Weather Events

The table below shows the main features of Zonda wind events. The differences in observed weather on the windward and lee sides of the Andes are emphasized.


Parameter Description
Precipitation
  • Precipitation produced by forced orographic ascent on the windward side.
  • Heavy snowstorms may sometimes occur near the mountaintop, leading to road closures.
  • No precipitation on the lee side.
Humidity
  • Extremely dry conditions on the Argentinian side.
  • In the most severe cases, relative humidity may fall below 10% (very high dew point depression).
Temperature
  • Subsidence inversion on the Chilean side caused by a dry and stable subtropical anticyclone above a shallow maritime air mass.
  • Cooling by orographic precipitation and ascent.
  • Strong rise of temperature on the lee side.
Wind (incl. gusts)
  • Perpendicular to the mountain barrier, often with a northwesterly component.
  • Strong and warm winds at the surface on the lee side of the mountains, with intermittent gusts.
Cloud
  • On the windward side stratocumulus, cumulus and altocumulus.
  • Above the mountaintops "cap" or "barrage" clouds.
  • On the lee side occasionally high cirrus, lenticular altocumulus clouds and rotor clouds.
Other relevant information
  • Dust storms are possible in dry regions near the Andes in Argentina, generated by strong winds at the surface.
  • Visibility may fall considerably.
  • The dry conditions and gusty winds favor the initiation and propagation of wildfires.
  • Severe clear air turbulence possible, created by mountain waves.



Schematic of synop observations and turbulence reports during Zonda events.
Surface analysis of 18 UTC 30 Aug 1999. Isobars (solid, hPa), isoterms (dashed, °C) and synop observations. From Seluchi (2003).


Time series of surface observations at San Juan airport during the 23-24 June 2010 Zonda event. Temperature (red), dewpoint (blue) and surface pressure (black). Temperature increase over 30°C and dewpoint decrease about 25°C in 3 hrs period. 35 kt winds and 53 kt gusts caused severe damage to buildings, widespread power outages and wildfires in the region.
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