Climate of Minnesota
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The Climate of Minnesota is typical of a continental climate with cold winters and hot summers. Its location in the Upper Midwest allows it to experience some of the widest variety of weather in the United States, and each of the four seasons has its own distinct characteristics. The areas near Lake Superior in the Minnesota Arrowhead region experience weather unique from the rest of the state. The moderating effect of Lake Superior keeps the surrounding area relatively cooler in the summer and relatively warmer in the winter, giving that region a taste of a maritime climate. On the Koppen climate classification, the southern half of Minnesota, roughly from the Twin Cities region southward, falls in the hot summer humid continental climate zone (Dfa), and the northern two-thirds of Minnesota falls in the warm summer humid continental climate zone (Dfb).
Winter in Minnesota is characterized by cold (below freezing) temperatures and snowfall. Snow is the main form of winter precipitation, but freezing rain, ice, sleet and sometimes even rain are all possible during the winter months. Common storm systems include Alberta Clippers or Panhandle hooks, some of which evolve into blizzards. Annual snowfall extremes have ranged from over 170 in (432 cm) in the rugged Superior Highlands of the North Shore to as little as 10 in (25 cm) in southern Minnesota. Temperatures as low as −60 °Fahrenheit (−51 °C) have occurred during Minnesota winters. Spring is a time of major transition in Minnesota. Early spring commonly sees snowstorms, but by late spring as temperatures begin to moderate the state can experience tornado outbreaks, a risk which lasts through the summer into the fall.
Summer sees heat and humidity predominate in the south, while warm and less humid conditions are generally present in the north. These humid conditions help kick off thunderstorm activity 30–40 days a year. Summer high temperatures in Minnesota average in the mid 80's (30 °C) in the south to the upper 70's (25 °C) in the north, with temperatures as hot as 114 °F (45.5 °C) possible. The growing season in Minnesota varies from 90 days per year in the Iron Range to 160 days in southeast Minnesota. Tornadoes are possible in Minnesota from March – November, but the peak tornado month is June, followed by July, May, and August. The state averages 24 tornadoes per year. Minnesota is the driest state in the Midwest. Average annual precipitation across the state ranges from around 35 in (89 cm) in the southeast to just 20 in (51 cm) in the northwest. Autumn weather in Minnesota is largely the reverse of spring weather. The jet stream, which tends to weaken in summer, begins to re-strengthen, leading to a quicker changing of weather patterns and an increased variability of temperatures. By late October and November these storm systems become strong enough to form major winter storms. Fall and spring are the windiest times of the year in Minnesota.
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[edit] General climatology
Due to its location in the center of North America Minnesota experiences temperature extremes characteristic of a continental climate, with cold winters and mild to hot summers in the south and frigid winters and generally cool summers in the north.<ref>NCRFC Climate and Topography. National Oceanic & Atmospheric Administration. Retrieved on 2006-11-10.</ref> Each season has distinctive upper air patterns which bring different weather conditions with them. Another feature of a continental climate is that weather patterns can be unpredictable. For example, an Alberta clipper, a low pressure system originating in the province of Alberta in Canada, would be a common winter occurrence in Minnesota. But with the general unpredictability of weather in a continental climate, such a storm system could occur in spring, or in late autumn.<ref> What is an "Alberta Clipper"?. Yahoo!. Retrieved on 2006-11-10. </ref> Hot weather, though usually confined to June, July, and August, can sometimes begin as early as April or May, and could spill over into September.<ref> Mid-April Heat Wave. Minnesota Climatology Office (2002-04-15). Retrieved on 2006-11-10. </ref>
