Unlike the stormy remnant of Cyclone Ditwah near Chennai earlier this month, cold waves can’t linger. Instead, if they’re happening over and over, it must be because the ingredients required for an unusually low nighttime temperature are also staying in place. And over Telangana right now , the India Meteorological Department (IMD) has pointed to a combination familiar in winter: dry air, clear skies, and continental winds.

The air mass over Telangana State has been unusually dry of late. When humidity is low, the atmosphere holds less water vapour, which is one of the main greenhouse gases near the surface. With less water vapour to trap heat, the ground loses energy more efficiently after sunset. Clear skies strengthen this effect because clouds that might otherwise absorb and re-ra

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