The overall weather pattern across North America will soon feature strong high-latitude blocking over Greenland and northern Canada and this transition period in the atmosphere will result in a slow-moving and powerful storm over the western Atlantic Ocean by the end of the week. Strong low pressure will head towards the Ohio Valley on Thursday, but then it will become overshadowed by intensifying low pressure over the western Atlantic Ocean and it is this system which will run into a brick wall in the atmosphere as it tries to push to the north. As a result of the blocking pattern setting up in the atmosphere to our north, this strong ocean storm will be forced to the southeast - perhaps in a "looping" fashion - and this will prolong impacts from the immediate I-95 corridor to the coastline. Rain and wind will increase from later Thursday into Thursday night and, as colder air wraps into the system on Friday, there is the chance that some areas generally to the north of the PA/MD border see a mixing with or changeover to ice and/or snow before the precipitation winds down.
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High-latitude blocking refers to an atmospheric pattern in which higher heights (and pressure) compared to normal sets up in high latitude regions such as Greenland or northern Canada and it can remain in place for an extended period of time leading to a large-scale obstruction of surface weather systems. High-latitude blocking tends to be more likely during periods of low solar activity and that is certainly the case now as (weak) solar cycle 24 heads towards the next solar minimum. During the latter stages of winter, this type of setup can result in a persistent colder-than-normal weather pattern for the central and eastern US and perhaps stormy conditions as well. All signs point to a strong high-latitude blocking pattern to develop later this week across the North America side of the North Pole and this virtually ensures winter will not go down without a fight in March in the central and eastern US. This change in the overall pattern will also likely result in the generation of a powerful ocean storm late this week just off the Mid-Atlantic coastline and it will likely be a slow mover.
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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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Record-warmth has been swept away from the Mid-Atlantic region by an overnight passage of a cold frontal system and the next couple of days will stay on the chilly side with occasional rain or drizzle. The weekend will feature milder conditions although still on the wet side and then much of next week looks relatively mild for this time of year. By the end of next week; however, important changes will be taking place to the overall upper-level pattern across North America. A deep upper-level trough of low pressure will begin to retrograde (i.e., move from east-to-west) to the east coast at the same time strong high-latitude blocking forms over northeastern Canada and Greenland. The ultimate result is likely to be a strong storm near the east coast at the end of next week and with colder air potentially wrapping into the system, accumulating snow may very well become a real threat in parts of the Mid-Atlantic region and Northeast US by the first weekend of March.
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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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