Being 1,000 miles (1,600 km) from any large body of water (with the exception of Lake Superior), temperatures and precipitation in Minnesota can vary widely. Minnesota is far enough north to experience −60 °Fahrenheit (−51 °C) temperatures and blizzards during the winter months, but far enough south to experience 114 °F (45.5 °C) temperatures and tornado outbreaks in the summer.<ref> Minnesota Climate Facts. Minnesota DNR (2004). Retrieved on 2006-11-10. </ref> The 174 degree (96 °C) variation between Minnesota's highest and lowest temperate is the 11th largest variation of any U.S. State, and 3rd largest of any non-mountainous state (behind North Dakota and South Dakota).<ref> U.S. Extreme Record Temps & Differences. Golden Gate Weather Services (2005). Retrieved on 2006-11-23. </ref>
| Average Temperatures in Minnesota (in °Fahrenheit)<ref name="normals"> Ross, Douglas. U.S. Climate Normals. National Oceanic & Atmospheric Administration. Retrieved on 2006-11-10. </ref> | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sept | Oct | Nov | Dec | |
| Alexandria | 8 | 15 | 27 | 43 | 56 | 65 | 70 | 68 | 58 | 45 | 28 | 14 |
| Duluth | 8 | 15 | 25 | 39 | 52 | 60 | 66 | 64 | 55 | 44 | 28 | 14 |
| International Falls | 3 | 11 | 24 | 39 | 53 | 62 | 66 | 64 | 53 | 42 | 24 | 9 |
| Rochester | 12 | 18 | 31 | 45 | 57 | 66 | 70 | 68 | 59 | 47 | 31 | 17 |
| Twin Cities | 13 | 20 | 32 | 47 | 59 | 68 | 73 | 71 | 61 | 49 | 32 | 19 |
| Worthington | 11 | 18 | 29 | 44 | 57 | 67 | 71 | 68 | 59 | 47 | 30 | 17 |
| Average Temperatures in Minnesota (in °Celsius)<ref name = normals /> | ||||||||||||
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sept | Oct | Nov | Dec | |
| Alexandria | -13 | -9 | -3 | 6 | 13 | 18 | 21 | 20 | 14 | 7 | -2 | -10 |
| Duluth | -13 | -9 | -4 | 4 | 11 | 16 | 19 | 18 | 13 | 7 | -2 | -10 |
| International Falls | -16 | -12 | -4 | 4 | 12 | 17 | 19 | 18 | 12 | 6 | -4 | -13 |
| Rochester | -11 | -8 | -1 | 7 | 14 | 19 | 21 | 20 | 15 | 8 | -1 | -8 |
| Twin Cities | -11 | -7 | 0 | 8 | 15 | 20 | 23 | 22 | 16 | 9 | 0 | -7 |
| Worthington | -12 | -8 | -2 | 7 | 14 | 19 | 22 | 20 | 15 | 8 | -1 | -8 |
Minnesota is far from major sources of moisture and is in the transition zone between the moist East and the arid Great Plains. Annual average precipitation across the state ranges from around 35 in (89 cm) in the southeast to just 20 in (51 cm) in the northwest.<ref> Daly, Christopher (1990). Annual Average Precipitation (JPG). Desert Research Institute. Retrieved on 2006-11-10. </ref> Snow is the main form of precipitation from November through March, while rain is the most common the rest of the year. Annual snowfall extremes have ranged from over 170 in (432 cm) in the rugged Superior Highlands of the North Shore to as little as 10 in (25 cm) in southern Minnesota.<ref name="extremes"> Climate Extremes for Minnesota. Minnesota Climatology Office (2004-09-08). Retrieved on 2006-11-10. </ref> It has snowed in Minnesota during every month with the exception of July, and the state averages 110 days a year with snow cover of greater than an inch (2.5 cm). <ref name=almanac>Seely, Mark (2006). Minnesota Weather Almanac. Minnesota Historical Society press. ISBN 0873515544.</ref>
[edit] Lake Superior
The areas near Lake Superior in the Minnesota Arrowhead region experience unique weather in the state. The moderating effect of Lake Superior keeps the surrounding area relatively cooler in the summer and relatively warmer in the winter, giving those areas a taste of a maritime climate. Even though Lake Superior has a large impact on the local climate near the shore, the impact does not stretch very far. Just a few miles inland from Lake Superior are the Sawtooth Mountains. This elevated area of land largely keeps the moderate marine air masses and associated precipitation close to the shoreline.<ref> Snowfall, 2005-11 - 2006-04. Minnesota Climatology Office (2006). Retrieved on 2006-11-10. </ref> Grand Marais for example, which is on the shore of Lake Superior, has an average July high temperature of 70 ° F (21 ° C). 100 miles to the west in Virginia, the average July high temperature is 77 ° F (25 ° C). Conversely, Virginia's average high temperature in January is 15 ° F (−9 ° C), while Grand Marais is a relatively balmy 23 ° F (−5 ° C).<ref> Average climate in Minnesota. citydata.com. Retrieved on 2006-11-10. </ref> The climatalogical effects of Lake Superior tend to stifle convection, thus limiting the potential for tornadoes.<ref name=almanac /> Even though Cook and Lake counties are two of the largest counties in the state, the two have combined to produce just 7 tornadoes in the past 56 years.<ref> Minnesota Tornadoes by County 1950 - 2005 (JPG). National Oceanic & Atmospheric Administration (2005). Retrieved on 2006-11-26. </ref>
