Seattle May 18 High Temp: Will It Hit 58°F?

The market has spoken, and it spoke loudly. Traders on this Seattle temperature contract have priced the 58°F-or-higher outcome at 99.8% probability, leaving essentially nothing on the table for any cooler scenario. With resolution set for May 18, 2026 at noon, this contract has one more day to run. The science and the forecast agree with the traders.

Here’s what the measurements are telling us: Seattle’s May climate pattern, combined with the current synoptic setup over the Pacific Northwest, makes a high at or above 58°F on May 18 almost certain. Late-spring temperatures in Seattle routinely reach the mid-to-upper 60s. A high of 58°F clears a bar that the city exceeds on the majority of mid-May days under normal conditions.

How the Seattle May 18 Temperature Contract Works

This market resolves YES if Seattle’s official highest temperature on May 18, 2026 reaches 58°F or above. The contract resolves NO if the day’s peak falls into any lower bracket: 56-57°F, 54-55°F, 52-53°F, 50-51°F, 48-49°F, 46-47°F, 44-45°F, 42-43°F, 40-41°F, or 39°F and below. Resolution is based on the official temperature record for that date.

• 58°F or higher (YES): 1.00 price, 99.8% implied probability.
• 56-57°F: priced near zero.
• All other brackets (39°F or below through 54-55°F): priced at effectively zero.

Missing the YES outcome requires Seattle’s high temperature on May 18 to stay below 58°F. That means a sharp cold-air intrusion, a prolonged marine layer, or significant storm system pushing through the region before noon local time. The National Weather Service would need to record a peak reading under 58°F at Sea-Tac Airport, the standard measurement station for Seattle official records. May 18 lows near 58°F are vanishingly rare in Seattle’s climate history.

Sponsored Partner

Momentum and Market Signals Pointing One Direction

The 1-hour and 24-hour price changes both read N/A, which makes sense for a contract this deep in YES territory. The trend score of 56.15 reflects steady, settled conviction rather than active repositioning. No new weather data has broken the market out of its current stance. The signal here is absence of movement, which for a 99.8% contract means everything is tracking as expected.

Total volume sits at $13,044, with $2,514 changing hands in the last 24 hours. Liquidity shows $128,094 in the order book. Volume below $1 million means this market can reprice sharply if a dramatic forecast change lands before noon on May 18. That said, at 99.8%, there is almost no room left to move upward, and the weather data would need a dramatic reversal to push price downward.

• Trader sentiment sits at 99.8% YES and 0.2% NO. The directional lean is as one-sided as prediction markets get.
• The trend score of 56.15 connects to a stable short-range forecast, not a data release or policy event.
• Total volume of $13,044 is thin. A single large trade on either side would visibly move the order book depth.
• The 24-hour price shows no movement, consistent with a market waiting for the clock to expire rather than new information.
• Open interest reads $0, indicating no unresolved positions generating additional pressure on price.

Lines Analysis: The Seattle Temperature Picture

Seattle’s climatological average high for May 18 sits comfortably above 60°F based on historical normals from NOAA’s long-period averages for Sea-Tac Airport. The 58°F threshold in this contract sits below the seasonal average, not above it. That positioning is the foundation of the 99.8% price. The market is not predicting an unusually warm day. The market is predicting a normal mid-May day in Seattle.

The scenario that breaks this contract is a strong onshore flow bringing cold marine air deep into the Puget Sound basin before Seattle’s temperature can peak. A surface trough dropping south from British Columbia, combined with persistent low clouds, can cap Seattle temperatures in the mid-to-upper 50s. That outcome is possible in May. It is not likely. Current short-range models as of May 17, 2026 do not show that setup for the 18th.

• NOAA’s short-range ensemble forecast for Sea-Tac Airport is the primary data source to watch before noon on May 18.
• Any National Weather Service advisory for a significant marine push or cold frontal passage arriving before noon would reprice this contract immediately.
• The University of Washington’s atmospheric sciences department runs high-resolution regional models for the Pacific Northwest. Their output through May 18 is consistent with an unremarkable spring day.
• Satellite imagery showing a deep marine layer moving inland before the morning hours on May 18 would be the clearest warning signal for the NO outcome.
• Any official temperature observation from Sea-Tac showing a stalled maximum in the 56-57°F range before noon would warrant reassessment.

The $13,044 total volume reflects a market that settled its opinion early and has not faced a meaningful challenge. The data favors YES, and the forecast as of May 17 supports that read. The market is pricing settled short-range meteorology, not uncertainty.

LINES VERDICT

Seattle Clears Fifty-Eight

Seattle’s mid-May climatology puts the 58°F threshold well within the normal daily range. The current forecast gives no credible signal for the kind of marine intrusion needed to suppress the high below that number.

What the market says: A 99.8% probability means the market treats this outcome as resolved. With the resolution clock expiring at noon on May 18, there is almost no room left for price to move higher, and only a dramatic forecast reversal would move it lower.

Key unknown: A rapid-onset marine layer or cold frontal passage arriving in the Puget Sound basin before the Sea-Tac temperature peaks on the morning of May 18 is the single event that could reprice this contract before resolution.

Scientific Context: Seattle’s May Temperature Climatology

NOAA’s 30-year climate normals for Seattle-Tacoma Airport place the average high temperature for mid-May between 62°F and 64°F. The 58°F threshold in this contract sits roughly 4 to 6 degrees below the seasonal average. For context, Seattle records a daily high at or above 58°F on the vast majority of days between late April and early October. The climate record does not show a Seattle May 18 high below 58°F as a frequent outcome. Marine intrusions can suppress temperatures, but sustained suppression below that level on a mid-May day requires a persistent cold pattern that current models do not show. The gap between the 58°F threshold and the seasonal average is the structural reason this market sits at 99.8%.

Frequently Asked Questions

• What does 99.8% probability mean here? It means traders have placed roughly $128,094 in liquidity behind the outcome that Seattle’s official high on May 18 reaches at least 58°F. A 0.2% residual reflects irreducible uncertainty, not a credible competing scenario.
• What does the NO outcome pay? Any bracket below 58°F, from 56-57°F down to 39°F or below, qualifies as a NO resolution. All those brackets currently trade near zero, reflecting near-zero market probability.
• What data release or event could move this price before resolution? A National Weather Service short-range forecast update showing a marine layer or cold frontal passage reaching Sea-Tac before noon on May 18 would be the primary catalyst for any price shift.
• When does this contract resolve? Resolution is set for May 18, 2026 at 12:00 PM. The official Sea-Tac Airport high temperature recorded up to that time determines the outcome.
• Is the volume reliable for reading this market? Total volume of $13,044 is thin. Liquidity of $128,094 supports stable pricing now, but low trading volume means any single large order can move the price sharply before resolution.

This analysis reflects market conditions as of 2026-05-17 09:19:07. Prediction market probabilities are volatile and shift as new data and regulatory decisions emerge, especially as the 2026-05-18 12:00:00 resolution date approaches. Lines.com does not accept bets or provide financial or gambling advice. All market outcomes are uncertain.