Halloween Blizzard

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Halloween Blizzard

The "Halloween Blizzard" winds up over the Central U.S.
Storm type:	Cyclonic blizzard, Gulf Low
Formed:	October 31, 1991
Dissipated:	November 3, 1991
Maximum amount1:	37 inches (94 cm) (Duluth, MN)
Lowest pressure:	984 mbar (hPa)
Damages:	$100 Million (2005 USD)
Fatalities:	22
Areas affected:	Eastern and southern Minnesota, northwestern Wisconsin, central Iowa
1Maximum snowfall or ice accretion

The Halloween Blizzard was a period of heavy snowfall and ice accumulation that affected parts of the Upper Midwest of the United States, from October 31–November 3, 1991. Over the last week of October, 1991 a large storm system over the Atlantic Ocean (1991 Halloween Nor'easter) blocked most of the weather patterns over the eastern half of the United States, and in turn moisture from the Gulf of Mexico was funneled straight northward over the affected region. By the time the precipitation stopped falling many cities in the eastern half of Minnesota and northwestern Wisconsin would witness record early-season snowfall accumulations, while parts of southern Minnesota and northern Iowa were crippled by a large ice storm. Arctic air that was pulled southward behind the storm would combine with the heavy snow pack to produce many record low temperatures. Between the blizzard and the ice storm 22 people were killed and over 100 were injured.^[1]

[edit] Meteorological synopsis

The meteorological circumstances surrounding the formation of the Halloween Blizzard are unique. During the final week of October 1991, a large cutoff extratropical storm system, dubbed "The Perfect Storm", began intensifying over the Atlantic Ocean off the east coast of the United States and Canada. Behind it, a large ridge of high pressure extended from Greenland to the Southeast United States. Meanwhile, another area of low pressure in Nebraska was being pushed northward, up the west side of the high pressure ridge towards Hudson Bay. Behind that area of low pressure was a strong cold front. By October 30, that cold front stretched from the Hudson Bay to the Gulf of Mexico. Many areas in the northern plains of the United States had dropped below freezing, so the cold air necessary to produce snow was in place. Also at this time, the storm was nearing peak intensity and began to move back to the west, opposite the normal flow of mid latitude cyclones in the northern hemisphere. The caused the cold front over the Midwest to stall and become stationary.

Surface map from October 30, 1991. The "Perfect Storm" is on the right hand side of the map, the ridge of high pressure sits over the eastern U.S. and a cold front cuts through the center of the country.

By October 30, the conditions were favorable to allow a Gulf Low to form. A Gulf Low is an area of low pressure that develops or strengthens over or near the Gulf of Mexico, often after a strong cold front has pushed through the central United States. Because Gulf Lows form near the moisture-rich Gulf of Mexico, the two ingredients needed for snow (moisture and below freezing temperatures) are often both present. Along with Nor'easters, Gulf Lows are generally the most potent snowfall producing storms in the eastern United States.

A large outbreak of cold air had taken over the central United States, with the trailing edge of the cold front sitting near Houston, Texas. It was here that the area of low pressure formed and on October 31 began to rapidly intensify. Normally storm systems that form in this region will be driven northeastward by the jet stream towards the central Great Lake states, or perhaps eastward towards the Southeast U.S.^[2] However, because the massive storm was pushing back towards the United States, the normal west to east storm track in the eastern United States was essentially blocked. The clockwise wind direction around the ridge of high pressure over the eastern United States pulled the Gulf Low almost straight to the north. The low would move from Houston, Texas on October 31 to Thunder Bay, Ontario on November 2, which is approximately 1400 mi (2,200 km) to the north and just 350 mi (550 km) east.^[3]

Because of the prevailing westerly winds in the mid-latitudes of the northern hemisphere, it is very unusual for a storm system to travel that that far north or south without getting pushed further to the east by generally west to east moving jet stream winds.^[4] In turn, places like Iowa, Minnesota and western Wisconsin would be affected by the Gulf Low. These are places that do not experience this type of storm track very often.^[5] As the low pressure area pulled to the north, copious amounts of moisture traveled with it. The moisture combined with the cold air already in place to produce large amounts of precipitation, mostly in the form of freezing rain and heavy snow.

