Chicago May 21 High Temp: Will It Stay Below Sixty?

Chicago’s weather markets don’t get more specific than this. The question is simple: does the highest temperature recorded in Chicago on May 21 land at 59°F or below? With the resolution window closing at noon local time today, traders have pushed the probability of that outcome to 65.5%. That’s a meaningful lean, but at roughly two-thirds confidence, a full third of the market is betting the mercury climbs higher.

Here’s what the measurements are telling us. The contract’s momentum composite, combining a 3.5% one-hour gain, a 3.5% twenty-four-hour gain, and a trend score of 18.64, points to a single driver: recent forecast data suggesting a cooler-than-seasonal pattern over northern Illinois today. The market is pricing that forecast signal directly, and traders appear to be responding to the same NWS Chicago data anyone can pull up this morning.

How the Highest Temperature Contract Works

This contract resolves based on the highest recorded temperature in Chicago on May 21, 2026, with resolution at noon. The outcome labeled “59°F or below” pays out if the official daily high reaches no higher than 59°F at the reporting station. Every other outcome band, running from 60-61°F up through 78°F or higher, pays nothing on this contract.

• YES (59°F or below): Price 0.66, implied probability 65.5%
• NO (any outcome above 59°F): Price 0.35, implied probability 34.5%

Missing the 59°F ceiling requires the temperature to breach that threshold before or at noon resolution. The National Weather Service Chicago forecast zone and official ASOS station readings determine whether that happens. A single degree makes the difference here. That’s what gives this contract its sharpest edge.

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Momentum and What the Market Is Saying

The momentum composite here is straightforward. Both the one-hour and twenty-four-hour price changes sit at plus 3.5%, and the trend score of 18.64 confirms directional conviction, not noise. The most likely driver is an updated NWS Chicago morning forecast showing temperatures holding below the 60°F threshold through midday, consistent with a cooler air mass currently sitting over the region.

Total market volume stands at $5,390, with $5,240 of that trading in the last twenty-four hours. Liquidity reads at $13,845. Volume here is well below $1 million. That matters. At this depth, a single moderate-sized trade can shift the displayed probability by several percentage points. The market is pricing uncertainty, not science, and thin liquidity amplifies that dynamic significantly.

• 1h change (+3.5%): Recent forecast updates from NWS Chicago appear to be the trigger, signaling cooler morning conditions persisting through noon.
• 24h change (+3.5%): The directional move has been consistent over the past day, suggesting traders aren’t second-guessing the cool pattern signal.
• Trend score (18.64): Above neutral, confirming the YES side has absorbed selling pressure without reversing.
• Volume ($5,390 total): Thin market. Price is sensitive to individual trades and any last-minute forecast revision before noon resolution.
• Liquidity ($13,845): Order book depth is shallow relative to most climate markets. One aggressive trader could move this contract meaningfully.

Lines Analysis: NWS Chicago and the Noon Window

The data favoring the YES outcome rests on a cooler-than-normal May pattern over the Great Lakes region this week. NWS Chicago’s morning forecast, which is the primary data source traders appear to be following, has been consistent in placing Chicago’s May 21 high below the 60°F level through the early afternoon window. May averages in Chicago run in the mid-60s to low 70s, so a sub-60 day is plausible but below typical. The market is saying the current synoptic setup makes that plausible outcome likely.

What makes the NO side real is the resolution structure itself. The contract resolves at noon, not end-of-day. If temperatures are climbing through the morning and reach 60°F before the noon cutoff, every cent on the YES side loses. Chicago’s spring mornings can warm quickly when cloud cover breaks ahead of schedule. A faster-clearing sky or a shifted warm front timing would be the specific conditions that flip this contract. NWS Chicago’s hourly temperature trend for the morning of May 21 is the single most important data input right now.

• NWS Chicago hourly temperature observations through 11:59 a.m. local time are the direct resolution input. Any reading at or above 60°F ends the YES outcome.
• Cloud cover and wind direction forecasts for the morning hours determine how quickly surface temperatures respond to solar heating.
• The current La Nina-influenced late-spring pattern over the Midwest has been suppressing afternoon highs, but that signal is weakest in the morning warm-up window.
• Any forecast revision from NWS Chicago issued before noon would immediately reprice this market given thin liquidity.

The $5,390 in total volume reflects a market that is small but directionally clear. The data favors YES. The risk is concentrated in the morning warm-up rate and whether cloud cover holds long enough to keep the official high below that 59°F ceiling at resolution time.

LINES VERDICT

Cool Hold, Data Leans YES

The NWS Chicago forecast pattern and consistent momentum both point toward a sub-60 high through noon, giving the YES outcome a credible edge. The thin liquidity and tight temperature margin mean a single forecast shift could reprice the contract sharply before resolution.

What the market says: At 65.5%, traders are moderately confident Chicago stays at or below 59°F through the noon resolution window on May 21. That is a real lean, not a near-certainty, and the shallow volume means this price is sensitive to last-minute data.

Key unknown: The NWS Chicago hourly temperature observations between sunrise and 11:59 a.m. local time are the single deciding data stream. Any reading at 60°F or above before noon resolves the contract against the YES position immediately.

Scientific and Seasonal Context

Chicago’s May climatology puts the average daily high in the mid-60s, making a sub-60 outcome a below-normal but entirely plausible result. Late May cold snaps driven by upper-level troughs are not rare in the Great Lakes region. The current synoptic pattern, featuring a cooler air mass and persistent cloud cover, aligns with the kind of setup that suppresses daytime highs even as the calendar moves toward meteorological summer. The market is not pricing a freak cold event. It is pricing a modestly cool spring day in a city where those still happen regularly in May. The gap between the 65.5% probability and the climatological base rate for sub-60 days in late May is the space where trader conviction sits.

Frequently Asked Questions

• What does 65.5% probability actually mean here? It means the market collectively estimates a roughly two-in-three chance that Chicago’s official high temperature on May 21 lands at 59°F or below before the noon resolution cutoff.
• What happens to the NO side? Any of the alternative outcome bands, from 60-61°F up through 78°F or higher, represent the NO scenario. If the official temperature reaches 60°F before noon, the YES contract pays nothing.
• What single event would move this price most? An NWS Chicago forecast revision issued this morning, or the first official hourly temperature reading approaching 60°F, would immediately reprice this contract given the thin order book.
• When does this contract resolve? Resolution is set for 2026-05-21 at 12:00:00. Only temperature readings before that cutoff determine the outcome.
• Is the $5,390 volume reliable for price signals? Volume this low means individual trades carry outsized influence on displayed probability. The 65.5% price reflects real trader positions but can shift sharply on minimal new activity.

This analysis reflects market conditions as of 2026-05-21 05:16:20. Prediction market probabilities are volatile and shift as new data and regulatory decisions emerge, especially as the 2026-05-21 12:00:00 resolution date approaches. Lines.com does not accept bets or provide financial or gambling advice. All market outcomes are uncertain.