Here, however, the atmospheric dryness, the nature of the soil and want of vegetation are responsible for the sudden change of temperature from day to night. Although very high temperatures prevail in June, the hottest month of the year is May. Day temperatures in summer shoot up considerably owing to heat waves which sometimes occur over north India. The trying heat and 'loo' hot winds know temporary subsidence through an occasional dust-storm.
Taking the year as a whole, winds from the south west or west are most frequent in Rajasthan. They are strongest in June and lightest in November, but it is semi-arid region comprising Jodhpur, Banner, Bikaner and Ganganagar, which records higher wind-speeds than Jaipur and Kota. Winds are generally light and variable during winter when north-westerly and northerly winds are more frequent. Hot and dust raising winds sweep more or less throughout Rajasthan during the summer and they are experienced in their worst and violent form in the desert areas. During the monsoon season, an easterly wind is always welcome as it promises to bring in rain. The maximum velocity of wind expected in Rajasthan areas is about 85 miles per hour.
The eastern half of the State is more frquented by thunderstorms than the western half. They occur mostly from May to September, particularly in June and July. The dust storms are most frequent in the arid west and decrease progressively over the semi-arid and fertile regions with more rainfall. June is the month of maximum number of dust-storms in the north-western districts. While in the south-eastern areas they occur in May. The number of dust-storms declines rapidly after June; but in the north-west they continue even upto September.
Hail-storms in Rajasthan are rare. Their frequency in Jaipur is maximum, about three in two years, but they are extremely uncommon in the desert area. Ganganagar, for instance, gets only one hailstorm in 10 years while Bikaner, Barmer and Ajmer get one in about three years. Fogs are comparatively more frequent in the arid and the semi-arid areas and occur mostly in the cold months from December to February. They are rare in other areas of Rajasthan except in Jhalawar and Kota where a few days of fog occur in the year, particularly in January.