Pampero is the name for a severe line squall that occurs over the Pampas of Argentina and Uruguay. A pampero event marks the passage of a cold front and often brings a considerable drop in temperature. The Pampero is usually accompanied by very humid and close conditions, severe rain, hail and thunderstorms and is followed by a cold, dry, gusty, southerly or south-westerly wind. The first phase is called the Pampero Húmedo (the humid pampero) and the second phase is known as the Pampero Seco (the dry pampero), usually turning into a dust storm the Pampero Sucio. Although the Pampero might occur at any time of the year, it is usuall y strongest during S hemispheric early summer, between October and January. A good example for a severe Pampero happened between 20st and 22nd of October, 2002.
The term pampero itself was introduced by Spanish colonizadores of the Rio de la Plata area. The Spanish colonists were battered by a strong, dry, cold and blustery wind coming from the interior of the continent, the Pampas (prairies) of Argentina. However, the pampero effects are turning milder and less vigorous towards the north.
Synoptically the pampero is caused by a low situated above Patagonia or the Falkland Islands. Coming from the S Pacific the cold front of this depression has to pass the southern Andes losing much of its moisture on the western flanks of the mountain range. The relatively dry and cold air mass clashes into the northerly warm and humid air situated across the Argentine plains north of Patagonia. The situation is very similar to the Great Plains of North America. The cold, dry upper level air and the warm and moist air near the ground eventually trigger a line of supercell thunderstorms, some 50 to 200 km (50 to 150 mi) ahead and parallel of the cold front - the squall line known as Pampero. And yes, even tornadoes are known to occur. The Pampero is usually followed by the warm Zondawind.