A polar outbreak over Buenos Aires
Since Tuesday, May 27, a mass of polar air has been pushing north from Patagonia, bringing a sharp drop in temperatures across much of Argentina. This abrupt weather shift has also triggered the rare appearance of graupel in parts of southeastern Buenos Aires Province, including areas near Buenos Aires City.
According to the National Meteorological Service (SMN), cold air flowing in from the Atlantic Ocean is generating cloud cover and isolated showers across the eastern portion of the province. These showers are expected to be sporadic and interspersed with sunshine, but could also include graupel, a lesser-known type of solid precipitation.
What is graupel and how it differs from snow
Graupel, sometimes referred to as soft hail or snow pellets, consists of tiny white ice granules with a diameter of up to 0.2 inches (5 millimeters). It forms when supercooled water droplets in clouds freeze upon contact with an ice crystal, producing frosty little balls that fall irregularly and lack the solid core of conventional hail.
Unlike snow, which forms deep within clouds as clusters of ice crystals, graupel represents an intermediate form of precipitation, somewhere between snow and hail. It’s also distinct from small hail, which requires strong updrafts inside convective clouds to develop. In contrast, graupel forms under a specific mix of very cold temperatures, sufficient moisture, and vertical air movements that allow ice crystals to grow and become coated in frozen water.
Current conditions and the graupel risk in Buenos Aires
While graupel is rare in Buenos Aires, it can occasionally occur in the southern and southeastern parts of the province during polar air outbreaks. This current cold spell has led to minimum temperatures ranging between 41 °F and 44.6 °F (5 and 7 °C) and persistent southerly winds, creating an environment conducive to the formation of this unusual precipitation.
Even though rain is not expected in the short term, the residual humidity, cold surface air, and unstable skies could support the localized and brief appearance of graupel, especially along the coastal areas. While it poses no material threat, graupel remains a meteorological curiosity in the region, often surprising residents unfamiliar with its soft, icy texture.
This combination of intense cold, lingering moisture, and moderate atmospheric instability may continue to create the right conditions for graupel in the coming days—although any occurrences are likely to be short-lived and scattered.
