Blizzards, blowing snow in bitterly cold temperatures at wind speeds in excess of 35 mph , pound the Great Plains, northeastern United States, and southern Canada annually.  Defining a blizzard--as the National Weather Service does--as simply a strong winter storm with winds greater than 35 mph and visibility worse than ¼ mile for 3+ hours does^[1] not adequately highlight the destructive and paralytic nature of these storms.

Figure 1:  Picture of “white-out” blizzard conditions in Manitoba, Canada (courtesy of:  “Science program of Winnipeg School System:  http://www.wsd1.org/PC_Science/Weather/blizzard.htm)

It requires an in-depth analysis of weather conditions as well as geographical locations of these devastating winter storms to truly understand their full effect.  A common “partner-in-crime” of a blizzard is the cold wave—unusually cold air that travels southward to the middle and lower latitudes, dropping temperatures 20°F-30°F below average.  Several factors aid in the rapid transport of frigid air southward from arctic Canada and Siberia.  A ridge in the jet-stream often forms over western North America and a trough over the eastern half of North America. The ridge brings warm air northward over the west while the trough funnels cold air southward and to the east. In addition, the channeling effect of the Rocky Mountains forces cold air to follow a topographical path east of the mountain range, towards the central United States.^[2]  This bitterly cold air often contributes to the powerful blizzards that destroy agricultural systems, shut down interstate and intercity road systems, and trap people in their houses for days at a time.  A prime example of the destructive power of blizzards was seen in the north central U.S. in winter of 1996-1997.  This series of blizzards which pounded the Dakotas and Minnesota exacted a toll of $4.7 million in cattle loss, $6 million in farm property damage, and $21 million dollars in feed loss. (see Figure 2 for economic toll of winter storms)  Stockmen’s warnings are often issued for blizzards such as these that effect agricultural systems. These warnings are designed to inform and alert ranchers and farmers that a large amount of frozen precipitation, very cold temperatures and strong winds are forecasted for a given region.

Blizzards often decimate cattle population in the Great Plains (http://www.westford.com/fingerhut/Vermont/Frozen-Beef.jpg)

Most blizzards last for a day or less, however, it is possible for an area to experience a “cut off low,” or a storm that is “cut off” from the jet stream, causing it to hover over particular locations for upwards of a week. (Masters)^[3].  A blizzard truly begins to take shape when an eastward moving mid-latitude cyclone collides with an arctic front associated with a cold wave.  Once the two meet, the arctic front wraps around the cyclone’s center and becomes part of the cyclone’s structure.  As this “hybrid” system continues moving to the northeast, the pressure gradient intensifies, especially on the northwest side of the low-pressure system creating the powerful, frosty winds of the blizzard.  Blizzards can trek through several states leaving many inches of snow in their wake.  Whether pounding rural areas, or paralyzing intricate city systems the effects of blizzards are wide ranging. The staggering costs (see figure 2) stem from agricultural and livestock losses, car accidents, human death and  spikes in energy usage.  No matter the geographic location, these strong effects are always felt. 

Figure 2:  Annual cost of U.S. snowfall

(courtesy of Adams et. al 2004 and NOAA economics)

To piece together the ingredients of a blizzard, one must break down the weather conditions needed to meet criteria for a blizzard : falling or blowing snow, 35+ mph winds and reduced visibility for 3 or more hours. The cold air necessary for the formation of snow is often courtesy of a strong high pressure center created in Canada.  Air cooling in the lower troposphere aids in the formation of high pressure centers over the vast plains of central and northern Canada.  Long, calm, cloudless, polar nights help cool the surface by allowing infrared radiation to escape to space. During the heart of winter in Canada, nighttime lasts 18-20 hours in the northern latitudes. (to see that this is like, watch these videos taken at 70°N in winter )  As, the lower atmosphere is cooled, the surface pressure is increased due to the fact that cold air is more dense than warm air.  Once a cold, high-pressure center has formed, the calm and clear conditions which aided in its formation also help intensify the cold, before it begins its southward track into the northern parts of the United States.^[4]

