Marked variations in diurnal and seasonal
range of temperatures occur at all places in the state, exhibiting the
most characteristic phenomenon of the warm-dry continental climate.
The month of March marks the beginning
of summer and the temperature starts rising progressively through April,
May and June. The temperature rise during this period is almost uniform
all over the state. In the western part, mainly at Bikaner, Phalodi,
Jaisalmer and Barmer, the maximum daily temperatures varies between
40oC to 45oC. Occasionally, it rises to 49oC
during the summer months. The diurnal temperature variation is greater
in summers. The minimum daily temperature drops down considerably at
night and remains between 20oC to 29oC. On the
eastern side of the Aravalli range, the day temperatures are in a
similar range but night temperatures hover around 26oC.
At Udaipur and Mount Abu, temperature, however, is relatively lower
and the mean daily maximum temperature in summer reaches 38oC
and 31.5oC, respectively. The daily minimum temperature
for these two stations is around 25oC and 22oC,
The isotherms of summer (June) show variations
from 42oC (Sirohi district) to above 47oC (Ganganagar
district). A major part of the state , comprising the arid zone of
the west and the semi-arid zone of the mid-west, has an average maximum
of 45oC in this month. However, in the south-eastern parts,
the isotherms show a declining trend from 43oC to 37oC.
January is the coldest month of the year.
The winter season remains from December through February with marked
decline in minimum temperatures in December and January. The minimum
temperatures may fall to minus 2oC in the night at some places
like Sikar, Churu, Pilani and Bikaner. A sharp decrease in night temperatures
is experienced throughout the arid and semi-arid zone of western Rajasthan
on account of quick release of thermal radiation from the sandy soil
soon after dusk. Occasional secondary Western disturbances which mostly
cross western, nothern and eastern Rajasthan during winter months, causing
light rainfall, may also lower the night temperatures and increase wind
speed creating wind-chill effect.
The isotherms of winter (January), ranging
from less than 6oC in the north to above 10oC
in the south-east, show few variations in temperatures. The greater
part of Rajasthan, except the south-eastern part of Kota, Bundi and
Baran and the western district of Barmer exhibits the mean temperatures
of more than 10oC. The secondary depressions (western disturbances)
accompanied by the ice-cold winds, emanating from the higher latitudes,
may bring entire Rajasthan under the spell of the cold wave for the
periods of 2 to 5 days during winter months.