Recommended Stories. The Shawnee News-Star. Raleigh News and Observer. The Weather Network. Bellingham Herald mcclatchy articles. FTW Outdoors. Military Times. The Guardian. Macon Telegraph. CBS News. Associated Press. Now we are speaking in the general sense here. It does mean that it might set up a favorable pattern for more prolonged cold and snow. The black arrows show a cross polar flow. In other words the air is moving from Siberia and the Arctic and into the United States as indicated by the arrows.
The big question is if the split occurs as forecast which is shown to begin around day 9. While that is the long term views, the slightly shorter term view is shown by the European ensemble forecast and it appears bullish as we head into the 7 to 10 day time range. The European Ensemble at day 10 shows a cold polar flow from Canada and an active southern stream. When the Arctic Oscillation and North Atlantic Oscillation are positive, the storm track will move through the central and eastern Great Lakes.
When the Arctic Oscillation and North Atlantic Oscillation are negative, the storm track would be suppressed towards the Mid Atlantic coast and cold air is able to move further south. The winter will come down to this simple question, how frequently will the Arctic Oscillation and North Atlantic Oscillation be negative or positive. This pattern will feature low-pressure systems that enter through the Pacific Northwest and typically redevelop around Oklahoma before moving towards the Tennessee River Valley.
This core storm track would shift towards the eastern Great Lakes or towards the Mid Atlantic coast. This type of storm track is called a Miller Type B storm track. Regional Weather Impacts. An active Polar jet stream will support a series of storms, enhancing snowfall totals over the northern Rockies.
When high latitude blocking is in place, the storm tracks are suppressed south and support more snow and ice. When high latitude block is not in place, the storm tracks are focused further north producing more ice and rainfall events.
Temperatures will be near normal and precipitation will be above normal. Expect significant swings in temperatures from well above normal to well below normal temperatures. REGION FIVE: This region will be on the south side of the active storm track and will feature a high threat for winter severe thunderstorm events and above-normal precipitation and above normal temperatures. An occasional severe thunderstorm outbreak will be possible due to the storm track to the north of this region.
Warming of the stratosphere means that the polar vortex is weakened, and can also collapse under the pressure from the warming event. The source of the warming usually comes from the bottom up, as strong weather patterns can actually deflect a lot of energy upwards into the stratosphere, disrupting its dynamics.
A strong polar vortex usually locks the cold air into the Polar region, creating milder winters for most of the United States and Europe. This creates a chain reaction, which can disrupt the jet stream, and creates high pressure over the Arctic circle, releasing the cold arctic air into Europe and the United States. An SSW event is usually triggered by specific massive pressure patterns in the troposphere, which can send a lot of energy upwards vertically into the stratosphere.
The top row shows the stratospheric conditions, with warming anomalies, and a polar vortex split into two parts. The bottom row shows the surface temperature anomalies, following these events, with the very cold winter in and cooler weather after the SSW event. Looking closer at the warming event, we can see the stratospheric warming red colors as it slowly progressed downwards over time. It eventually connected with the surface, raising pressure over the North Pole, and releasing the colder air into western and central Europe and the northern United States.
If we combine all Stratospheric Warming events and look at the weather days following the stratospheric warming events, we get an interesting picture. We can see below that the pressure usually rises above the Polar regions, and drops over Europe and the western Atlantic. Below we have the corresponding temperature days after an SSW event. Most of the United States is trending colder than normal, and also Europe , with the exception of the southeast parts.
Note: this is an average picture of many SSW events. Each individual stratospheric warming event is different and does not automatically mean a strong winter pattern. To see a practical example, look no further than last winter.
We witnessed strong stratospheric warming this year in early January, which was during a west QBO, and might come as a very slight surprise, as negative east QBO is usually more favorable for such an event. On January 5th, the preliminary date of the Sudden Stratospheric Warming event was marked, as the winds around the polar circle have reversed.
The stratospheric warming wave has crawled over the entire North Pole in the stratosphere, effectively splitting the cold-core of the polar vortex into two parts. One part of the broken polar vortex has moved over North America and one over the European sector. At this point, this does not have much to do directly with the winter weather on the surface, since this is at a 30km altitude.
But the weather influence followed quite soon after. The strength of the polar vortex is usually measured by the power of the winds it produces. We can track this stratospheric warming event by looking at the temperature and wind speeds.
Towards mid-month, and especially towards late December, the polar vortex began to weaken. We can see the stratospheric zonal winds became negative in early January, due to the warming event that collapsed the polar vortex.
Looking at the NASA temperature analysis for the polar stratosphere, we can see the large temperature spike at the 10mb 30km level. This shows a strong warming event, with temperatures staying above normal for weeks after. Rapid cooling began in early February, as the polar vortex recovered some of its strength.
When trying to find a connection between the stratosphere and our winter weather , it helps to have more specialized images at hand. Especially one that shows altitude and time. The image below shows an atmospheric pressure index. Negative values indicate lower pressure blue colors and positive values indicate higher pressure red colors. You can see strong positive values in the stratosphere in early January, associated with the higher pressure buildup during the stratospheric warming event.
This persisted well into February, influencing the weather circulation even when the stratospheric warming was already over.
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