THUNDERSTORM SEASON

  Its really interesting. The Pre-monsoon season or Hot weather or Summer season is the names you would have heared it in your text books for the period of March to end of May month. The temperatures, particularly the maximum, during this season are very high over most parts of the country.

Thunderstorms, considered as tertiary atmospheric circulation, are local storms characterized by swift upward movement of air and heavy precipitation including both rainfall, hailstorm and squall with cloud thunder and lighting.

“Fundamentally, the thunderstorm is thermodynamic machine in which the potential energy of latent heat of condensation and fusion in moist conditionally or convectively unstable air is rapidly converted into kinetic energy of violent vertical air currents with associated torrential rain, hail, gusty surface squall winds, lightning and thunder…..A thunderstorm is therefore an instense instability outbreak” (G.T. Treawartha, 1954).

Thunderstorms have many different names.viz.

1) Mango Showers in Kerala, Karnataka Tamil Nadu

            Mango shower occurs along Kerala, Karnataka and also in parts of Tamil Nadu. The showers prevent the mangoes from dropping prematurely from trees and are crucial for the mango cultivation in South India. It is mostly caused by an Line of Wind Discontinuity (LWD). During April-May, the wind direction is in transformation stage to westerlies this will result in the wind from Easterlies to meet the westerlies. This causes trough / LWD across large areas in peninsular India. Massive thunderstorms develop and thus causing thunderous rains. Some places record 100 mm rainfall with ease. Hailstorm (Alangankatti mazhai are associated during this period. In Tamil Nadu, Interior and southern regions get rains during this period.

2) Cherry Blossom’ or ‘Coffee showers’ in Karnataka

              It is a local wind that blows over the interior Karnataka (Kodagu, Chikmagalur and Hassan in Karnataka) during the hot weather season and is extremely helpful for coffee cultivation. Its mostly due to the katabatic wind which blows down the slope toward the valley and when it interacts with the easterlies and causes unstability. The Hill slopes in the interior Karnataka gets most of these rains.

3) Kali Andhi

Hope you all remember last year Andhi that killed many people https://en.wikipedia.org/wiki/2018_Indian_dust_storms in the north India. Puzhuthi puyal. It is just like our Veppa Salanam rains in Tamil Nadu one difference is that it will a gust front filled with sand and then followed by rains with thunder and lightening. Convective dust-storms occur over northwest India during the premonsoon season (March – May). The dust is raised by the down-draft of a thunderstorm cloud (cumulonimbus) or a squall line. ‘Andhi‘ is the local (Indian) name for the convective type of dust-storm, a name possibly given because of the darkness created by the dust-wall as it passes. The distance between the cumulonimbus cloud and the associated Andhi dust-wall on the ground can be as large as 30 Km. The dust raised by strong wind reduces horizontal visibility to less than 100 meters. It may quickly build up out of the blue, transforming the dry hot afternoon into a dark brown mush. The assault of the Andhi usually lasts only a few minutes. North India including Delhi often get affected by these Kali Andhi every year. They are also called as black storms.

4) Loo winds, North-western, India

The Loo mainly originates in the large desert regions of the northwestern Indian subcontinent: the Great Indian Desert, the Cholistan Desert and the desert areas of Southern Balochistan. The plains of North India and Pakistan are both very hot and extremely dry during this season, water evaporates quite readily. Loo direction is from west to east and they are usually experienced in the afternoons and its temperature varies between 45°C to 50°C. Entire North and north west India gets affected by Loo. It makes life miserable for the people and the heat wave takes its toll and many people die because of it.

Kalbaishakhi, West Bengal, India

  It is a other name of Norwestor in West Bengal. Moisture inflow from bay of bengal coupled with the heating of air, cold advection at 500 hpa and and presence of a jet stream between the levels 300 mb and 200 mb are extremely helpful for the occurrence of nor’westers. They normally form over Jharkhand and Bihar and travel entire East India affecting Odisha, West Bengal, Bangladesh. The dooars in West Bengal gets worst hit. Buxa Duar gets close to 900 mm rainfall during the Norwestor season. If you track the radar u can spot derechos and most of the Tornados in India form in this period.

Bordoichila, Assam

It is a other name of Norwestor in Assam. The local severe storms of Assam and North East India during the pre-monsoon season are termed as Bordoichila, meaning the angry daughter of Assam. Advection of warm air in the lower levels and cold air in the upper levels increases the conditional instability in the atmosphere and favor the outbreak of severe thunderstorms.

                                     The southerlies approaching the north–east India, originate from the Bay of Bengal and thus, are warm and moist On the contrary, the westerlies originating from the Tibetan plateau and eastern Himalaya are cold and dry. In night time the Garo, Khasi and Jaintia hills cool down more rapidly than the plains, the katabatic wind blows down the slope toward the valley. This, in turn, brings  down the moist air to the valley and a front-like structure develops during the nighttime, having two different types of air masses on—either side and this causes severe thunderstorms to occur over the valley mostly during the nightime. North Eastern states mostly, Assam, Meghalaya Tirupura gets affected by these storms.

You should also know how dangerous these thunderstorms can be, due to high energy they get because of heat, it kills more people than Cyclones in India every year.