The geography of North America aids in the formation of blizzards. As the cold air develops in the western plains of Canada, an Arctic Front often lurches southward bringing this bitterly cold air to the mid-latitudes.  When an extratropical cyclone forms east of the Rocky Mountains, snow typically falls to the north and west of the low-pressure system. The Arctic front and extratropical cyclone interact to the north of the low-pressure system, and the system moves to the northeast, it is intensified by strong pressure gradients which drive the cold air southward to the west of the center of the cyclone, thus creating the strong, cold winds of the blizzard.  As the cyclone progresses, warm air is forced upwards forming a clouds and precipitation.  Air continues to rise which condenses to form snow crystals which eventually fall to the ground. The heaviest snowfall amounts typically occur to the northwest of the low-pressure center in the wrap-around region of the extra-tropical cyclone. This weather pattern is highlighted in figures 1a and 2a.^[5]

 Another type of blizzard, know as a ground blizzard (illustrated in figure 3a) can be caused by cold winds whipping up dry, loose snow that was already on the ground.  Ground blizzards can occur on perfectly clear days, but can cause visibility that is as bad as or even worse than in a blizzard with snow that is falling.^[6]

Credit: Eric Snodgrass personal archive

Figure 1a

Credit: www.crh.noaa.gov/mkx/flyers/wntrmap.gif

Figure 2a

Credit: www.wrh.noaa.gov/images/pqr/blizzard.jpg

Figure 3a

The winter of 1996-1997 brought with it nine winter storms reaching blizzard criteria, millions of dollars in property/agricultural damage, and a huge spike in weather-related fatalities to North Dakota, South Dakota, and parts of Minnesota.  In January of 1997 in particular, 4 blizzards (an average of 1/week) paralyzed an already weather-stricken Northern Great Plains.  During that “Winter of Blizzards,” two presidential disaster warnings were issued—and for a good reason—the number of weather related fatalities spiked 19% higher than any other month in 1997 (courtesy of Weather.gov).  In giving a quick overview of weather conditions during this paralytic winter, during the 6 week, 6 blizzard stretch of time (15 December-24 January) there was one day with a high temperature above freezing.  In addition to these bitterly cold conditions, a total of 117 inches of snow blasted Fargo, ND maintaining an average depth of 22 inches! 

Economically, this winter exacted $21.5 million in agricultural damage (including the death of 10% of North Dakota’s entire cattle population).  Accenting these loses; 200,000 pounds of milk had to be discarded after their delivery was made impossible by the series of blizzards.  With weather fatalities spiking, paralytic blizzards hitting every week, and millions of dollars lost to the snow, North Dakota was soon impacted by a different (yet related) weather tragedy.

With greater than 100 inches of accumulated snowfall over a single winter, trouble was lurking down the road in the form of melting snow.  This threat was unleashed in late April when quick melting led the Red River to reach a record high crest of nearly 40 feet (see figure 1).  This flooding (which more than doubled the flood level of the river) decimated the Grand Forks and Fargo metro areas leaving thousands homeless and adding another layer of tragedy onto an already horrible winter.  This swift and devastating flood rose to submerge bridges, destroy countless homes and businesses and extend the paralytic state of the Northern Great Plains in late 1996 and early 1997. This immense flood was later dubbed, “The Flood of the Millennium” and stands as the greatest flood catastrophe on the Red River in recorded history.

REFERENCES

http://www.wrh.noaa.gov/fgz/science/blizzard.php?wfo=fgz

http://teacher.scholastic.com/activities/wwatch/winter_storms/experts.htm  (interview with Dr. Jeffery Masters, director of Meteorology for Weather Underground)

Severe and Hazardous Weather, Rauber, Walsh, Charlevoix  (2^nd edition)

http://www.wsd1.org/PC_Science/Weather/blizzard.htm   (figure 1)

http://www.economics.noaa.gov/?goal=weather&file=events/snow   (figure 2)