Places near the shoreline also can receive lake effect snow, but because the state lies on the north side of Lake Superior the snowfall amounts aren't nearly as large as they are as towns in Wisconsin and Michigan that lie to the south of the lake.<ref> Analysis of Snow Climatology. Minnesota Climatology Office. Retrieved on 2006-11-21. </ref><ref> 2004 - 2005 Season Snowfall Totals (JPG). National Oceanic & Atmospheric Administration. Retrieved on 2006-11-21.</ref> Big lake effect snows are still possible though, as the single largest snowstorm in Minnesota history was a lake effect event. On January 6, 1994 Finland received 36 in (91 cm) of lake effect snow in 24 hours, and 47 in (119 cm) over a three day period. Both are Minnesota records. At 85 in (216 cm) per year, the port city of Duluth has the highest average snowfall total of any city in Minnesota.<ref> Climate Summaries. University of Illinois. Retrieved on 2006-11-10. </ref>
[edit] Winter
Even though winter doesn't officially start until late December, Minnesota usually begins experiencing winter-like conditions in November, sometimes as early as late October. As with many other Midwestern cities, winter in Minnesota is characterized by cold (below freezing) temperatures and snowfall. Weather systems can move in from the north, west, or south, with the majority of the weather being driven in from the north. A vigorous jet stream brings high and low-pressure systems through in quick succession, which can cause large temperature variations over a short period of time.
[edit] Temperature
As the last remnants of summertime air in the southern U.S. start to lose their grip, cold polar air building up in northern Canada starts to push farther and farther south, eventually spreading into Minnesota. By the time December and January arrive, Minnesota is fully engulfed in the polar air and is then subjected to arctic air masses moving in. Because there are no natural barriers north or northwest of Minnesota to block arctic air from pouring south, Minnesota gets regular shots of the arctic air through the winter.<ref name="mnclimate"> Climate of Minnesota (PDF). National Climatic Data Center. Retrieved on 2006-11-10. </ref> High pressure systems which descend south from the Canadian plains behind the fronts bring light winds, clear skies, and bitterly cold temperatures. The northern part of Minnesota gets the brunt of the cold air with temperatures commonly reaching −30 ° F (−34 ° C). On average, Tower, Minnesota, sometimes called the "Icebox of the nation", sinks below zero (−17 ° C) 71 times per year.<ref> Potter, Sean (2006-8-10). Icebox of the Nation. USA Today. Retrieved on 2006-11-10. </ref> The air mass then slowly moderates as it moves south into the rest of the state. Alberta clippers alternate with these high-pressure systems, bringing slightly warmer temperatures and fairly regular snowfall with them.
Minnesota occasionally gets breaks from the polar and arctic air when a zonal flow takes hold. This means that the jet stream will move in a west to east motion (rather than north to south) and push air from the Pacific Ocean into the region. In Minnesota this pattern commonly leads to a prolonged period of above freezing high temperatures that gives Minnesotans a break from the winter freeze. Storms that move into Minnesota from a more westerly direction generally do not bring significant amounts of precipitation with them.<ref> Gianassca, Frank. Zonal winds tend to bring calm weather. USA Today. Retrieved on 2006-12-03. </ref>
[edit] Precipitation
Winter precipitation comes in a few different forms. Snow is the main form of precipitation, but freezing rain, ice, sleet and sometimes even rain are all possible during the winter months. Larger storm systems, often Panhandle hooks or other storms originating from the Pacific Ocean, can bring large amounts of snow and even blizzard conditions.
