Hemispheric "Mirroring" Events in 1928 and 1939

[wx_statman]

In this post I'm going to highlight two "mirroring" events, taking place simultaneously in both the Northern and Southern Hemisphere, that occurred in July 1928 and again in July 1939. In both cases, historic heat waves were occurring in the PNW while at the same time historic cold waves were observed in the Southern Hemisphere - in South America in 1928 and in New Zealand in 1939. I don't know how much inter-hemispheric linkage of long wave patterns such as this exists, perhaps the events were linked or perhaps the timing was mere coincidence. In either case it makes for an interesting case study.

 

The events of late July 1928:

 

In the last week of July 1928 a historic heat wave enveloped the PNW. Numerous all-time record highs were set with especially impressive readings east of the Cascades. Wahluke, WA reached 118F on the 24th, setting a state record high (tied at Ice Harbor Dam on 8/5/1961). Other all-time record highs included 116F at Pilot Rock, OR on the 25th, an incredible 114F at Omak, WA on the 26th and 108F at Spokane, also on the 26th (tied on 8/4/1961). Pendleton reached 112F on the 24th and 114F on the 25th, part of a record breaking string of five consecutive days with maximums 108F or higher. West of the Cascades, an all-time record high of 113F was recorded in Grants Pass on the 23rd. Salem had six consecutive days at 96F or higher from the 21st to the 26th, including three straight above 102F. 

 

At the same time the PNW heat wave was winding down, one of the biggest cold waves of the 20th century in South America began to overspread the continent. This cold wave peaked between the 26th and 29th and featured an extremely rare cross-equatorial cold front passage, where an "Antarctic" cold front crossed the Equator moving south to north in the Amazon basin and ultimately reached Venezuela. This has been recorded only a handful of times in the 20th century, including the cold waves of 1957, 1975, and 1995, all of which occurred in July of their respective year. The 1928 cold wave, along with 1957, was the subject of a study in 1964 ("Cross-equatorial cold front passage into Venezuela: 26-29 July 1928; 17-22 July 1957," Myers 1964). This cold wave brought the largest snowfall on record to Curitiba, Brazil (25'25" S; 3,066 feet) when 5 cm (2.0") fell on the city. This was the only snowfall greater than 1 cm in the city's history (this data courtesy of Maximiliano Herrera). 

 

The events of late July 1939:

 

As was the case in 1928, in the last week of July 1939 a historic heat wave once again enveloped the PNW. A maximum of 117F was registered at Umatilla on the 27th, which represents the highest reliably measured temperature in Oregon's history (tied at Pelton Dam on 8/4/1998). This is assuming the 119F readings at both Prineville and Pendleton in 1898 were overexposed, but that's a different subject. Other all-time record highs were set, including an impressive 115F at Kennewick, WA on the 27th, tying the mark first set on August 10, 1898. Illustrating the upper level warmth of this airmass, impressive readings were observed at the higher elevations of the Cascades. Timberline Lodge reached 89F, their highest reading in a period of record from 1938-51. A high of 92F was observed at Stevens Pass, WA on the 26th, their second highest reading in a period of record from 1939-94 (behind 95 on 7/2/1942). West of the Cascades, the heat was also impressive. Medford topped out at 108F and Salem reached 103F, both on the 26th. 

 

On the same date that Umatilla reached 117F - July 27, 1939 - a historic snowfall occurred in New Zealand. This event has been described as the only occurrence in modern times when snow fell across the length of the country, including in subtropical Auckland. From wikipedia:

 

https://en.wikipedia.org/wiki/Auckland#Climate

 

Snowfall is extremely rare: the most significant fall since the start of the 20th century was on 27 July 1939, when snow stuck to the clothes of people outdoors just before dawn and five centimetres of snow reportedly lay on the summit of Mt Eden.

 

For an excellent write-up of the July 1939 snowstorm in New Zealand, read pages 53-54 of the following report:

 

http://www.civildefence.govt.nz/assets/Uploads/publications/tephra-june-2003.pdf

 

Probably the worst storms of this kind in the last hundred years occurred during the winter of 1939 when snow fell the length and breadth of the country during frequent southerly outbreaks from June through to August.

