tip of India) with subsequent rapid progress northward in covering the entire country is very well captured in the ERF with 2 to 3 weeks lead time. The ERF also captured very well the transitions from normal to weaker phase of monsoon in July and the active phase of monsoon during entire August with a lead time of about 3 weeks. The active monsoon condition in the second half of September associated with delayed withdrawal from northwest India was also reasonably well captured in the ERF. Quantitatively, the ERF shows significant skill up to 3 weeks on all India levels. On smaller spatial domains for 36 meteorological subdivisions (met-subdivisions) over India, the performance of category forecasts is evaluated in terms of above normal, normal and below normal. The spatial distribution of the met-subdivision level forecast skill of predicting above normal, normal and below normal categories for the 36 subdivisions during the entire monsoon season of 2020 in terms of correct (forecast and observed category matching) to partially correct (forecast and observed category out by one category) combined categories is found to be 89%, 83%, 80% and 78% for week 1 to week 4 forecasts respectively. The wrong forecasts (forecast and observed category out by two categories) are found to be between 11% in week 1 and 22% in week 4 forecast. Thus, the met-subdivision level forecast shows useful skill and is being used operationally for agrometeorological advisory services of IMD.
Highlights
The forecasting of southwest monsoon rainfall on extended range time scale is vital for issuing reliable advisories to the farming communities of the vast agroeconomic country like India, where the Agriculture production is directly influenced by monsoon performance (Gadgil and Gadgil, 2006)
Since 2009 India Meteorological Department (IMD) has been issuing the operational extended range forecast (ERF) based on multi-model ensemble (MME) from different modeling products viz., National Centre for Environmental Prediction’s (NCEP’s) Climate Forecast System (CFS), European Centre for Medium Range Weather Forecasting (ECMWF) and the JMA’s ensemble prediction model (Pattanaik et al 2013; Pattanaik 2014; Pattanaik et al 2019)
The present ERF system of IMD was initially adopted at IITM Pune, which has the capability of predicting active-break cycle of monsoon which can be used for various applications (Sahai et al 2013, 2015)
Summary
The forecasting of southwest monsoon rainfall on extended range time scale (prediction of active-break cycle of monsoon) is vital for issuing reliable advisories to the farming communities of the vast agroeconomic country like India, where the Agriculture production is directly influenced by monsoon performance (Gadgil and Gadgil, 2006). A recent study by Robertson et al (2019) demonstrated the two weeks ERF issued in real-time during June–September 2018 monsoon period for the four districts of the one of the eastern states of India, viz., Bihar These successful forecasts of onset and break phases during monsoon 2018 over Bihar are related to episodes of the Madden Julian Oscillation (MJO), which the model is shown to capture quite well at [1,2] week lead. Considering the significant importance of ERF in providing services to Agriculture sector the present paper discusses the performance of ERF up to 3 to 4 weeks during the monsoon season 2020 at smaller spatial scales covering 36 meteorological sub-divisions of India
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