[edit] Alberta Clippers
Alberta Clippers are usually the storms responsible for ushering arctic air into Minnesota.<ref> Palmer, Chad. Alberta Clippers reinforce cold air. USA Today. Retrieved on 2006-11-15. </ref> As their name suggests, they form in and near Alberta, Canada. Other variations of the same kind of system are Manitoba Maulers or Saskatchewan Screamers, the name simply depends on where the storms form. Like Minnesota, Alberta is blocked from a major moisture source, so Clippers usually have very limited moisture available to them. Rarely do they produce more than 6 in (15 cm) of snow, although it is possible to receive up to a foot (30 cm) or more if enough moisture can work its way into the system.<ref> Henson, Bob. Alberta Clipper. The Weather Notebook. Retrieved on 2006-11-10. </ref> The big story with Alberta Clippers is what comes in behind them, and that is arctic air and dangerous wind chills. Because the air associated with a clipper is usually very cold, the snow that does fall has a very low moisture content and is of the 'fluffy' variety. Alberta Clippers often proceed to become copious lake effect snow producers on the southern shores of the great lakes.<ref> Lake Effect Snow. The Weather Channel. </ref>
[edit] Panhandle Hooks
In terms of their characteristics, panhandle hooks are nearly the opposite of Alberta clippers. Instead of forming in the north and dropping south, these form in the southwestern United States and then move northeast. They get their name from the location where they usually make their turn to the north; near the panhandles of Oklahoma and Texas. Unlike clippers, these storms usually have a great deal of moisture to work with. As the storms make their turn to the north, they pull in moist air from the nearby Gulf of Mexico and bring it northward with them toward Minnesota or other parts of the Midwest.<ref> Panhandle Hook. National Oceanic and Atmospheric Administration. Retrieved on 2006-11-15. </ref> Another effect of Panhandle hooks is that they usually bring a substantial amount of warmer air northward with them. As these systems move to the northeast, there will usually be a heavy band of snow to the northwest of the low pressure center if there is enough cold air present.<ref> Texas Hooker. National Oceanic and Atmospheric Administration. Retrieved on 2006-12-03. </ref> A wintery mix of precipitation, rain, or sometimes even thunderstorms will then often occur to the south of it.<ref> Panhandle Hook. National Oceanic and Atmospheric Administration. Retrieved on 2006-12-03. </ref> Snowfall over a foot (30 cm) is not uncommon with a panhandle hook, and because of the high moisture content in these systems the snow is usually very wet and heavy. Large panhandle hooks can become powerful enough to draw in arctic air after they pass by the state, leaving bitter cold temperatures and wind chills in their wake. Panhandle Hooks are responsible for some of the most famous blizzards that have occurred in the Midwest.
[edit] Spring
Spring is a time of major transition in Minnesota. As winter nears its end, the sun rises higher in the sky and temperatures begin to moderate. As this happens much of the Midwest starts to experience severe thunderstorms and tornadoes. Storm systems that move inland from the Pacific begin to collide with the increasingly warm and moist air from the Gulf of Mexico. In the early part of the spring Minnesota is usually located too far to the north to experience severe weather, as the warm air needed for it simply has not yet pushed that far to the north.<ref name="tornadoes"> Minnesota Tornado History and Statistics. Minnesota Climatology Office (2006-09-20). Retrieved on 2006-11-10. </ref> Early spring tornado outbreaks do occur occasionally in Minnesota though, as evidence by the Comfrey - St. Peter Tornado Outbreak on March 29, 1998. More often, Minnesota is on the northern (cooler) side of major storm systems in the early spring, which instead results in rain, and if it's cold enough, snow. Even though the winter snow pack starts to melt in southern Minnesota during mid-March, there is still enough cold air available in Canada to produce major snow storms into late April.<ref> April Fool's Day Snowfall of 2002. Minnesota Climatology Office (2002-04-02). Retrieved on 2006-11-10. </ref>
As spring goes on, the storm systems start to push farther and farther to north, and southern Minnesota becomes more prone to severe thunderstorms and tornadoes.<ref name = tornadoes /> As spring moves into the later stages, the chances for snow continue to drop and eventually disappear, south to north. By the time it gets warm enough for severe weather in northern Minnesota, the strength of storm systems have usually started to decrease, which results in fewer severe storms in northern Minnesota compared to the southern part of the state.
