Why the origin of cold air is key to how extreme temperatures get in winter
How cold you feel, or not, during the winter depends a great deal on where the air surrounding you originated from.
Year round, there are several primary source regions of air that determine the playing field for temperatures in the United States.
These are the Pacific Ocean, Gulf of Mexico, Maritime, Polar region and Siberian. Below we discuss these source regions from warmest to coldest and how they relate to the weather we feel during the winter months.
Air coming from the Gulf of Mexico
Most often, record warmth during the winter is produced by a flow of air from the Gulf of Mexico.
A Gulf of Mexico air mass is often quite moist. While there either is, or soon will be, rain and fog occurring, there may also be brief episodes of sunshine. The presence of a Gulf air mass to the south can help to fuel moisture to a snowstorm to the north.
Because a gulf air mass is usually only present just ahead of a major storm producing strong southerly winds during the winter, the peak of the warmth and record highs may ignore the time of day.
The New York City skyline gives backdrop to a man jogging along the Hudson River, Thursday, Dec. 24, 2015, in Hoboken, N.J. The temperature topped 70 F in New York City on this day as a flow from the Gulf of Mexico brought record warmth. (AP Photo/Julio Cortez)
High temperatures may occur at night in the winter. For example, temperatures may reach the 60s F in New York City in January near midnight as a storm moves up the Atlantic coast.
Air originating from the Pacific Ocean
When a west to east jet stream pattern is present, storms tend to move across the country in an average of three days. Under these conditions, air from the Pacific Ocean dominates the nation.
This fast flow not only limits the amount of warm, Gulf of Mexico air but also tends to limit the amount of cold air from the north.
This air is mild to begin with as it reaches the West coast and may gain some warmth after flowing downhill from the Rockies and then later the Appalachians.
This type of air mass can bring some record high temperatures, but often it only brings above-average temperatures. For example, highs may be in the 40s to near 50 in Chicago during the middle of January, instead of the 31 F average high.
Pacific air is neither very moist nor very dry east of the Rockies but can be quite moist farther west. If this air mass moves over snowcover or following prolonged cold weather, fog may form, especially over the interior valleys of the West.
When Pacific air is around, the humidity level in your home may be comfortable with fewer problems related to dry skin.
Air streaming in from North Atlantic (Maritime)
Occasionally, during the winter and spring, the routine west to northwest flow of air gets disrupted in the eastern quarter of the nation. When this happens, the flow of air may originate from the Atlantic Ocean and sometimes from the Atlantic waters surrounding the southeastern provinces of Canada.
When a wedge of this air extends southward along the eastern slopes of the Appalachians, a setup for a prolonged period of freezing rain and drizzle may occur as far south as the Carolinas and Georgia.
A man removes ice from his van near Fletcher, North Carolina, Thursday Dec. 15, 2005, after freezing rain coated the area with up to one-half inch of ice. A wedge of chilly, moist air from the Atlantic contributed to the ice storm. (AP Photo/Alan Marler)
This air is cooler than that of the Pacific in the winter.
In a few cases, the air can be dry but most often it is moist and strewn with clouds and drizzle.
For example, temperatures may hover in the 30s in Boston day and night during late February and March when this air mass is in play. The normal high in Boston in late February is 41.
Air plunging from Polar (Arctic) origins
When a north to northwest flow of cold air results in below-average temperatures over large tracts of land, a polar air mass is most often the culprit. Occasionally, this air mass can produce record low temperatures and may be tied to a displacement of the Polar Vortex.
People walked on the frozen Reflecting Pool at the National Mall, Sunday, Jan. 7, 2018, in Washington, D.C. Temperatures ranged from a low of 8 F to a high of 23 on Jan. 7. ( AP Photo/Jose Luis Magana)
This air usually originates from northern Canada and often contains air from north of the Arctic Circle. Sometimes air from the North Pacific may settle over northern Canada and transform by means of extended darkness into a polar air mass. However, most often during the early stages, air from this source region hovers over the middle of the continent away from unfrozen waters of the Pacific or the Atlantic.
Often a polar air mass is accompanied by gusty winds, which may drive AccuWeather RealFeel® temperatures down to frigid and dangerous levels. This air mass often produces heavy lake-effect snow early in the winter and may help fuel blizzards and nor'easters.
A polar air mass can cause frozen pipes and bring freezes to agricultural areas of the Deep South from California to Texas and Florida. High temperatures below zero can occur across the northern tier states. Temperatures may not get above freezing in Seattle and Atlanta when this air is around.
Within a couple of days of its presence, a polar air mass can bring very low humidity levels to homes and businesses. It may be difficult to keep hands from drying out and lips from becoming chapped. This persistent cold, very dry air may also increase the risk of the spread of influenza.
When and where Polar air persists, skiing is often at its best.
The most intense cold waves stem from Siberian (Arctic) roots
By far, the coldest of the cold air masses of the winter originates from Siberia. Technically speaking, this air mass is also Arctic in origin, but from a secondary sense.
Smoke and water vapor rise from chimneys on a frosty morning in Omsk, Russia, Thursday, Jan. 25, 2018. The temperature in Omsk dropped to -30 degrees Centigrade (-22 degrees Fahrenheit). (AP Photo/Dmitry Feoktistov)
Not only is this air frigid to start with, since it began over frozen ground and darkness over north-central and northeastern Russia, but it may also continue to get even colder as it spends more time while moving across the Arctic, before plunging southward over North America.
Siberian air can drop deep into North America when the jet stream extends from northern Asia, over the top of the globe and southward over Canada and the United States. In this case, the Polar Vortex has become displaced well to the south.
While visits from a Siberian air mass may only occur a couple of times a winter and may not occur at all during certain winters, record low temperatures often accompany its presence.
Heat pump systems may struggle to keep up, while tremendous amounts of energy are expended in general. Layered clothing is an absolute must, and exposed skin can freeze in a matter of minutes across the northern tier states.
Temperatures may struggle to get above zero across portions of the interior Northwest, the central Rockies, the Ohio Valley and mid-Atlantic when a Siberian air mass is in the neighborhood.
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