Today has seen many temperature records go down across the nation with record warmth in the eastern US and record cold in the interior west. In the local area, record highs have already been set at Dulles Airport (IAD) at 71 degrees (1971) and others could fall in the next couple of hours and Wednesday promises to result in numerous record high readings across the Mid-Atlantic. It’ll turn much cooler on Thursday in the Mid-Atlantic region and there will be multiple shots at rain during the late week and weekend; especially, to the north of the PA/MD border. Longer term, signs continue to point to big changes arriving in early March which should lead to more colder-than-normal conditions in the Mid-Atlantic region and perhaps even more opportunities for accumulating snow.
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A fast-moving, but potent system will produce accumulating snow in the DC-to-Philly-to-NYC corridor late tomorrow and tomorrow night and some spots can receive several inches by early Sunday morning. Much colder air pours into the region late today and tonight as NW winds increase in intensity and then low pressure will head from the southern states on Saturday to a position off the Mid-Atlantic coastline by later tomorrow night. Following the winter weather this weekend, much warmer air will flood the region next week and highs by Tuesday and Wednesday may pass the 70 degree mark in much of the I-95 corridor - in other words, the snow will not last for long.
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Even in an overall mild weather pattern, there can be some accumulating snow if the timing is just right between low pressure systems and the usually brief cold air outbreaks that can still take place. We are currently experiencing a mild weather pattern here in the Mid-Atlantic region with 70 degrees possible tomorrow afternoon in parts of the I-95 corridor and there will be another significant warm up in the early-to-middle part of next week, but there is also a shot at some accumulating snow this weekend. A strong cold front will usher in much colder air by the weekend and low pressure will pull out of the southern states on Saturday and head towards the Mid-Atlantic coastline threatening us with accumulating snow as well as ice and rain.
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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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The next couple of weeks promise to be quite active in the Mid-Atlantic region with the likelihood of multiple precipitation events. One of the main culprits to this unfolding active pattern will be a sharpening temperature gradient very cold air to our north and west and moderate air to our south and east. This “battle zone” region will feature many low pressure systems in coming days as the temperature gradient will become a natural draw for moisture.
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The current stretch of generally warmer-than-normal weather in the Mid-Atlantic region that began a couple of weeks ago comes to an end this week and we’ll return to a more sustained colder-than-normal pattern for much of the month of February. One cold front will arrive late tonight and it’ll usher in a cold air mass for the next couple of days and then a second cold front will arrive by early Friday with another cold air mass to follow in its wake - each of these fronts can bring some snow to the DC-to-Philly corridor.
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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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The month of January has been much colder-than-normal so far in the central and eastern US, but there are strong indications that we are about to enter a warmer pattern that may last for the next two-to-three weeks. This does not mean that each and every day going forward in this stretch will be warmer-than-normal and there will continue to be cold air outbreaks, but the cold air outbreaks should be relatively short-lived compared to recent weeks and it'll likely average above-normal for each 5-day period going forward into the first week of February. The latest forecast of the Madden Julian Oscillation (MJO) index is supportive of the idea for an extended period of warmer weather in the central and eastern US. Looking beyond this extended warmer stretch; however, the MJO longer-range outlook and a comparison to some analog years, suggest that a colder pattern is likely to return in February and it could very well stick around for awhile.
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A very active weather pattern has begun and will continue for the next several days. Heavy rain has already fallen today on much of the I-95 corridor and another round will take place later tonight into early Saturday. An Arctic front will pass through the region by early tomorrow and this will result in about a 50 degree temperature drop between now and early Sunday morning in the I-95 corridor as Arctic air floods the area following the warm conditions of today. The rain could end as a period of sleet and/or freezing rain tomorrow morning as the Arctic air arrives; especially, to the north and west of the big cities. Then, after a couple of dry and cold days, snow may threaten the I-95 corridor from later Tuesday into Thursday as low pressure tries to form near the Mid-Atlantic coastline.
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