 DISCUSSION: The jet stream marks the boundary between cold polar air and warmer air to the south. In addition, it serves as the storm track along which low pressure centers (i.e., mid-latitude cyclones) tend to move. Currently, the jet stream is dipping down across the center of the U.S. allowing especially cold air to filter farther south than it normally would this time of year. When you combine unusually cold temperatures with mid-latitude cyclones, there is the potential to get snow/ice in places that normally don't see such weather in April. In particular, there are three mid-latitude cyclones that are expected to impact the northern half of the U.S. over the next four days, bringing the potential for snow as far south at Springfield, MO and Washington D.C. as indicated in the graphic above. Many local-scale factors influence snow totals. For example, if the ground is or was recently above freezing, that could contribute to melting and a smaller snow total. If more precipitation falls as sleet or freezing rain, that also would reduce the snow totals. Outside of higher elevations out west, there could be just a dusting of snow up to several inches. The key point is that if you live in the northern half of the country, your might want to keep your winter coats and other winter gear out for a bit longer this season.
To learn more about other high impact winter weather events occurring around the world, be sure to click here! © 2018 Meteorologist Dr. Ken Leppert II
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 DISCUSSION: Now that spring has officially begun, many in the northeast corridor of the United States are recuperating from the major snow storms to have battered the area. These storms are referred to as “nor’easters”. If you live anywhere else in the United States, or anywhere in the world for that matter, you may ask yourself, “what exactly is a nor’easter?” A nor'easter is a strong area of low pressure that often progresses along the Eastern Seaboard of the United States. As the storm system rotates counterclockwise in the storm, the winds tend to blow northeast to southwest over the region covered by the northwest quadrant of the cyclone. They are usually accompanied by heavy rain or snow, and can cause severe coastal flooding, erosion, hurricane-force winds, and/or blizzard conditions. These storms thrive on the convergence of the polar air masses and warmer air over the gulf stream off the East Coast of the United States. Due to the significant difference in temperature of these air masses colliding in the winter months, with the Gulf stream current often pushing near 70 degrees Fahrenheit (21 degrees Celsius), the low pressure that forms tends to be more severe during the predominantly winter months.
So, what has caused all the storms recently in the northeastern United States? It’s fairly uncommon for this area to receive four separate nor’easters of this magnitude in a span of three weeks during March, much alone any winter months. Many local meteorologists in the Boston area such as Danielle Nyles of WBZ-TV as well as Kevin Lemanowicz of Fox-25 have referred to this event as a “four-easter”. This unusual occurrence is caused by the North Atlantic Oscillation, which are fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high in the Atlantic Ocean. Over the past several weeks, there has been a significantly stronger-than-normal oscillation with high pressure stalling over Greenland. When this happens, it is commonly referred to as the “Greenland Block.” With this setup, the jet stream is able to pull warmer air up over Greenland, forcing the cooler air from Canada to push southwards towards the northeastern section of the United States. As the cooler air from Canada is being pushed southwards, this also brings areas of low pressure down towards the same areas. This will create an active storm pattern with the several areas of low pressure. These storms then often tend to regroup over the warm Gulf Stream current off the East Coast of the United States. The blocking high pressure system over Greenland often prevents such winter-time low-pressure systems from moving westward, hence the origin of the name, “nor’easter”. As spring has begun full swing, please keep everyone in the Northeast in your thoughts, as that seems like a pipe dream for them! To learn more about other high impact winter weather events occurring around the world, be sure to click here! © 2018 Weather Forecaster Michael Ames |
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