| Average Precipitation in Minnesota (in inches) <ref name = normals /> | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sept | Oct | Nov | Dec | |
| Alexandria | 1.0 | 0.7 | 1.5 | 1.9 | 3.0 | 4.4 | 3.3 | 3.6 | 2.7 | 2.2 | 1.2 | 0.6 |
| Duluth | 1.1 | 0.8 | 1.7 | 2.1 | 3.0 | 4.3 | 4.2 | 4.2 | 4.1 | 2.5 | 2.1 | 0.9 |
| International Falls | 0.8 | 0.6 | 1.0 | 1.4 | 2.6 | 4.0 | 3.4 | 3.1 | 3.0 | 2.0 | 1.4 | 0.7 |
| Rochester | 0.9 | 0.8 | 1.9 | 3.0 | 3.5 | 4.0 | 4.6 | 4.3 | 3.1 | 2.2 | 2.0 | 1.0 |
| Twin Cities | 1.0 | 0.8 | 1.9 | 2.3 | 3.2 | 4.3 | 4.1 | 4.1 | 2.7 | 2.1 | 1.9 | 1.0 |
| Worthington | 0.7 | 0.6 | 1.9 | 2.7 | 3.4 | 4.6 | 3.6 | 3.5 | 2.6 | 2.0 | 1.7 | 0.7 |
| Average Precipitation in Minnesota (in centimeters) <ref name = normals /> | ||||||||||||
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sept | Oct | Nov | Dec | |
| Alexandria | 2.5 | 1.8 | 3.8 | 4.8 | 7.6 | 11.2 | 8.4 | 9.1 | 6.9 | 5.6 | 3.0 | 1.5 |
| Duluth | 2.8 | 2.0 | 4.3 | 5.3 | 7.6 | 12.3 | 11.8 | 11.8 | 10.4 | 6.4 | 5.3 | 2.3 |
| International Falls | 2.0 | 1.5 | 2.5 | 3.6 | 6.6 | 10.2 | 8.6 | 7.9 | 7.6 | 5.1 | 3.6 | 1.8 |
| Rochester | 2.3 | 2.0 | 4.8 | 7.6 | 8.9 | 10.2 | 4.6 | 12.3 | 7.9 | 5.6 | 5.1 | 2.5 |
| Twin Cities | 2.5 | 2.0 | 4.8 | 5.8 | 8.1 | 12.3 | 10.4 | 10.4 | 6.9 | 5.3 | 4.8 | 2.5 |
| Worthington | 1.8 | 1.5 | 4.8 | 6.9 | 8.6 | 11.7 | 9.1 | 8.9 | 6.6 | 5.1 | 4.3 | 1.8 |
[edit] Wind
With the exception of areas along the shores of Lake Superior, winds in Minnesota generally prevail from the north and northwest in the winter, and south and southeast in the summer.<ref name=almanac /> On average, fall and spring are the windiest times of the year in Minnesota. October is the windiest month in northwest Minnesota, while April is the windiest over the rest of the state.<ref> Minnesota has more potential for wind energy. Rochester Post Bulliten (2006-02-08). Retrieved on 2006-11-10. </ref> Winds generally average between 9 and 11 miles per hour (14 – 18 km/h) across the state, with one major exception. The heaviest winds in the state are found on the Buffalo Ridge, or Coteau des Prairies, a flatiron-shaped area extending from Watertown, South Dakota, diagonally across southwestern Minnesota and into Iowa. Created by two lobes of a glacier parting around a pre-existing plateau during the (Pleistocene) Ice Age, the Buffalo Ridge is ideal for wind power generation, with average wind speeds of 16.1 miles per hour (26.8 km/h).<ref>Buffalo Ridge Wind Power Plant. Xcel Energy. Retrieved on 2006-11-02.</ref>
[edit] Floods
Minnesota is prone to flooding in its major rivers, most of the time due to spring snowmelt runoff. Spring flooding to some degree occurs almost annually on some Minnesota rivers, but major flooding has occurred in 2001, 1997, 1993 1969 and 1965.<ref> Flood Information. Army Corps of Engineers. Retrieved on 2006-11-24. </ref> Unlike the other four, the 1993 flooding was mainly due to heavy late-spring and summer rains.<ref> Larson, Lee (1996-06-28). The Great USA Flood of 1993. National Oceanic and Atmospheric Administration. Retrieved on 2006-11-24. </ref> The flooding in 1965 was the worst flood in Minnesota history on the Mississippi River, while the flooding in 1997 was the worst in history on the Red River.<ref> The Mississippi River Flood of 1965. National Oceanic and Atmospheric Administration (2005-11-08). Retrieved on 2006-11-18. </ref> The Red River flood of 1997 was aided heavily by the 11 blizzards that struck Minnesota (many of which affected the northwest part of the state) that winter.<ref name=almanac /><ref> Famous Minnesota Winter Storms. Minnesota Climatology Office (2001-12-10). Retrieved on 2006-11-24. </ref> Besides heavy winter and spring snowfall, cold winter temperatures and heavy fall and spring rains are also common causes of river flooding in Minnesota. <ref> Climatic Conditions Leading to the Spring Flooding of 2001. Minnesota Climatology Office (2001-04-21). Retrieved on 2006-11-24. </ref>
