Winter Storms: The Deceptive Killers

Transcription

1 Winter Storms: The Deceptive Killers Matt Baraby Dr. Scott 09/23/03 Environmental Hazards

2 Winter in North America brings dropping temperatures and the chance of several different types of winter storms. Winter storms create environmental hazards that are often overlooked due to the beauty of the winter landscape until we find ourselves caught in a very dangerous situation. Winter storms of varying magnitude and severity affect most regions of the United States on a seasonal basis bringing frigid temperatures, winds, snow, and ice that create situations hazardous to life and property. The key to preparedness for any environmental hazard is knowledge, forethought, and decisive action can be the difference between survival and demise. To build a knowledge base this paper will focus on the types of winter storm how they form, there magnitude, duration, spatial extent, some impressive historical and recent storms, and how mitigation may reduce the impact of winter storms. Winter Storms in North America form in a variety of ways. All winter storms derive there energy from the collision of warm and cold air masses of differing moisture levels. In order to form and gain power a winter storm needs three main components cold air, moisture, and lift created in several ways as moisture rises to the upper atmosphere forming clouds and precipitation. The normal formation of storms that affect the east coast of the United States form as cold dry air from Canada moving south

3 and east on the jet stream collides with warm moist air moving north and slightly east out of the Gulf of Mexico. The position of the jetstream over The United States which usually is elevated from between the south/mid- Atlantic during the spring and summer months to from the Midwest across the northeast during the winter months. This positioning of the jetstream which forces the cold dry Canadian air across the northeast is the reason why precipitation in this area is most often snow, while the farther south you move the precipitation is more likely to be sleet, freezing rain, or just a cold rain. The area where an air mass collides is called a front of which there are three types. A cold front is one in which a large strong advancing cold air pushes warm air along in front of it. A warm front is one in which a strong warm air mass pushes against and over the top of a cold air mass due to the fact warm air is less dense than cold air. A stationary front occurs as a stalemate between the colliding warm and cold front and neither air mass is advancing. We often here about a type of winter storm called lake effect that most often occurs around the great lakes. This type of storm forms as a front moves over a body of water picking up large amounts of warm moist air to the front creating massive snowfall and other precipitation around the lakes shore areas. If you have ever seen snow capped peaks you have seen another type of winter storm phenomenon that occurs in mountainous

4 regions called mountain effect snow. This type of snowfall occurs as winds push warm moist ground level moisture up mountain slopes to the upper atmosphere where the moisture is cooled and condensed and then falls back to earth settling on the mountains peak and surrounding areas. Now that it is understood how winter storms form we can discuss some other parameters of these storms. There are five types of precipitation associated with winter storms. Rain occurs in a winter storm as precipitation frozen in the upper atmosphere falls through a large band of above freezing temperatures and melts before reaching the warm earth and does not re freeze. Freezing rain occurs as precipitation frozen in the upper atmosphere falls through a smaller warm band of air in the mid level of atmosphere then enters a cold band along ground level and upon contact with cold surfaces refreezes and creates a sheet of ice. Sleet occurs as frozen precipitation in the upper atmosphere falls through a short warm band of air and then a large cold band of air refreezing into ice pellets before reaching earth. Hail is sleet of larger diameter that due to up drafting wind currents is circulated through the upper atmosphere several times combining with other freezing and thawing precipitation and increasing in size, hail stones are capable of reaching several inches in size. The final type of precipitation is snow which is

5 frozen in the upper atmosphere and falls though cold air to earth and does not melt. Snow storms are a specific type of winter precipitation that are separated into there own categories Winter snow storms are categorized based on several factors the amount of precipitation (accumulation), rate of precipitation, wind speed, and duration. There is no real system of separation only five general categories that snow storms are put into. Snow flurries are light snow falling for short durations with little or no accumulation or a light dusting expected. Snow Showers is snow falling at varying intensities for brief periods of time with some accumulation expected. Snow Squalls are brief intense snow showers accompanied by strong gusty winds, usually significant accumulation is expected, and squalls are often associated with lake effect snows seen in the great lakes region. Blowing Snow is wind driven snow that reduces visibility and causes significant drifting, this may also include loose snow that is already on the ground but is picked up and carried by the wind. Blowing snow is a significant problem across the flat virtually featureless landscapes of the Midwest where cars are often stranded in drifts along the highway. The final category of winter snow storm is the blizzard which is characterized by winds over 35 miles per hour and very heavy snowfall that reduces visibility to less than a quarter of a mile for a period of

