It has been a wild week for temperature extremes with the amazing heat wave in north central Siberia juxtaposed with an unusual cold spell in portions of Brazil, Bolivia, and Argentina occurring simultaneously almost exactly opposite one another on the planet.
South American cold snap
Between 20-25th July a mass of very cold air suddenly froze a large area of southern South America (where temperatures had been running above average for weeks prior to the abrupt change).
Snow was recorded for the first time since 1996 at Catamarca, Argentina (28°S and located at about 500m/1,650’), and cold rain (temperatures of 5-6C/41°-43°°F) at sea level altitudes like Florianopolis, Brazil. Montevideo, Uruguay also experienced rain with temperatures as low as 3C (37°F). The town of Campos Novos, Brazil (at an elevation of 947m/3,100’) had a high temperature of just 3.6°C (38.5°F) and low of -2.7°C (27.1°F) on July 23rd, a daily average of almost freezing (0.9°C/32.8°F). There was no precipitation at the site that day, if so it probably would have been snow. In fact, a little snow was reported in Brazil in the hills above nearby Curitiba for the first time since 1975.
Snowfall in the mountainous region of Santa Catarina, Brazil is not so unusual. Above is an image of a deep snowfall near Rio Grande do Sul during the cold wave of July-August 2010. Ironically, this occurred at the same time as the famous Moscow heat wave of that summer, a somewhat similar situation as is now occurring. Photographer not identified.
There were incredible temperature contrasts in Bolivia (which isn’t unusual given the complex Andean topography) but what was unusual was that it was actually colder at the low elevations in the Amazonian jungle than in the higher mountainous terrain of the country: temperatures at Bolivian locations above 4000m (13,000’) on 23 July were higher than those in the Bolivian portions of the Amazon jungle at low elevations. For instance, the temperature at Reyes (located at 14°S and 140m/462’ elevation) had a maximum of 9.3C/48.8°F while at El Alto Airport, La Paz (elevation 4,000m/13,200’) the temperature maximum reached 13.9°C (57°F). Temperatures in the Chaco region of Bolivia were remarkably chilly with a reading of -5.8°C (21.6°F) observed at Villamontes.
Some places in the middle of the Andes, protected by mountains on all sides, like Cochabamba didn't experience a single degree drop in temperature, while low areas experienced drops as high as 22-25°C (40-45F) in 24 hours. In Paraguay sleet was recorded in Itapua and the minimum temperature reached -5.2C (21.6°F) at Prats Gill on 24th, not far from the all-time national record of -7.5C (18.5°F) (also set in Prats Gil) on July 13, 2000
The cold air actually filtered as far north as the western part of the Amazon jungle near the Equator, with 7°C (44.6°F) at Rio Branco, Brazil (10°S latitude) and 16°C (60.8°F) at Leticia, Colombia (4°S latitude). Both are low-level sites in the Amazon Basin.
The most exceptional cold wave, in regard to how north cool air has ever penetrated, was that of July 1975 when air of polar origin reached the Caribbean affecting the whole of South America (including the extreme western part of Amazon in Peru, Brazil, Colombia, Venezuela, the Guyanas, and even Trinidad and Tobago. Unlike other cold waves (such as those of 1955, 1973 and 2010) the July 1975 event didn't stop south of the Equator, but continued well into the Northern Hemisphere. This remains unique and the only documented occurrence of such an event. The surface high pressure reached 1044 hPa (30.82”) over central South America on July 15, 1975, the highest yet measured (modern records) on the continent (REF: Markgraf, Vera Interhemispheric Climate Linkages p. 37)
500 mb MAP
Surface air temperature anomaly for the week of July 19-24 (top map) and 500 mb height anomalies for the same period (bottom). Note how the cold air over South America is almost exactly on the opposite side of the world from the heat dome over north central Siberia. NCEP/NCAR maps, courtesy of Stu Ostro.
The cold snap this past week was caused by a strong upper-level low centered over the southern third of the continent. Curiously, it has been unusually mild over the portions of Antarctica opposite South America with a high of 7.8C (46.0°F) being recorded at Base Esperanza (63°S), higher than the normal summer average maximum and just 1.5°C less than the Amazonian maximum of Reyes in Bolivia at 14°S latitude!
Meanwhile on the other side of the world…
The unrelenting heat wave in north central Siberia continues with Svetlogorsk (on the Arctic Circle) recording its 13th consecutive day (as of July 26) with temperatures above 30°C (86°F). Meanwhile, all eyes are turning to Western Europe where a potentially historic heat wave is expected to develop this weekend and continue into next week! There is a chance that some all-time national heat records may fall in some countries like Germany, Liechtenstein, Austria, Slovakia, Slovenia, and Hungary when all is said and done.
Phenomenal Rainstorm in Thailand
On a side note, a historic rainstorm has caused serious flooding in portions of southeastern Thailand. Chantaburi picked up 445.7mm (17.55”) of rain on July 23rd with an amazing 385mm (15.16”) of this falling in just 12 hours and an even more amazing 297 mm (11.69”) in just 6 hours! This may be one of the (if not the) heaviest 24-hour rainfall on record for Thailand (previous record was 414.8mm (16.33”) at Ko Samui on March 28, 2011. A famous flood in Bangkok occurred on May 9-10, 1986 when 401.1 mm (about 16”) of rain fell in just 8 hours. The ensuing floods almost cost the mayor (Chamlong) his job.
METARS for Chantaburi, Thailand July 22-23 when a peak 24-hour rainfall amount of 445.7 mm (17.55”) accumulated, a possible national record. Flooding continues as more rain has since fallen over this region of southeastern Thailand. From OGIMET.
KUDOS: Thanks to Maximiliano Herrera for much of the above information about the cold wave in South America.
Christopher C. Burt
Weather Historian
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