 

 

[Jesse]

Awesome write up!

 

Just out of curiosity, have there ever been arctic cold fronts that make it to the equator and southward?

[wx_statman]

Awesome write up!

 

Just out of curiosity, have there ever been arctic cold fronts that make it to the equator and southward?

 

From what I've read, its never happened. The topography doesn't support it. There have been some close calls though, i.e. the Superstorm of March 1993 produced a wind shift and dewpoint drops on the Caribbean coast of Colombia in its wake, but this is still around 10 degrees N. 

 

The South American topography is unique in that it offers a meridional "funnel" for dense, cold air traveling northward the entire length of the continent. This funnel being the interface of the Andes Mountains and the flat plains to the east. Its similar to how cold airmasses are able to slide down the lee side of the Rockies in North America. In South America the Andes offer cold Antarctic airmasses an unbroken "path of least resistance" from 50S all the way to the equator, and then a bit further north. This is what allows for cross-equatorial penetration, but even then it happens only with the strongest troughs. The biggest one on record was July 1975. A record high pressure system (1044mb in Brazil) pushed a low level cold front all the way into northern Venezuela. It actually capped tropical convection in the region for a week, something that would otherwise never happen. 

 

http://journals.ametsoc.org/doi/pdf/10.1175/1520-0477(1976)057%3C1435:ASHCFP%3E2.0.CO%3B2

 

Good write-up on the 1975 event. 

[snow_wizard]

I'm impressed with the wide variety of topics you are knowledgable on.  I've never even thought of stuff like this.

[wx_statman]

I'm impressed with the wide variety of topics you are knowledgable on.  I've never even thought of stuff like this.

 

Well, my first love was geography. Even before weather! 

 

I'd have to say I'm as interested in geography and history as I am in the weather. 

 

And thank you, btw

[IbrChris]

From what I've read, its never happened. The topography doesn't support it. There have been some close calls though, i.e. the Superstorm of March 1993 produced a wind shift and dewpoint drops on the Caribbean coast of Colombia in its wake, but this is still around 10 degrees N. 

 

The South American topography is unique in that it offers a meridional "funnel" for dense, cold air traveling northward the entire length of the continent. This funnel being the interface of the Andes Mountains and the flat plains to the east. Its similar to how cold airmasses are able to slide down the lee side of the Rockies in North America. In South America the Andes offer cold Antarctic airmasses an unbroken "path of least resistance" from 50S all the way to the equator, and then a bit further north. This is what allows for cross-equatorial penetration, but even then it happens only with the strongest troughs. The biggest one on record was July 1975. A record high pressure system (1044mb in Brazil) pushed a low level cold front all the way into northern Venezuela. It actually capped tropical convection in the region for a week, something that would otherwise never happen. 

 

http://journals.ametsoc.org/doi/pdf/10.1175/1520-0477(1976)057%3C1435:ASHCFP%3E2.0.CO%3B2

 

Good write-up on the 1975 event. 

Yep these events have managed to give record lows in the 50s to near-sea level stations like Manaus and Boa Vista in the Amazon basin. In Portuguese they're known as "friagens" or basically "cold periods". Only example on Earth that I know of where an airmass of clearly polar origins (maritime polar generally) can penetrate the equatorial climate zone.

 

These seem to impact the central Amazon basin mostly, rather than closer to the mouth around Belem and Macapa where record lows below 60 have never been recorded.

 

Looking at some record lows in the central Amazon basin from N to S:

 

Boa Vista: 50 (2N)

Manaus: 54 (3S)

Porto Velho: 45 (8S)

Cuiaba: 38 (15S)

 

However in the eastern basin record lows are much warmer:

 

Belem: 57

Macapa: 67

 

 

 

[IbrChris]

