Highest temperature in Chicago on Sep 12, 2026?

📊 Market Summary

🌦️ Highest temperature in Chicago on Sep 12, 2026?

6 options total

🎯 Best Trade

• Action: 86° to 87° — YES @ 63%

• Confidence: 🔴 LOW · Uncertainty: MEDIUM

• Why:

• GFS is the warmest model at 87.1°F, still below this band, so 88-89°F requires an overshoot beyond every raw model output.
• The NWS point forecast of 86°F and The Weather Company's sub-84°F read both sit below this band, leaving no official support for 88°F+.
• September 2026 opened with record heat (avg 85.4°F first four days), which keeps the warm tail alive but not enough to justify a premium over the 16% price.

📈 Where the Market Stands

Verdicts compare my own read against the market price — 🟢 UNDERPRICED (market has it too low) · 🔴 OVERPRICED (market has it too high). The analysis below is the why.

🔬 9-Pillar Analysis (Meteorological Method)

🌡️ 1. Forecast Consensus

My Vegas Line reads the 86-87°F band as the clear favorite at 63%, and the NWS point forecast for the settling station (Chicago Midway, KMDW) is 86°F — the market's favorite sits exactly on the official forecast number.

📊 2. Ensemble Spread

Raw multi-model spread for Sep 12 is only 2.4°F (GFS 87.1, ECMWF 85.6, ICON 84.7), which is tight relative to the 2°F band width, so the market's concentration in one band is defensible rather than overconfident.

⏳ 3. Forecast Skill Decay

This is a same-day/next-day horizon with the station already at 73.4°F by mid-morning, so forecast skill is at its seasonal peak — no skill-decay discount applies here.

📈 4. Historical Base Rate

Climatological base rate for Chicago around Sep 12 centers on highs in the upper 70s to low 80s, but September 2026 opened with the hottest first four days on record (avg 85.4°F), so the warm tail is genuinely elevated this year.

🔀 5. Model Divergence

The outlier model is ICON at 84.7°F — if ICON is right, the 84-85°F band (16%) wins and the 86-87°F favorite dies; GFS at 87.1°F is the opposite tail that would push toward 88-89°F.

📍 6. Micro-Climate Bias

KMDW is an urban, inland station with a documented heat-island bias versus O'Hare, and the NWS point forecast of 86°F is issued specifically for this station, so the micro-climate supports the warm side rather than breaking it.

🌀 7. Storm Track

Not a tropical or severe-weather contract — no storm track applies; the only relevant synoptic feature is a warm air mass with southerly/southwesterly flow and mostly sunny skies, which is stable.

💰 8. Market Pricing

MEDIUM - the market is liquid for a weather contract ($11k volume) and the favorite sits on the official NWS number, but the 84-85°F and 88-89°F bands are both live given the 2.4°F model spread, so the tails are not dead.

⚡ 9. Contrarian Check

The main contrarian risk is that the market has crowded 63% into a single 2°F band when the model spread (2.4°F) is wider than the band itself — a one-degree miss to 85°F or 88°F collapses the favorite, and the 84-85°F band at 16% is the most likely beneficiary.

⚠️ Disclaimer: AI can make mistakes. This is not financial advice, and not a meteorological forecast — verify against NWS/NOAA and current model output before placing any trades.