I often remind people that Earth has a split personality. As the Northern Hemisphere experiences winter, it is summer in the Southern Hemisphere. People can be so narrowly focused on where they live that they overlook this fact. It caught my eye that we are currently seeing extreme temperatures on both sides of the ledger right now. Chicago, Illinois is expected to deal with life-threatening and record cold air this week. On the other side of the planet, Adelaide and other parts of Australia are shattering heat records. What is going on?
Chicago is often referred to as the Windy City, but this coming week extreme cold makes its claim for the headlines. According to a CNN wire story on the KDVR.com website,
The forecast models the weather service is referring to have consistently shown numerous days dropping to at least minus-20 degrees or colder next week. For reference, Chicago has had only 15 days ever drop to minus-20 or colder in 150 years of record keeping. There is also the potential that Chicago will see multiple days that fail to reach 0 for the high temperature — something that has happened only twice in the past 20 years, and 22 times in the past 100 years.
The National Weather Service-Chicago tweeted the graphic above warning of life-threatening cold and wind chills in the middle of the work week. What's the cause? It is winter. Because of increasingly infrequent extreme cold events, these events definitely get our attention as they should. Meteorologically speaking, after a low-pressure system brings wintry precipitation to the Midwest United States, a very cold Arctic high pressure system (1040 mb) system settles into the northern Plains by midweek. The low-pressure system is projected to be near the Great Lakes by Wednesday. Meteorology 101 tells us that the circulation around a High is clockwise in the Northern Hemisphere, and the circulation associate with low pressure is counterclockwise. This means the flow pattern and a difference in pressure (a gradient) will cause cold air to spill into the region along with gusty winds. If you look at the weather map for Wednesday (below), you can see some of these features. To visualize the cold stream of air that will flow into the Midwest, simply follow those red lines of constant pressure (isobars).
Because the Earth's Northern Hemisphere is tilting away from the Sun right now, it is winter there. The Southern Hemisphere is receiving more direct, intense energy from our star and is experiencing summer. A graduate school colleague of mine, Richard Henning reminded me, in his social media post, of a lyric from the song "Beds are Burning." In that song, the Australian rock band, Midnight Oil, sings of "steam in forty five degrees." Adelaide, Australia broke an 80-year heat record with a temperature of 46.6 deg C this past week. That value converts to 115.9 deg F. The Bureau of Meteorology, South Australia tweeted on January 24th:
#Adelaide is now the hottest capital in Australia, having just reached 46.6C at 3:35pm, beating the previous record in #Melbourne of 46.4 @BOM_Vic More records: Whyalla 48.5 (prev. record 48.0), Leigh Creek 46.9 (prev. 46.3), and Port Augusta 49.1 (prev. 48.9) #heatwave
Many experts are projecting this to be the warmest January on record in parts of Australia as a brutal heatwave continues. The current heatwave has led to health emergencies, energy crises, fire hazards, and disruptions of the Australian Open tennis tournament. A stagnant area of high pressure situated over southern Australia means sinking, warming air and dry conditions.
Ironically, a recent report issued by Australian government warns of increasing threats from such heatwaves. The 5th biennial State of the Climate report declared that:
Australia's climate has warmed just over 1 °C since 1910 leading to an increase in the frequency of extreme heat events...There has been a long-term increase in extreme fire weather, and in the length of the fire season, across large parts of Australia.
The report also warns of more hot days, heat waves and fewer cool extremes.
Earth is clearly exhibiting its seasonal and hemispheric split personality, but there is something that I want to point out as I close. Extreme events are what we notice not averages. Isn't it ironic that it has become breaking news when it gets cold in Chicago? This is consistent with scientific literature that finds "extreme cold" events becoming less common. Will they continue to happen? Of course. We must look at weather extremes and climate within the proper context. There are many people that draw conclusions based on what is happening where they live or on a given day. That's a no-no.
Stay warm Chicago (or cool Adelaide).
