Climate of Chicago
All four seasons are distinctly represented: Winters are cold and often see snow with below 0 Celsius temperatures and windchills, while summers are warm and humid with temperatures being hotter inland, spring and fall bring bouts of both cool and warm weather and fairly sunny skies.
Annual precipitation in Chicago is moderate and relatively evenly distributed, the driest months being January[1] and February[2] and the wettest July[3] and August.
However, in late January 2019, a violent polar vortex drifted southward, enveloping the city in new record-breaking temperatures as low as −23 °F (−31 °C) on January 30, though the city just missed out on tying the all-time record low maximum temperature, recording a high of −10 °F (−23 °C) one day during the outbreak.
[30][31][32] The warming effect of Lake Michigan during the winter makes subzero temperatures somewhat less common on the lakefront than in the more inland parts of the city.
Based on 30-year averages obtained from NOAA's National Climatic Data Center for the months of December, January and February, The Weather Channel ranked Chicago the sixth-coldest major U.S. city as of 2014.
[34] Thunderstorms can occur any time of the year but are most prevalent in the springtime as the city's central location within the United States, as well as its lakeside location, makes it a center of conflicts between large volumes of warm and cold air, which can trigger a wide variety of severe weather.
[35] Twelve years later, Opening Day for the Chicago White Sox was postponed due to another 9-inch (23 cm) snowfall that had occurred on April 5.
[36] Even more extraordinary, over 18 in (46 cm) of snow fell on March 25–26, 1930, which remains one of the city's five biggest recorded snowstorms despite it occurring past the vernal equinox.
Temperatures vary tremendously in the springtime; at 100 °F (38 °C), March is the month with the greatest span between the record high and low.
Though rare, triple-digit heat has occurred in late May at Midway Airport and in outlying suburban locations.
Typically, the last freezing low of the season on average occurs on April 13 at Midway and ten days later at O'Hare.
If the winds blow from the east, or from Lake Michigan into the city, a wide discrepancy in temperatures in a matter of miles can be found, especially on particularly warm days.
On such warm nights, especially during strong heat waves, most suburban locations drop down to between 75 and 79 °F (24 and 26 °C) but quickly rebound in the early morning hours.
During such strong heat waves, the outlying suburban areas can record temperatures more than 5 °F (2.8 °C) above city and lakeshore locations.
Further west in what would today be the near and far suburbs (e.g. DuPage County and westward), temperatures reached a blistering 110 °F (43 °C) or still higher at points during this massive heat wave.
The highest temperature recorded in Chicago during the meteorological summer months of June, July, and August, which is also additionally the all-time record high in the city, is 105 °F (41 °C), set on July 24, 1934, though at Midway Airport, a future observation site, the temperature reached 109 °F (43 °C).
Summer is both the rainiest and sunniest season in Chicago;[38] only the three months of June through August experience more than 65% of possible sunshine.
The effects of the cold front did not affect many suburban areas, as temperatures reached or exceeded 100 °F (38 °C) for a fourth consecutive day throughout much of the region.
During the summer, Lake Michigan continues to have an effect on Chicago weather, but it is not as common or as strong as it is during the spring months.
On very hot days, temperatures can still be cooler along the immediate shoreline and slightly inland of the lake if winds blow from the east.
The 2012–13 autumn/winter season would fail to produce a daily maximum temperature below freezing 32 °F (0 °C) until January 1, 2013, the first such time that has happened in Chicago weather records.
The largest snowstorm before the winter solstice dropped 14.8 inches (380 mm) at Midway Airport in December 1929.
The official reading of 105 °F (41 °C) for that day was taken at the University of Chicago campus near the shoreline off Lake Michigan.
Many suburban, exurban and rural locations have all-time records that have surpassed 110 °F (43 °C), many of which were set during a heat wave in July 1936, when a massive heat wave engulfed the entire Chicago and northern Illinois region, resulting in eight consecutive days at or above 100 °F (38 °C) at Midway Airport, peaking at 107 °F (42 °C) on July 11, 1936.
It is believed to have been created by a New York newspaper writer deriding Chicagoans' bluster as they promoted their city as the site of the 1893 Columbian Exposition.
[citation needed] The lake breeze also has other effects, including dense fog spilling into the city.
Because of the closed-loop circulation pattern with a lake breeze that moves back and forth across the city, it is thought to significantly increase low-level ozone counts.
[44] Differing wind direction on either side of the thermal dividing line allows for sharp updrafts under certain conditions, favorable to thunderstorm development.
