New Delhi, May 10 -- Frequent, slow-moving western disturbances - essentially, cyclones originating in the Mediterranean Sea and moving east - in the first week of May have resulted in an unusually cool, rainy start to what is usually the peak summer month for northwest India. It has also led to relatively cleaner air in May with all days in "moderate" category so far except one when it dropped to "poor" in Delhi. Now, it emerges that the region may be in for a longer respite: The India Meteorological Department's extended range forecast shows that most of northwest and central India will be cooler than normal at least till May 15, and will receive more rainfall than usual. During the first week of May, nearly 90% of northwest India (combined area of Gujarat, Rajasthan, Punjab, Haryana, Himachal Pradesh, Uttar Pradesh, Delhi, and Uttarakhand) recorded maximum temperatures that were at least 1degC cooler than normal (1981-2010 average). In the same period, the Haryana-Chandigarh-Delhi subdivision received 499% excess rain; Punjab 335% excess; West Rajasthan 926% excess; East Rajasthan 752% excess; and Gujarat 2709% excess. To be sure, the normal levels for this period are very low for northwest India (explaining the high percentages). For example, while the normal rain expected for Haryana-Chandigarh-Delhi is 3.4 mm for May 1 to May 8, the area received 20.4 mm . For the record, the entire northwest has been dry since March 1, receiving 25% lower rain than normal. Rain, thunderstorms, and lightning are likely to continue over northwest and central India for the next four to five days, IMD said on Thursday. "The country has recorded good rainfall activity and widespread thunderstorm activity in the first week of May. This is mainly because of frequent and very slow movement of western disturbances that are causing rain over northwest India. When these systems are moving to the east, they are triggering thunderstorm activity over central and east India. Similar conditions will continue till May 15. After May 15, temperatures will gradually rise," said M Mohapatra, director general of IMD. The weather is peculiar as are the number and nature of western disturbances. "We cannot say that this is unnatural but it is definitely uncommon. The frequency and impact of western disturbances are highest during December, January and February. They continue to pass throughout the year but normally do not frequently affect the Indian region during summer," added Mohapatra. And so, on May 1, which marks the beginning of the infamous Indian summer, Northwest India woke up to gusty winds and overcast skies. "This weather is very unusual in May. Western disturbances are impacting frequently and they are travelling slightly south of their normal position leading to impact on the plains," said Mahesh Palawat, vice president, climate and meteorology, Skymet Weather. Meanwhile, IMD said the southwest monsoon is very likely to advance into the south Andaman sea, parts of southeast Bay of Bengal and Nicobar Islands around May 13. The normal date for monsoon advancement over south Andaman Sea is May 15. "Monsoon advancement over south Andaman Sea is expected a week earlier than normal. But we cannot say if monsoon arrival over Kerala will also be early," said Palawat. Normally, the monsoon arrives over Kerala on June 1. An early monsoon will be the perfect way to end a mild summer...