[edit] Summer
During a Minnesota summer, heat and humidity predominate in the south, while warm and less humid conditions are generally present in the north. A main feature of summer weather in Minnesota and the Midwestern United States as a whole is the weakening of the jet stream, leading to slower movement of air masses, a general increase in the stability of temperatures, and less wind.<ref> Typical speeds of jet stream winds. USA Today (2003-12-03). Retrieved on 2006-11-10. </ref> The strong wind that does blow almost always comes from the south, bringing warm and humid temperatures with it. These humid conditions and a jet stream that has pushed into the northern parts of the U.S. help kick off thunderstorm activity 30–40 days a year.<ref> U.S. Thunderstorm Distribution. National Oceanic and Atmospheric Administration. Retrieved on 2006-10-25. </ref>
[edit] Temperatures
Daily average summer temperatures in Minnesota range from the low 70's (22 °C) in the south to the mid 60's °F (19 °C) in the north.<ref name = normals /> Because summer time air masses are not as volatile as in the winter, daily high and low temperatures rarely vary more than 15 degrees (7 °C) either side of normal. While summertime around much of the country means long stretches of hot and humid weather, Minnesota is located far enough north where cooler, drier shots of air frequently move in behind cold fronts dropping south from Canada. The cooler air typically does not stick around very long though, and is quickly replaced by the warmer and more humid gulf air once again. The drier air moving into hot and humid summertime air keep the threat of thunderstorms and tornadoes around in Minnesota through July and August.<ref name = tornadoes /> Northern Minnesota is considerably cooler and less humid than southern Minnesota is during the summer months. For example, Duluth's annual average temperature and dew point are 6 degrees (3.4 °C) cooler than in Minneapolis.<ref> Air Temperatures & Dew Points – Great Lakes States. Minnesotans For Sustainability. Retrieved on 2006-11-10. </ref>
July is the hottest month in Minnesota state-wide, and is usually the month when the worst heat waves occur. In July 1936 Minnesota and the rest of the Midwest suffered through its worst heat wave on record. Most of the state was engulfed in 100 °F (38 °C) temperatures for several days in a row, and Minnesota's all time record high temperature of 114 °F (46 °C) was set during this stretch. This heat wave was also responsible for breaking the Twin Cities all time record high of 108 °F (42 °C), as well as the all time record high of several other cities across the state.<ref> Tuesday, July 7, 1936: How to keep cool. Minneapolis Star Tribune. Retrieved on 2006-11-10. </ref>
[edit] Precipitation
The summer months of June, July and August account for around half of the annual precipitation total across the state of Minnesota.<ref> Normal Precipitation Maps. Minnesota Climatology Office (2003-11-13). Retrieved on 2006-11-10. </ref> Most of this rain falls from thunderstorms, a frequent summer occurrence. Even though summer is the primary season for Minnesota to experience thunderstorms, they can occur from March to November. These storms can and do become severe, producing large hail, strong winds, and tornadoes. Minnesota has experienced several major derecho events, most recently the Boundary Waters-Canadian Derecho which blew down millions of trees in the Boundary Waters Canoe Area Wilderness (BWCA) on July 4 1999.<ref> The Boundary Waters-Canadian Derecho. National Oceanic and Atmospheric Administration. Retrieved on 2006-12-03. </ref> In addition to derechos, strong tornadoes also occur from severe thunderstorms.