6 at least three hours. These high winds and extreme cold temperatures are another interesting feature of winter storms. Winds are a factor in almost all winter storms and create some of the most dangerous conditions during the winter months. Winds combined with cold temperatures create a logarithmic condition called the wind chill in which the perceived temperature to humans is much colder than the actual ambient temperature. Exposure to cold and windy conditions can cause the onset of frostbite and hypothermia in minutes and also have severe effects on livestock and crops. Winter storms for and effect different regions of the country in different ways. There are five general regions that winter storms affect. The first region is from the Mid-Atlantic to New England Coastal region which are impacted by a specific type of winter storm called a Nor easter. This type of storm occurs as a low pressure system forms off of the Carolina coast and gains strength as it moves north. Strong wave action batters coastal areas and large amounts of moisture can combine with strong winds to create blizzard conditions and dump large amounts of snow throughout the northeast. The next region is compromised of the Gulf Coast and Southeast this region is especially sensitive to winter storms because of a

7 low awareness and preparedness level. Occasionally cold air sweeps this region and if precipitation occurs it tends to be wet snow or a freezing rain that ices this unprepared area of the U.S. The next region of interest is the Midwest and plains states. Winter storms that affect this area develop on the leeward side of the U.S. and Canadian Rockies, fueled by intense cold air from Canada these storms create blowing and drifting conditions along with extreme wind chill temperatures reaching seventy degrees below zero! The next region of concern compromises the area from the Rockies to the western coast of the U.S. In this area storms over the Pacific slam into the coast of Northern California Oregon and Washington with unlimited available moisture drawn from the Pacific pushing through the mountains and valleys with high winds and deep drifting snows. This region is also prone to avalanches due to steep mountain slopes and narrow passes that funnel winds creating damage to structures and closing roads. The Final Region Alaska is an entity in and of itself. This area of the U.S. is affected by storms that move across the bearing straight and intensify slamming the coast with intense wave action, ice flows and coastal flooding. The combination of heavy snows, very little sun light and extreme cold temperatures as low as ninety degrees below zero create massive accumulation and treacherous conditions for most of the winter months. As

8 you can see the vast majority of the United States is affected by winter storms but advance warning for many of these storms saves thousands of lives every year. There are several types of advance warnings that prepare citizens of the United States for forthcoming and potential hazardous winter storms. By listening for and understanding the different types of winter storm warnings available from radio and television news sources citizens can become better prepared and informed about winter s wrath. There are four basic preparedness warnings issued by the national weather service; these are outlooks, watches, warnings and advisories. An outlook is intended to inform people about possible winter storm conditions impending in the next 2-5 days. A winter storm watch tells the public that possible winter storm conditions are in the outlook for the next hours and now is the time to prepare. A winter storm advisory warns of winter weather conditions that are expected to cause significant inconveniences and may be hazardous, but using caution these storms should not be life threatening. A winter storm warning warns of life-threatening severe weather conditions that have begun or will begin within twenty four hours and demand action now. By listening to these warning and take some simple steps of precaution all but the most severe winter storms should not be life threatening to the average person.

9 There are several steps that the average person can take to prepare for the primary concerns during winter weather events. Being prepared for loss of a heating source, loss of power, loss of telephone service, and a shortage of food, water, medicine, and general supplies is the main concern during a winter storm. There are several websites ( that list items that should be kept on hand to prepare for winter weather as well as detailed emergency plans. The young and the old as well as pets and livestock are especially vulnerable to winter weather events and these websites also list detailed plans of action to deal with specific crisis and problems. The best plan to survive a winter storm or any similar environmental hazard is to stay alert informed and prepared prior to the weather event, by doing this most will survive this environmental hazard unscathed.