User:WxGopher/ClimateSandbox

The Climate of Minnesota is typical of a continental climate with cold winters and hot summers. It is rightfully thought of as being a very cold state, but in reality the cold is just one of many types of weather that Minnesota endures. Its unique location in the Upper Midwest allows it to experience some of the widest variety of weather in the nation. Minnesota experiences everything from rain to snow, tornadoes to blizzards, droughts to floods, and temperature extremes ranging from −60 °F (−51 °C) to 114 °F (45.5 °C) as span of 174 °F (96 °C).

Each of the four seasons has its own distinct characteristics, but there enough variables that keep any season from being constant. Winter is generally cold and snowy but can see thaws and rain. Summers are generally warm and humid, but do see frequent Canadian cool fronts in which the air dries out and cools off. Fall and spring are the transition months where wild swings in the weather can be expected, and where parts of summer and/or winter can make appearances.

General climatology

Minnesota experiences temperature extremes characteristic of its continental climate, with cold winters and mild to hot summers in the south and frigid winters and generally cool summers in the north.  Each season has distinctive upper air patterns which bring different weather conditions with them.  

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. The 174 degree (96 °C) variation between Minnesota's highest and lowest temperate is the 11^th largest variation of any U.S. State, and 3^rd largest of any non-mountainous state (behind North Dakota and South Dakota).

Because Minnesota is so far from a major source of moisture, it is one of the drier states in the U.S. Average precipitation across the state ranges from around 35 in (89 cm) in the southeast to just 20 in (51 cm) in the northwest. Snow is the main form of precipitation from November through March, while rain is the most common the rest of the year. 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.

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 that region a taste of a maritime climate.

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.

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. 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. 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.

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 usually do not bring significant amounts of snow, unless they dip far enough south to tap into Gulf of Mexico moisture.

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.

Alberta Clippers

Alberta Clippers are usually the storms responsible for ushering arctic air into Minnesota. 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 not located near 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 Gulf of Mexico moisture can work its way north. 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.

Panhandle Hooks

In terms of their characteristics, panhandle hooks are nearly the opposite of Albert 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. 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 center if there is enough cold air available. A wintery mix of precipitation or rain will then often occur to the south of it. 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.

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 move in 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. 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.

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. 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.

Wind

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. 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).

Floods

Like a lot of states, Minnesota is prone to flooding in its major rivers. Minnesota has been rocked by major flooding in 2001, 1997, 1993 1969 and 1965. Unlike the other four, the 1993 flooding was mainly due to heavy late-spring and summer rains. The 1965 Mississippi flood was the worst flood in Minnesota history on that river, while the flooding in 1997 was the worst in history on the Red River in the northwestern part of the state. Heavy winter and spring snowfall, cold winter temperatures and heavy spring rains are common causes of river flooding in Minnesota.

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. 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.

Temperatures

Summer temperatures in Minnesota average in the mid 80's (30 °C) in the south to the upper 70's (25 °C) in the north. Because summer time air masses are not as volatile as in the winter, 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. Northern Minnesota is considerably cooler and less humid than southern Minnesota is during the summer months.

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.

Precipitation

The summer months of June, July and August account for around half of the annual precipitation total across the state of Minnesota. 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. 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). 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. 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.

Droughts

Like other agricultral states droughts are an annual summer concern in Minnesota, especially for farmers. The growing season in Minnesota varies from 90 days per year in the Iron Range to 160 days in southeast Minnesota. The growing season is when Minnesota averages its highest percentage of annual precipitation, so a lack of rainfall during this time period can be devastating to crops. The last major drought in Minnesota was in 1988. The period of April - July of that year was the 2^nd driest in the previous 100 years, 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. Other memorable drought years were 1976 and the Dust Bowl years of the 1930's.

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 or 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, and on average has an F5 tornado once every 25 years. Some of the memorable Minnesota tornadoes and outbreaks are:

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. Storm systems associated with the Pacific Ocean again become more common, with each successive storm system bringing colder temperatures until the 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 fall goes on, 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: