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Unusual Weather Patterns Create Weird Temperatures - December 20, 2015

    T-Shirts and Jeans. That is what many of us here in Maryland were wearing last week as the temperatures hovered around the high 60s and low 70s. Amidst complaints about “not feeling like winter” or “where is the snow?” many of us were baffled by the moderate temperatures this late in December here in Maryland and across the Northeast region. Meanwhile, the west coast is being hit by wet and cold weather; in fact at one point last week Arizona boasted the lowest temperatures in the country. So why are we seeing these strange weather patterns? There is no single answer to that question, but instead a multitude of different occurrences happening at the same time. 

    One of the biggest reasons for the weird weather we have been seeing the past month is El Niño. El Niño effects the entire planet, however it occurs in the central to eastern tropical Pacific ocean, close to the coast of Peru and Ecuador. El Niño is essentially a warming of these ocean waters every two to seven years and the atmospheric rearrangements that occur because of the oceanic warming. During an El Niño event, sea surface temperatures over a wide area of ocean can warm by 1–3°F or more for a period of a few months to a year or two. To qualify as an El Niño event, according to the National Oceanic and Atmospheric Administration (NOAA), sea surface temperatures must remain at or above a 0.5°C (about 1°F) increase for at least three months across a specific region. El Niño can be moderate or strong, with “moderate” events holding at or above a 1.0°C increase, and “strong” events would be at 1.5°C or higher increase in temperatures.

    During an El Niño event, as warm surface water in the Pacific shifts thousands of miles east of its usual location, the storms created by convection above this warm water also shifts. The convection currents also create a rising motion that shifts eastward, causing other adjustments in atmospheric circulation, well away from the tropical Pacific. This results in persistent zones of rising and sinking air which can shift into new locations for months, causing prolonged wet or dry conditions and related atmospheric heating anomalies over vast areas. This atypical heating creates global waves in the atmosphere that radiate away from the ocean warming region termed “teleconnections”, which are large-scale, long-lasting shifts in atmospheric circulation that can affect much of the globe. 

    Here in the U.S., a strong El Niño event has a two pronged effect. First, it tends to produce mild and relatively dry conditions toward the North and Northeast. It also creates cooler and wetter than average conditions in the South and the West coast. In particular, a strong El Niño very often brings more moisture than usual to California, which after years of drought, is a welcome sight. This year we have a strong El Niño event and forecasts expect it to remain in place until spring or summer of 2016. 

    Another reason why the weather has been strange so far this winter is because of the Arctic Oscillation or AO. The AO, also known as the Northern Hemisphere annular mode, is a large scale pattern of climate variability. The AO is characterized by winds circulating counterclockwise around the Arctic at around 55°N latitude. 
 
    The AO has both a positive and negative phase which can affect Northern hemisphere weather patterns. If the AO is in its positive phase, then colder air is confined to the polar regions because of a ring of strong winds circulating around the North Pole. When the AO is in its negative phase, this belt of winds becomes weaker and more distorted, which allows for southward penetration of colder, arctic air masses and an increase in storms in the mid-latitudes. Usually by this time of the year, the AO would bring cold air to the North and Eastern regions of the U.S., resulting in lower temperatures. However so far this year the AO has stayed much farther north, creating a vacuum that warmer air from the south filled in which has helped lead to warmer temperatures. 

    The recent string of strange temperatures has been playing havoc with businesses and companies across the country. Ski resorts in the Northeast are basically empty, with very little to no snow able to accumulate on the mountains through natural or man-made means. Retail stores that rely on in-store customers have seen a loss in profits as well, as many people spent more time outside enjoying the nice weather. According to Planalytics, a weather forecasting firm for retailers, they estimate so far this season mall-based clothing stores have lost around $343 million in sales compared with last year, which is the largest weather-related loss since 1998. 

    This year we have been hit by a “perfect storm,” with both the Arctic Oscillation and El Niño combining to create very strange weather patterns. Couple these two events with climate change and the host of issues that it creates, and it is no wonder that the U.S. weather patterns have been so bizarre. Even if the AO weakens and we finally see cold arctic air reach into the Northeastern U.S., we can still expect atypical weather patterns due to El Niño.


Harrison Jackson is the Education Coordinator for the Maryland Coastal Bays Program.



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