"Although the Amazon region is located geographically close to the equator, the southern part suffers, where appropriate, the action of frontal systems, causing the phenomenon locally known as Friagem (Big Chill). The effect of these polar air raids in the Amazon has been little studied and only the studies of Brinkman and Ribeiro (1972), Hamilton and Tarifa (1978) Fisch (1996) and Marengo et al. (1996) detailed these effects. Fisch (1996) conducted a simple statistical number of Big Chill events in South Pará during the years 1992 and 1993 and obtained a frequency of occurrence of 7 cases per year during the months of May to August. Brinkman and Ribeiro (1972) report that in the case of Central Amazon, occur 2-3 chills per year, during the dry months (June to October). Analyzing the event of a hit region that Chill Manaus (July 1969), Brinkmann and Ribeiro (1972) showed that the event was at the minimum temperature 12 C lower than the climatological average, resulting in strong winds. In the case of variations of climatic elements, Hamilton and Tarifa (1978) analyzed the penetration of an intense cold front (which occurred in 1972), which caused decreases in air temperature in Cuiabá (MT) of up to 13 C. Other important observations are that there is a wind direction change (from north to south), the cloud cover is total and that the event extends to 700 hPa (approximately 3000 m), extending for 3 days. Also regarding the meteorological characteristics of the surface, Marengo et al. (1996) analyzed the spatial extent of changes caused by two mild chills occurred in 1994, noting that the most pronounced effects were obtained in Southern Rondônia (Ji-Parana), in which the air temperature reaches 10 C values, about 8 C below the climatological average. In the central and western regions of the Amazon (Manaus - AM and Maraba - PA, respectively), the decrease of the air temperature was not so great, although the amount of atmospheric moisture has also decreased, inducing that occurred polar air raid (cold and dry). The changes in the vertical structure of the atmosphere were studied by Fisch (1996a), who observed a strong increase of wind speed (mainly in the meridional component), associated with a strong cooling (around 15 C in the atmospheric boundary layer). This information was collected in July 1993, during the course of RBLE the field experiment."


Translated from: http://climanalise.cptec.inpe.br/~rclimanl/boletim/cliesp10a/fish.html

[wx_statman]

"Although the Amazon region is located geographically close to the equator, the southern part suffers, where appropriate, the action of frontal systems, causing the phenomenon locally known as Friagem (Big Chill). The effect of these polar air raids in the Amazon has been little studied and only the studies of Brinkman and Ribeiro (1972), Hamilton and Tarifa (1978) Fisch (1996) and Marengo et al. (1996) detailed these effects. Fisch (1996) conducted a simple statistical number of Big Chill events in South Pará during the years 1992 and 1993 and obtained a frequency of occurrence of 7 cases per year during the months of May to August. Brinkman and Ribeiro (1972) report that in the case of Central Amazon, occur 2-3 chills per year, during the dry months (June to October). Analyzing the event of a hit region that Chill Manaus (July 1969), Brinkmann and Ribeiro (1972) showed that the event was at the minimum temperature 12 C lower than the climatological average, resulting in strong winds. In the case of variations of climatic elements, Hamilton and Tarifa (1978) analyzed the penetration of an intense cold front (which occurred in 1972), which caused decreases in air temperature in Cuiabá (MT) of up to 13 C. Other important observations are that there is a wind direction change (from north to south), the cloud cover is total and that the event extends to 700 hPa (approximately 3000 m), extending for 3 days. Also regarding the meteorological characteristics of the surface, Marengo et al. (1996) analyzed the spatial extent of changes caused by two mild chills occurred in 1994, noting that the most pronounced effects were obtained in Southern Rondônia (Ji-Parana), in which the air temperature reaches 10 C values, about 8 C below the climatological average. In the central and western regions of the Amazon (Manaus - AM and Maraba - PA, respectively), the decrease of the air temperature was not so great, although the amount of atmospheric moisture has also decreased, inducing that occurred polar air raid (cold and dry). The changes in the vertical structure of the atmosphere were studied by Fisch (1996a), who observed a strong increase of wind speed (mainly in the meridional component), associated with a strong cooling (around 15 C in the atmospheric boundary layer). This information was collected in July 1993, during the course of RBLE the field experiment."

 

 

Translated from: http://climanalise.cptec.inpe.br/~rclimanl/boletim/cliesp10a/fish.html

 

That's interesting stuff. A decrease of 15C is no joke in the equatorial regions, whether at the surface or at 850mb. Some equatorial island locations don't see a variance of 15C over the course of an entire year.