Summertime thunderstorms are fueled by dew points that often reach into the 70's ° F (21 ° C) and sometimes even 80 ° F (27 ° C).<ref> High Dew Point Temperatures. Minnesota Climatology Office (2005-07-28). </ref> In addition to severe conditions, thunderstorms produce heavy rain and cloud to ground lightning. Heavy rain brings flash floods to Minnesota three days per year.<ref name = mnclimate /> With the exception of hail, summer precipitation in Minnesota is almost always in the form of rain. The lone exception is in far northern Minnesota, when in mid-September the chances for small amounts of snow become a possibility.<ref> September in the Northern Plains. Intellicast.com. Retrieved on 2006-11-22. </ref>[edit] Droughts
As with any agricultral state droughts are an annual summer concern in Minnesota, especially for farmers. The growing season (which varies from 90 days per year in the Iron Range to 160 days in southeast Minnesota) is when Minnesota averages its highest percentage of annual precipitation, so a lack of rainfall during this time period can be devastating to crops.<ref name = mnclimate /> The last major drought in Minnesota was in 1988. During that year the period of April – July of that year was the 2nd driest in the previous century, and the period of May – August was the hottest on record. The combination of dry skies and heat caused a severe drought which cost the state approximately 1.2 billion dollars in crop losses.<ref> Drought of 1988 (PDF). Minnesota DNR (1989-01). Retrieved on 2006-11-21. </ref> Other memorable drought years were 1976 and the Dust Bowl years of the 1930's. During the dust bowl years inappropriate farming techniques, enhanced by years of drought conditions led to dust storms in Minnesota and the other parts of the Midwest.<ref> Timeline of the Dust Bowl. PBS. Retrieved on 2006-11-26. </ref> Drought conditions also have helped spawn forest fires. In 1894 the Great Hinckley Fire destroyed Hinkley killing up to 459 people, and in 1918 a forest fire killed 453 people in and around Cloquet.<ref> Monday, Oct. 14, 1918: Hundreds die in Cloquet fire. Minneapolis Star Tribune (2005-11-11). Retrieved on 2006-11-26. </ref> More recently, in 2006, the Cavity Lake Fire burned 31,830 acres in the BWCA.<ref> Cavity Lake fire nearly history. Associated Press (2006-08-06). Retrieved on 2006-11-26. </ref> This location still lays host to millions of dead trees, blown over during the derecho event in 1999.
[edit] Tornadoes
Tornadoes are possible in Minnesota from March – November, but the peak tornado month is June, followed by July, May, and August. Tornadoes are most common in the southern part of the state, which is located on the northern edge of tornado alley. Even though Minnesota does not receive as many tornadoes as other parts of the Midwest, Minnesota has seen its share of deadly storms. The state averages 24 tornadoes per year,<ref name = tornadoes /> and on average has an F5 tornado once every 25 years. Some of the memorable Minnesota tornadoes and outbreaks are:- August 21, 1883: An F5 tornado struck Rochester, Minnesota killing 37. This tornado led to the construction of a new hospital, which eventually evolved into the Mayo Clinic.
- April 14, 1886: A large tornado struck Sauk Rapids, Minnesota killing 72. This was Minnesota's deadliest tornado on record.<ref> Sauk Rapids History. City of Sauk Rapids. Retrieved on 2006-11-10. </ref>
- May 6, 1965: Four F4 tornadoes ripped through the Twin Cities metro area (two of them in Fridley), killing 13.
