DISCUSSION: For much of the US east of the Rocky Mountain Front Range, the winter of 2019-2020 has not shown much in the way of persistent chilly Arctic air infiltration. Instead, many areas east of the Rockies have witnessed weather patterns found with large-scale ridging (general poleward motion of air associated with high-pressure systems) while the Intermountain West and Pacific coast have remained fairly cool under the influence of large-scale troughing. So what is a potential cause for the unusually warm winter season? One hypothesized answer lies in the unfavorable combination of teleconnections that are currently being observed. An article previously published here goes into more detail on how these teleconnections work so for brevity, the teleconnection patterns responsible will be mentioned in the light of influencing multi-day/multi-week weather patterns as of late.
Now, all teleconnections are important in some degree since they help modulate, or control, the flow patterns across the world. In other words, a certain pattern that favors milder, more stable weather patterns over one part of the world may be countered by cooler, more progressive (stormier) weather patterns downstream, and several of these large-scale patterns are observed at the same time at different parts of the world. But, these teleconnections can undergo changes throughout the course of a year, more so on an inter-monthly time frame. Therefore, the essence of understanding large-scale patterns is to chain information from multiple teleconnections in order to gain a clearer depiction of what is occurring. The Arctic Oscillation, or AO for short (pictured above), has remained predominantly positive. Recall that a +AO pattern yields a tendency to retain colder Arctic air north of the midlatitudes while keeping a zonal flow pattern. In essence, there is limited to no buckling in the mean flow that will help displace cold Arctic air equatorward. The North Atlantic Oscillation (NAO), which corresponds to the phenomena located between Icelandic Low and Azores High, shows as being predominantly positive as well. The East Pacific Oscillation (EPO), after being mostly positive through much of winter, is trending towards neutral and negative values. Normally, the EPO can play a key role in modulating the flow pattern across North America such that -EPO leads to large-scale ridging over Alaska and the Pacific Northwest with subsequent troughing over the northern half of the US. However, this is countered by a negative Pacific/North American (PNA), which encourages advection of polar air over the Pacific coast and intermountain west with subsequent large-scale ridging over the eastern two-thirds of the US. Storm tracks are also favored out west due to the strong grip of a typically dominant high-pressure system over the mid-latitude Pacific Ocean. When putting all of the pieces together, the result favors colder, more progressive patterns to the west and milder, subtler conditions over the east. To see all of the teleconnections described in the article, be sure to visit the Climate Prediction Center’s teleconnection page located here. The science behind the teleconnections and is still a dominant topic in the world of climate science as researchers continue to investigate the impact that different teleconnections have as a unit. There is much to learn about these teleconnections and the interplay between them as certain patterns, such as that of recent, are not always an end-all for distinct weather patterns over the US and the rest of the world. So next time that a weather report indicates longer periods of mild and stable weather or colder and stormier weather patterns, teleconnections may provide clues into the true state of the atmosphere. To find more articles on interesting winter weather topics, be sure to click here! © 2020 Meteorologist Brian Matilla
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 Flooding is the number one natural disaster in the United States (FEMA Mitigation Directorate), causing more property destruction and financial loss than any other extreme weather event. While these hazards are talked about heavily during the summer months, flooding can cause dangerous impacts throughout the year. This is especially true in areas already prone to flooding such as along rivers or lake shores, and those that routinely deal with significant winter weather. For example, substantial melting of snow and ice in early spring can cause devastating results. Similar outcomes occur when rivers and streams are obstructed by large chunks of melting ice, a phenomenon popularly known as an ice jam. Many meteorological and hydrological processes can result in winter time flooding and it is important to be both aware of and prepared for these circumstances.
One way winter weather can contribute to flooding conditions is simply through the rapid melting of heavy snowpacks. Despite melting on the surface, early spring ground temperatures are often still below freezing. In this instance, water is not actively absorbed by the ground beneath and instead flows along the surface toward nearby rivers and lakes, raising water levels and increasing the chance for significant flooding. Flooding is also common as ice from frozen waterways begins to melt, break apart and flow downstream. If these often large pieces of ice approach either a natural or man-made obstruction (such as a river dam), the rivers flow can be impeded. This ice jam essentially blocks the natural movement of a river or stream and causes significant flooding. When the ice jam finally releases, built up water that was blocked from its usual flow rushes downstream and consequently contributes to serious flooding impacts. Currently, not much can be done to prevent ice jams from occurring. However, it is essential for anyone living in areas prone to winter flooding to be aware of the danger and what can be done to minimize potential damage. In addition to purchasing flood insurance, the Federal Emergency Management Agency (FEMA) suggests making a flood evacuation plan and keeping important papers in a safe, waterproof place. Taking these precautionary steps can help reduce loss and destruction even during the most obscure or improbable of flooding scenarios. To find more articles on interesting winter weather topics, click here! ©2019 Weather Forecaster Dennis Weaver |
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