There has been a major stratospheric warming event over the past couple of weeks with a displacement of the polar vortex to lower latitudes and over the next several days a significant high-latitude blocking event will unfold leading to way above normal heights over places like Greenland and northeastern Canada. These large-scale atmospheric events are having an impact on weather patterns all across the Northern Hemisphere. They will be contributing factors to the extreme cold that is about to invade Europe from the east (Siberia) and to a cold pattern that looks like it will develop across much of the US during March which may feature a nor'easter during the transition period late next week.
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While the South Pacific has held its breath over the fate of Bali’s roaring Mount Agung, another volcano in the vicinity has been letting off its own steam. Mount Sinabung is among more than 120 active volcanoes in Indonesia, which is prone to seismic upheaval due to its location on the Pacific "Ring of Fire," an arc of volcanoes and fault lines encircling the Pacific Basin. The volcano in North Sumatra, which has been active since 2010 after centuries of dormancy, had its strongest eruption in five years on Monday morning.
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There is abundant very cold air around in the Northern Hemisphere (e.g., Arctic dips to -76°F) as we reach the mid-point of February and snowfall has been very impressive in recent days from British Columbia-to-Chicago-to-Paris-to-Moscow, but unless the atmospheric flow pattern changes, this abnormal cold and potential snow won’t necessarily come to the eastern US. In fact, the weather pattern in the eastern US has featured multiple mild spells in recent days and little in the way of snowfall for the immediate I-95 corridor, and the overall mild weather pattern looks like it will continue for the next week-to-ten days. After that, however, there are numerous signs that suggest there will be a crucial change to the overall atmospheric pattern over the Northern Hemisphere and this will likely allow for multiple cold air outbreaks to once again be directed into the eastern US.
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One of the ways to monitor the potential for wintertime Arctic air outbreaks in the central and eastern U.S. is to follow what is happening in the stratosphere over the Northern Hemisphere. Sudden Stratospheric Warmings (SSWs) are large, rapid temperature rises in the winter polar stratosphere, occurring primarily in the Northern Hemisphere, and these events have been found to set off a chain of events in the atmosphere that ultimately can lead to Arctic air outbreaks for the central and eastern US that drop southward from northern Canada. Indeed, there is a significant stratospheric warming event now unfolding that will soon result in a dominant polar vortex center over North America - somewhat similar to a major SSW event that took place in January 1985. In that particular year, the major SSW event was soon followed by a period of extreme cold in the central and eastern US.
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We are now experiencing warmer-than-normal weather conditions in the eastern US and there will be mild spells right into the first week of February, but the signs are increasing for a return to a cold pattern next month and it may very well last for an extended period of time. The MJO is a tropical disturbance that propagates around the global tropics and it will be transitioning into “phases” during the month of February that are conducive to colder-than-normal weather in the eastern US. In addition, stratospheric warming will unfold over the next week or so in the polar region of the Northern Hemisphere and this can set off a chain of events in the atmosphere that ultimately results in colder-than-normal weather for the eastern US. There are other signals as well that support the notion of a return to colder-than-normal in the eastern US and it very well could stick around for awhile.
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While the Atlantic Basin experienced a very active tropical season in 2017, global activity was actually below-normal for the year by one type of measurement thanks to quiet seasons in the northern Pacific Ocean and throughout the Southern Hemisphere. The global “accumulated cyclone energy” as we close out the year is 78% of normal year-to-date and there are currently no named tropical storms around the world.
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This is looking like a relatively quiet week across the country compared to last, but next week could turn out to be quite active with storm threats and brutal cold air is likely to plunge into the US from way up north. The bitter cold air mass will first arrive in the Northern Plains by this weekend and then it should spread across much of the rest of the nation during the early part of next week. “Teleconnection” signals support the notion that it turns very cold next week in much of the nation and the new year is likely to start in the deep freeze for many areas.
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Solar cycle 24 has turned out to be historically weak with the lowest number of sunspots since cycle 14 peaked more than a century ago in 1906 and by some measures, it is the third weakest since regular observations began around 1755. This historically weak solar cycle continues a weakening trend in solar irradiance output since solar cycle 21 peaked around 1980 and the sun is fast-approaching the next solar minimum. The last solar minimum lasted from 2008 to 2009 and the sun was as quiet during that time as it has been since 1978. The sun is likely to enter the next solar minimum phase within three years or so. The sun has been spotless for 26% of the time in 2017 (90 days) and the blank look should increase in frequency over the next couple of years leading into the next solar minimum.
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A major pattern change is going to begin on Wednesday in the Mid-Atlantic region and it will result in a period of sustained colder-than-normal temperatures that will assure a much different December compared to the last five. This pattern change to cold will also include increasing chances for snow – perhaps as early as late this week or during the upcoming weekend – as an active upper-level trough forms in the eastern US associated with the initial cold blast.
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If you still have to put up outside Christmas lights and rake some more leaves then this weekend may be the last chance with seasonal temperatures in the Mid-Atlantic region. There are continuing strong signs for a major pattern shift in the central and eastern half of the nation that will bring some serious and sustained cold thanks to a combination of strong high-latitude blocking centered over Greenland, an intensifying upper-level trough in the central and eastern US, and strong high-pressure ridging along the west coasts of the US and Canada. The transition time period from the current mild weather pattern to this upcoming cold pattern looks like it will come around next Wednesday, December 6th with the arrival of a strong cold frontal system in the eastern states that will be followed by a wall of cold.
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