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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The overall weather pattern from tonight through the middle of next week will be quite volatile with wild swings in temperatures from the 60’s on Friday afternoon to Arctic cold for this weekend and much of next week. This late week "January thaw" will also result in heavy rain for the I-95 corridor and thunderstorms could even get mixed into the picture as well as some patchy fog. As Arctic cold arrives in the big cities on Saturday morning, the precipitation could mix with or change to ice and/or snow before ending by mid-day. Then, after a couple of dry and quite cold days, accumulating snow may threaten the I-95 corridor from later Tuesday into Wednesday as a reinforcing Arctic blast arrives in the eastern US.
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The stretch of weather that began just before Christmas Day has been very cold relative-to-normal for much of the eastern two-thirds of the country and it may reach a nadir this weekend. Temperatures during the next couple of mornings in the DC-to-Philly-to-NYC corridor should rather easily drop to single digits and some spots will likely reach zero or even sub-zero conditions. Each morning this week has featured numerous record-low temperatures in the Northeast US, Midwest and Mid-Atlantic regions and that pattern should continue tomorrow morning and perhaps become even more widespread early Sunday morning. It’ll stay very cold on Sunday, but less painful than Saturday as temperatures will climb a bit and winds will drop off in intensity and then there will be more modification on Monday with many areas attempting to climb above freezing for the first time in many days. More significant warming in the I-95 corridor is likely late next week for a few days and then an even greater and more widespread “January thaw” is possible later this month.
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A high impact weather event continues for much of the eastern US with bands of accumulating snow soon to be followed by extreme cold and dangerous sub-zero wind chills. This storm now ranks as one of the most intense east coast winter storms ever in terms of how fast and how much it has intensified while moving over the relatively warm waters of the western Atlantic Ocean (i.e., Gulf Stream). In fact, the central pressure dropped 54 millibars in a 24-hour period reaching major hurricane-like strength (category 3) by 7AM of 954 millibars (28.17) and it is unleashing hurricane-force winds along coastal sections of New Jersey to New England. Heavy snow bands rotating around the storm will continue for the few hours in the Mid-Atlantic region, but by later today, the powerful winds will become the main factor and then the extreme cold.
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