[edit] Precipitation

Snowfall totals for the Halloween Blizzard

The precipitation from this system began falling as snow in Iowa late on October 30, and by the morning of October 31 it had changed over to ice and spread northward across southeast Minnesota. During Halloween day the precipitation spread to the north where it fell mostly as rapidly accumulating snow. The snow continued to develop northward, eventually spreading into the Minnesota Arrowhead. Eventually all of the precipitation changed over to snow, and in some areas it would continue falling until November 3.

[edit] Snow

The heavy snow began falling across east central Minnesota and northwest Wisconsin during the late afternoon hours of October 31. By midnight, the Twin Cities had already recorded 8.2 in (20.8 cm) of snow. This not only set a record for the most amount of snow on that date, but also for the most snow ever recorded in the Twin Cities during the month of October. As the storm system pushed its way northward, more communities in eastern Minnesota and northwestern Wisconsin began to experience similar conditions.

Over the next two days the snow continued to fall, leading to additional snowfall of one to two feet (30 cm to 60 cm). By the time the snow ended on November 3 the storm had dropped 36.9 in (93.7 cm) on Duluth, the largest single snow storm total in Minnesota history at that time. The Twin Cities received 28.4 in (72.1 cm), setting a single storm record for the metropolitan area. In all, at least one foot (30 cm) of snow fell in a swath approximately 100 mi (160 km) wide from south central Minnesota, northeastward into northwestern Wisconsin and into the Minnesota Arrowhead. A more narrow band of 2+ ft (60+ cm) of snow fell from the Twin Cities to Duluth and northward.

[edit] Ice

Areas of southern Minnesota and Iowa along and south of the I-90 corridor did not see as much snow, but instead saw a major ice storm. Though the precipitation started out as snow in these areas, it changed over to ice during the day on October 31 continued falling over the next day. Ice accumulations as high as 2–3 in (6 cm–9 cm) were recorded in these areas before the precipitation changed to snow. Up to 10 in (25.4 cm) of snow proceeded to fall on top of ice accumulations from the previous day, making travel even more treacherous.^[6] Up to 1 inch of ice accumulation was reported as far south as Omaha, Nebraska.^[7]

[edit] Impact

Most of Minnesota, western Wisconsin and northern Iowa were heavily impacted by the storm. $63+ million in damages was reported from fallen power lines, and $5 million in crop damages were reported in Iowa. Eleven counties in southern Minnesota were declared federal disaster areas, and 52 counties in Iowa were declared disaster areas. At least 100,000 people lost power because of the weight of the ice downing power lines, and in some cases it took up to a week for the power to be restored.

Many roads were closed both from the snow and ice, including long stretches of I-90, I-35 and I-29 in Iowa, Minnesota and South Dakota.^[8] Highway snow removal was hindered by record cold temperatures that followed the storm and transportation was hampered for many days.^[9] Twenty two people died in this storm, twenty in Minnesota and two on the Mississippi River near La Crosse.

[edit] Records

In eastern Minnesota, the Halloween Blizzard shattered many of the previous October snowfall records. The 8.2 inches that fell in the Twin Cities on October 31 was more snow than had ever been recorded in any October in its recorded history. November 1 saw similar daily records fall, but with a more wide reaching area from most of central Minnesota eastward to La Crosse and Eau Claire, Wisconsin. Following the storm Arctic air poured southward from Canada to produce many record low temperatures in these same areas. Bismarck, North Dakota, sank to -10 F on October 31, breaking their previous record low of 6 F by 16 degrees.^[10] Record snow and cold was recorded as far south as Nebraska and Colorado.^[11][12] The Arctic air also spread over Chicago, recording a low of 11 on November 4.^{[13] [14]}

Four weeks later on November 29–30, another large storm system dropped as much as 18 inches of snow over these same areas. These two storms combined to set a single-month record for most snowfall in the Twin Cities and Duluth.

[edit] See also

• The Perfect Storm
• Climate of Minnesota
• List of Minnesota weather records

[edit] Notes and references

[edit] External links

• Minnesota Public Radio - Jet Streaming for Wednesday, October 31, 2007 (MP3)