- July 18, 1986: KARE 11 broadcast a tornado in Fridley from a news helicopter live on their 5:00 PM news.<ref> Costantini, Allen (2006-07-19). Tornado's 20th Anniversary, an event to remember. KARE 11. Retrieved on 2006-11-15. </ref>
- June 16, 1992: Minnesota experienced its busiest tornado day ever with 27 recorded twisters. The largest tornado in this family was an F5 that struck Chandler, Minnesota, killing one. This is the most recent F5 tornado to strike the state.
- March 29, 1998: An F4 and an F3 tornado that were part of a larger outbreak tore through the towns of Comfrey and St. Peter. They killed two and caused damage in the millions of dollars in Minnesota's earliest recorded tornado outbreak.
[edit] Fall
Autumn weather in the Minnesota is largely the reverse of spring weather. The jet stream, which tends to weaken in summer, begins to re-strengthen, leading to a quicker changing of weather patterns and an increased variability of temperatures.<ref> Jet Stream. Univeristy of Illinois. Retrieved on 2006-11-23. </ref><ref> Local Climate Records. National Oceanic and Atmospheric Administration. Retrieved on 2006-11-23. </ref> Cold temperatures begin to move in with each successive storm system and rain begins to change over to snow, generally in October. The wide variance in temperatures in Minnesota is most noticeable in the fall, with summer-time heat still prevalent in the southern U.S., but cold air quickly building up in Canada. Minnesota is in a location where both air masses can affect its weather in a short period of time. As the autumn continues, storm systems become increasingly stronger. By late October and November these storm systems become strong enough to form major winter storms. Some of Minnesota's largest blizzards have come during the middle part of the fall:
- November 11, 1941: Southern and eastern Minnesota were surprised by the Armistice Day Blizzard. Temperatures in the 60's °F (16 ° C) on the morning of November 11th dropped into the single digits (−15 ° C) by the morning of November 12th, bringing it with them 27 in (68 cm) snowfall totals and 60 mph (97 km/h) winds. 154 people died in this blizzard, 49 of them in Minnesota.<ref> Armistice Day Storm. National Oceanic and Atmospheric Administration. Retrieved on 2006-11-23. </ref><ref> Tuesday, Nov. 12, 1940: Armistice Day blizzard. Minneapolis Star Tribune. Retrieved on 2006-11-23. </ref>
- October 31, 1991: Most of eastern Minnesota was rocked by the Halloween Blizzard. A band of snowfall of 24+ in (60+ cm) fell from the Twin Cities north to Duluth. It is the largest single snowfall producer in Minnesota's history.<ref> Top 5 weather events of the 20th Century. Minnesota Climatology Office. Retrieved on 2006-12-03. </ref>
[edit] Minnesota weather extremes
| Minnesota weather extremes<ref name = extremes /> | |||
|---|---|---|---|
| Event | Measurement | Date | Location |
| Temperature | |||
| Lowest Temperature | −60 °F (−51 °C) | February 2, 1996 | Tower |
| Highest Temperature | 114 °F (46 °C) | July 6, 1936 July 29, 1917 | Moorhead Beardsley |
| Precipitation | |||
| Most precip in a year | 53.52 in (135.9 cm) | 1991 | St. Francis |
| Least precip in a year | 6.37 in (16.18 cm) | 1976 | Ortonville |
| Most snowfall, 24 hours | 36 in (91.4 cm) | January 7, 1994 | Lake County |
| Most snowfall, one storm | 47 in (119.4 cm) | January 6 – 8 1994 | Lake County |
| Most snowfall, season | 170 in (431.8 cm) | 1949 – 1950 | Grand Portage State Park |
| Barometric Pressure | |||
| Highest Barometric Pressure | 31.11 in (1053.5 mb) | January 21, 1922 | Collegeville |
| Lowest Barometric Pressure | 28.43 in (962.7 mb) <ref> Storm Data and Unusual Weather Phenomena (PDF). National Oceanic and Atmospheric Administration. Retrieved on 2006-11-20. </ref> | November 10, 1998 | Albert Lea Austin |
[edit] See also
[edit] References
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