"Into next week, a lobe of the polar vortex will hang out over Hudson Bay, Canada," Paul Pastelok, AccuWeather's top long-range forecaster, said. A negative AMO (cooler ocean) is associated with reduced rainfall in the vulnerable Sahel region of Africa. There will still be some bumps in the jet stream, associated with storm systems, at times during late April. The notorious and deadly 2011 Super Tornado Outbreak occurred from April 25-28 when a multi-day round of dangerous storms claimed 321 lives across several states in the U.S. Like 2011, 2020 has started off as an active year in terms of severe weather, and the 34 fatalities from last weekend's violent severe weather pushed 2020 ahead as the deadliest year for tornadoes since 2012, when 68 fatalities were blamed on twisters. Even portions of the southern Plains and interior Southeast will have episodes of chilly conditions that bring the risk of frosts and freezes. The pattern will allow a fairly typical west to east jet stream set up from the Pacific coast to the Atlantic coast, meaning milder Pacific air will filter in across much of the country. As of Wednesday, 67 deaths in 2020 have been attributed to tornadoes. However a colder phase in the Atlantic could bring drought and consequent famine to the developing countries of Africa’s Sahel region. For example, at Chicago, the normal high on April 1 is 53 and the normal low is 34. However, the wintry pattern won't become stuck for too long. Sea-level measurements from tide gauges on the other hand extend back more than 100 years in places. This time in April is no stranger to severe weather. The observations that we do have of the Atlantic overturning circulation over the past ten years show that it is declining. When the AMO is in the warm phase, there are more hurricanes in the Atlantic and droughts in the US Midwest tend to be more frequent and prolonged. And once a pattern change that could usher in more widespread warmth across the Midwest and Northeast arrives, it could unfortunately spawn more frequent rounds of severe weather in portions of the country. Warmth and thus severe weather occurrences are expected to be more widespread than normal for late April, even for this traditionally active time in severe weather season. However the 1970s/1980s were much cooler and there are hints of a transition to a relatively cold period at the moment. 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Pastelok also warned of another potential outbreak associated with an larger storm expected to eye the Central to Northeastern states prior to the end of April. By comparing our sea-level index against the AMO index we were able to provide, for the first time, observational evidence of the widely hypothesised link between ocean circulation and the AMO. This article was originally published on The Conversation. The prolonged negative AMO was associated with the infamous Ethiopian famine in the mid-1980s. Sea-level fluctuations from Florida to Boston can be divided by Cape Hatteras, where the Gulf Stream leaves the coast to flow eastward. Just a touch of snow was enough to trigger multiple-vehicle pile-ups around Chicago during Wednesday morning, and a more general snowfall is forecast to extend from the central Rockies to a narrow swath of the Midwest and into the interior Northeast prior to the end of this week. Once we adjust for overall global warming trends, an oscillation in Atlantic sea-surface temperatures emerges. For example, Atlantic temperatures declined by 0.1ºC per decade from the 1940s to the 1970s. The Atlantic Ocean’s surface temperature swings between warm and cold phases every few decades. By comparison, global surface warming is estimated at 0.5ºC per century – a rate twice as slow. Notifications can be turned off anytime in the browser settings. A substantial warmup is predicted to precede and accompany that late-month storm, helping to set the stage for severe weather. In the UK it tends to mean reduced summer rainfall – the mythical “barbeque summer”. This website uses cookies to improve user experience. The normal temperature trend is increasing at a faster pace this time of year too. The warmth seen in the Northeast and such normally cold cities as … Because the AMO influences a range of climate conditions in different parts of the world, it is important that the mechanisms driving it are properly understood. On average, April yields the third-highest number of tornadoes of any month of the year, behind only May and June, and it is the deadliest month for twisters on average. This a major influence on the wind patterns and the heat transferred between the atmosphere and ocean. The black line represents the ten year average. We now know that accelerations in sea-level rise in cities like New York and Boston on the north-east coast of the US are linked to a cold spell in the Atlantic. Scientists have widely hypothesised that ocean circulation, and in particular the Atlantic meridional overturning circulation which sends warm surface water northward (the Gulf Stream) and deeper cold water southward, drives the phases of the AMO by moving heat around. Since cold air will be more firmly entrenched across the northern tier, there will be opportunities for snow and the likelihood of snowfall for some locations that typically do not get much snow during the middle of April. However, these bumps would not tap into Arctic air, unlike the wintry pattern the nation is enduring now. / ERSSTv3b, CC BY-SA. Sign up today to get weekly science coverage direct to your inbox. The risk of severe weather often follows close behind building warmth and humidity. As a result, we expect the AMO is moving to a negative (colder surfer waters) phase. The pattern will allow a fairly typical west to east jet stream set up from the Pacific coast to the Atlantic coast, meaning milder Pacific air will filter in across much of the country. In our latest research we were able to show that differences in sea level along the US east coast provide a measure of the strength of ocean circulation. Since 2004, we also have continuous, full-depth, basin-wide measurements of the Atlantic overturning circulation with the RAPID monitoring project at 26ºN. By continuing to use our website you consent to all cookies in accordance with our cookie policy. The Cliffs of Moher look out over the Atlantic – but is the ocean endangering us on land? Read the original article. Many studies, dating back to 1938, have used this data to study variations in ocean circulation. "There is the potential that severe weather makes headlines around April 22 and 23 in the South," Pastelok said. ... the coats and gloves are gathering moths right now. In the Pacific Northwest, a positive AMO leads to more rainfall. In this position, waves of cold air will have an easy route from northern Canada to the northern Plains, Midwest and Northeast. "During the fourth week of April (later next week), the polar vortex will retreat northward," Pastelok said. There could be some days where temperatures swing 10 degrees above average or greater, which may correspond to highs in the 70s and 80s in much of the Midwest and in part of the Northeast. We now know that accelerations in sea-level rise in cities like New York and Boston on the north-east coast of the US are linked to a cold spell in the Atlantic. Land has a lower heat capacity than oceans, and it also heats and cools faster than oceans. Even if temperatures just trend back to average late next week and replace the current below-average conditions, that temperature response in the forecast pattern could add 20 degrees or more to daytime highs and 10-20 degrees to nighttime lows. The retreat of the polar vortex could spell trouble for some parts of the country. The difference (south minus north) is representative of ocean circulation, and more circulation means more heat is transported. A cold Atlantic also means fewer hurricanes hitting the southern US. Easter looked more like Christmas across some parts of the United States, and for Americans hoping to put cold and snow in the rearview mirror, the wait will last a while longer. "A second severe outbreak is possible spanning April 27-29, which looks more widespread and farther north than the storms on April 22-23 and would impact areas from the middle Mississippi Valley to the East coast," Pastelok said. Gerard McCarthy is Senior research scientist in Physical Oceanography at National Oceanography Centre.Ivan Haigh is Lecturer in Coastal Oceanography at University of Southampton. By the end of April, the normal high is 65 and the normal low is 44. The ocean went through a warm period in the 1930s/1940s and again in the 1990s/2000s. The bad news, at least if you’re an African farmer or have a coastal property in New England? "This shift will steer the coldest air away from the northern states and prevent future, big, long-lasting cold air invasions from northern Canada and will probably mark an end to snowy episodes in much of the Midwest and Northeast," Pastelok said. AccuWeather meteorologists expect the cold weather pattern to ease up next week. Certainly – and perhaps obviously – the mean temperature of islands downwind of the Atlantic such as Britain and Ireland show almost exactly the same temperature fluctuations as the AMO.