Cold Waves

Cold Wave

According to Professor Jin-Yi Yu at the University of California, Irvine, a cold wave is considered to be an occurrence of unusually cold air into middle or lower latitudes. Cold waves are particularly more harmful to a city, state, or region than a blizzard, ice storm, or other typical winter hazards due to the vast area this severe weather event can cover.

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For the region Anchorage is located in, cold waves occur when very cold, dense air, near the surface, move out of its source region. This region includes Northern Canada or Northern Asia.

The reason we call this cold air event a “wave” is due to the pattern created during the severe weather event. In the upper-air flow, also called the “jetstream,” a strong ridge-trough is apparent, thus why we call it a cold “wave.”

Meteorologists are able to classify such events as cold waves due to the severe change in temperature from what we consider normal.

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Formation

Due to cold waves occurring all over the world, there is no particular place that is safe from reaching low temperature outbreaks. A cold wave typically forms during the winter months in high altitude, due to the high-pressure center of cold polar or Arctic air masses that form at the surface. Staying relatively shallow, these air masses typically extend to several km above the surface.

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Upper Level Flow

Since a cold wave typically starts in North America, primarily in Alaska or the West Coast of the continent, this is the ideal location for an upper-level ridge. An upper-level ridge, as we know, intensifies high-pressure surface centers.

In an upper-level flow, the high-pressure center of the cold wave is often accompanied with an upper-level convergence, causing the front to be near the surface.

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Equatorward

Cold air masses move from the north towards the equator, this is called equatorward. There are 2 factors to this motion of air flow: (1) cold dense air moves toward warm air and (2) upper-level steering winds. To the east of an upper-level ridge, the upper-level flow steers cold air masses equatorward. Helping intensify this, Pacific cyclones and eastern cyclones affect the upper-level ridge.

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Major Factors for Outbreaks

There are various factors for cold air outbreaks in the United States, one of them very specific to Alaska. Because of the formation of a high-pressure surface center, matched up with a buildup of the ridge in the jetstream over Northern Canada or Alaska, it is common for an outbreak to spread throughout the lower 48 states as well.

Due to the cold winds coming from the north, they are steered by upper-level winds, causing the transport of cold air southeastward, triggering a strong winter cyclone crossing central or eastern North America.

Both of these factors are aided by the remaining threat of snow cover over central North America to keep the polar air masses “refrigerated.”

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Record Temperatures

According to PlantMaps, the record low temperature for Anchorage, Alaska, is -34 degrees Fahrenheit. This is compared to the record low temperature in central Alaska being -80 degrees Fahrenheit, and positive 2 degrees Fahrenheit in the Lower Peninsula region in Alaska. What this tells us is that depending on what region a city is located, the temperature difference can be very different.

According to the U.S. Climate Data, the chart below shows the average low temperature for the city of Anchorage per month:

Jan Feb Mar Apr May Jun
Average high in °F: 23 27 34 44 56 63
Average low in °F: 11 14 19 29 40 48
Av. precipitation in inch: 0.75 0.71 0.59 0.47 0.71 0.98
Days with precipitation: 7 6 7 4 5 7
Hours of sunshine: 78 114 210 254 268 288
Average snowfall in : 11 11 10 4 0 0

 

  Jul Aug Sep Oct Nov Dec
Average high in °F: 65 64 55 40 28 25
Average low in °F: 52 50 42 29 17 13
Av. precipitation in inch: 1.81 3.27 2.99 2.05 1.14 1.1
Days with precipitation: 11 15 15 11 8 7
Hours of sunshine: 255 184 128 96 68 49
Average snowfall in : 0 0 0 8 13 17

Based on this information, we, as a group, have decided that for the city of Anchorage, a cold wave outbreak would be roughly 30-40 degrees lower than that of the average low temperature for each month. We decided on this definition because this creates dangers for the city due to the citizens and city being unprepared for the cold weather for the given month. These dangers will be discussed later.

According to the New York Times, a major weather cold wave to hit Alaska was between January 14 and January 28 in 1989. This was in the midst of the cold wave, which lasted a few more weeks after the story was reported. This wave was reported with temperatures below -70 degrees Fahrenheit. This cold wave was reported to have lasted over two weeks, causing concern for Alaskans.

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According to ”The World Almanac and Book of Facts”, 1989; Pennsylvania State University:

At about -20, motor oil becomes a thick gel and will not move through the engine of a vehicle.

At -40, exposed flesh freezes with a minute.

At -60, exposed flesh freezes within seconds.

At -60 or colder, breath turns to ice crystals that fall to the ground.

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These dangers could affect Anchorage, causing problems with transportation, health, and finance, due to the inability to go to work, provide food, or live in extreme temperatures.

All of these effects of cold waves make it troublesome for Anchorage, as well as the rest of Alaska and Northern Canada because of the frequency of cold air moving through the region.

Sources are hyperlinked, however, here are more sources we gained information from:

https://www.climate.gov/news-features/event-tracker/“winter”-alaska

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