Chicago Midway (KMDW) Temperature Market Guide

The KMDW Automated Surface Observing System (ASOS) is located at Chicago Midway International Airport, a major commercial airport established in 1927. The station sits at an elevation of 620 feet above sea level on a flat plain approximately 40 feet above the level of Lake Michigan.

Importantly for traders, Midway is situated about 8 miles southwest of downtown Chicago and is further inland from Lake Michigan compared to the lakefront. This positioning means Midway often records warmer summer temperatures - typically 2-5°F higher than O'Hare International Airport - due to intensified urban heat island effects from surrounding asphalt, concrete, and dense urban development.

Chicago experiences a humid continental climate (Koppen classification: Dfa) characterized by four distinct seasons with significant temperature variability. Annual temperature swings often exceed 54°F between winter lows and summer highs, creating diverse trading opportunities throughout the year.

Key Climate Factors:

Lake Michigan Influence: The lake's massive thermal mass moderates temperatures, causing cooler summers and warmer winters near the shoreline. However, Midway's inland position (about 8 miles from the lake) means it experiences less direct lake moderation than lakefront stations. During summer, when winds blow from the east, temperatures along the lakeshore can be 10°F or more cooler than at Midway.

Urban Heat Island Effect: Chicago's urban core averages about 2°F warmer than surrounding rural areas, with Midway often experiencing temperatures 3-5°F higher than suburban locations due to heat absorption from pavement and buildings.

Lake Breeze Dynamics: During warm season days, a lake breeze frequently develops as cooler air over Lake Michigan flows inland to replace rising warm air over land. The strength and inland penetration of this breeze significantly impacts daily high temperatures.

Winter (December - February):
Average highs range from the upper 20s to mid-30s°F. Arctic air masses from Canada can send temperatures plummeting, while lake-effect snow events occur when cold air passes over the relatively warm lake. Midway's inland position typically means less lake-effect snow than lakefront areas, but temperature variations can be significant during cold air outbreaks.

Spring (March - May):
Highly variable temperatures as warm and cold air masses battle. Lake Michigan remains cold through spring, so easterly winds can suppress temperatures significantly. Forecasting is challenging during this transitional period, creating opportunities for informed traders.

Summer (June - August):
Average highs in the low-to-mid 80s°F, with occasional heat waves pushing temperatures above 90°F. The urban heat island effect is most pronounced during summer. Thunderstorm activity peaks in July and August, occasionally bringing rapid temperature changes. Heat waves are most intense when south or southwest airflow prevents lake breeze development.

Fall (September - November):
Gradually cooling temperatures with relatively stable weather patterns. Lake Michigan acts as a heat reservoir, keeping lakefront areas slightly warmer at night.

Watch the Wind Direction: Wind direction is perhaps the single most important factor for Chicago temperature forecasts in summer. South or southwest winds allow temperatures to climb unimpeded, while east or northeast winds bring cooler lake air inland. A forecasted wind shift mid-day can significantly impact whether temperature thresholds are reached.

Morning Lake Temperature Differential: Monitor the temperature difference between Midway and lakefront stations. Large differentials early in the day suggest strong lake breeze potential that could cap afternoon highs.

Urban Heat Island Timing: Midway's urban surroundings mean it often reaches daily highs slightly later than rural stations and maintains heat longer into the evening.

Model Performance: The HRRR model generally performs well for Chicago due to relatively flat terrain, but can struggle with lake breeze timing. The NAM often handles synoptic patterns well but may miss mesoscale lake effects.

Chicago temperature markets on Kalshi and ForecastEx resolve based on the official high temperature reported in the National Weather Service Climatological Report (CLI) for station KMDW.

Resolution Source: NWS CLI issued by the Chicago Weather Forecast Office (LOT)

Reporting Period: 12:00 AM to 11:59 PM Central Standard Time (CST). Note that during Daylight Saving Time, clocks show 1:00 AM to 12:59 AM CDT, but the official 24-hour climate day still aligns with standard time.

CLI Timing: The final CLI for the previous day is typically issued in the morning hours following the observation period.

Lake Breeze Uncertainty: Predicting the exact timing, strength, and inland penetration of lake breezes remains one of the most difficult aspects of Chicago forecasting. Models often struggle to accurately capture these mesoscale effects.

Convective Initiation: During summer, isolated thunderstorms can develop rapidly and dramatically cool temperatures. The timing and coverage of afternoon convection adds uncertainty to high temperature forecasts.

Cold Air Outbreak Timing: In winter, the exact timing of cold frontal passages determines whether cold arctic air arrives before or after the daily high is recorded.

Cloud Cover Variability: Lake Michigan can enhance cloud development, and cloud cover timing significantly impacts daily maximum temperatures.

Record High: 105°F recorded on July 24, 1934.

Record Low: -27°F recorded in January 1985.

100°F+ Days: Temperatures reaching 100°F at Midway occur infrequently - averaging less than 1 day per year based on recent decades.

Seasonal Records: Late-season warmth is possible - temperatures have reached 90°F+ as late as early October (94°F on October 6, 1963).