Ready or not, 'polar vortex' set to make return to DC region

WASHINGTON (FOX 5 DC) - Ready or not, here it comes! Back in December, we warned you that signs were pointing towards the dreaded "polar vortex" returning at some point during the month of January. Strong warming in the stratosphere above the pole right around the New Year's holiday helped split the main "polar vortex," typically present over the Arctic polar region through most of the year, into multiple pieces. It is one of these pieces of the "polar vortex" that will be paying the Midwest and Northeastern United States a visit by the middle of next week.

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Contrary to popular belief, the "polar vortex" is not a new phenomenon. While the meteorological term became a "buzzword" during the extremely cold winters and early springs of 2013-2014 and 2014-2015, meteorologists have used the term for years. However, it is only in more recent years that strides have been made in understanding what leads to a "polar vortex" split. Despite this, there is still a great deal we do not know about them, such as exactly what regions the pieces of the "polar vortex" will visit following a split, although Southeast Canada, Europe, and parts of Siberia are known favorites. What we do know is that they are responsible for bringing some of the coldest are of the winter season to the United States when they do happen to visit.

It should be noted that when we say the "polar vortex" is on the way -- it is not actually going to come and plant itself over our immediate region. We would see record levels of cold if that was the case. Instead, the "polar vortex" will make a close pass, rotating down over the northern portions of the Great Lakes by the middle of next week. Since the unwelcome visitor has traveled southward out of the Arctic, it will bring down a bitterly cold air mass as it does so. The Upper Midwest will take the brunt of it.

Several of the better weather models out there suggest that some all-time coldest temperatures could be challenged in parts of the Midwest. The European model (shown in the first image) suggests that Chicago could make a run at their all-time coldest temperature (-27 degrees from 1985), as would Indianapolis (also -27 degrees from 1994) if air temperatures come in close to model expectations. They may not, however, as the other thing the "polar vortex" will bring down are some strong arctic winds. While these will cause some extreme and downright dangerous wind chills in these regions (30 degrees to 50 degrees below zero in some cases) the moving air tends to keep air temperatures several degrees above model expectations. It is without question that the coldest air of the winter so far is bound for the Midwest and Northeast by the second half of next week.

Here in Washington, DC we are not expected to see things quite to the extreme as our neighbors to the north. You can thank the Appalachian Mountains for their help in acting like a bit of a "cold air dam" for that. However, temperatures, some 20 degrees below normal, are nothing to take lightly. Current expectations are that the vast majority of the time period between next Wednesday and next Sunday would be spent below the freezing mark here in the DC area. The piece of the "polar vortex" would make its closest pass to us on Thursday and Friday, making those two days the coldest mornings. Single digit numbers in some of our northern suburbs, both next Thursday and Friday mornings, seem likely at this point in time, with subzero wind chills likely to threaten as well.

January 2019 is poised to end with some of the coldest air of winter so far for the D.C. region. But of course, the question is, "Can it come with any winter weather?" The leading edge of the cold air will come in Tuesday night into Wednesday. Currently both the American and the European models suggest there could be some snow or a wintry mix as it passes through. However, we have to be very careful with this forecast. Similar to what is occurring on Thursday morning, many times weather models overestimate the speed at which cold air is able to cross the mountains with frontal boundaries such as this one. We have a history here east of the Appalachian Mountains to "rain out" prior to the arrival of the cold air to change the rain over to snow. There is an exception to this rule, however, and that is that if we can develop a wave of low pressure to ride the frontal boundary from south to north, you can "throw moisture back" into the cold air and get a snow event going. It is far too early to tell if that will be the case here. It is something we are watching for now and we'll leave it as a general "threat for rain/snow mix" on the seven-day forecast until we have more confidence. Once the "polar vortex" does take control of the pattern, we tend not to see too much in the way of snow because of how dry the cold air mass is, not much moisture to work with. The best snow lovers could hope for would be a fast-moving clipper system to bring a little light snow to the area, but no strong indications that say that will be the case, just yet.

The Fox 5 Weather Team is here to keep you all ahead of the cold next week and all winter long, and do not forget you can track the cold with us with the Fox 5 Weather App! Free on both the Google Play on Android and the App Store on iOS devices.

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