Highest temperature in Seattle on May 20, 2026?
Short Answer
Both the model and the market expect the highest temperature in Seattle on May 20, 2026, to be between 66° and 67°, with no compelling evidence of mispricing.
1. Executive Verdict
- Explicit forecast for May 20, 2026, was a high temperature of 64°F.
- Major forecast services typically demonstrate high accuracy for short-term predictions.
- Local weather phenomena may cause significant localized temperature spikes.
- Broader meteorological outlook indicates no heatwave potential for mid-May.
- US-China tariff announcements are expected by May 22, 2026.
Who Wins and Why
| Outcome | Market | Model | Why |
|---|---|---|---|
| 74° or above | 1.0% | 0.5% | Forecasts for May 20, 2026, explicitly indicate temperatures in the mid-60s, making 74° or above unlikely. |
| 68° to 69° | 42.0% | 32.5% | Weather reports and forecasts indicate temperatures in the mid-60s, with general accuracy for short-term predictions. |
| 66° to 67° | 33.0% | 37.3% | The explicit forecast is 64°F, and reports suggest mid-60s, aligning with accurate short-term predictions. |
| 70° to 71° | 19.0% | 14.3% | Forecasts indicate mid-60s temperatures, suggesting 70° to 71° is less probable given short-term prediction accuracy. |
| 65° or below | 4.0% | 11.0% | The explicit forecast for May 20, 2026, is 64°F, consistent with reports of mid-60s. |
Current Context
Seattle's weather on May 20, 2026, showed a specific forecast and actual conditions. The forecast for the highest temperature in Seattle on May 20, 2026, was 64°F [^]. Weather reports for May 19-20, 2026, indicated that the city experienced mostly cloudy conditions with isolated sprinkles and temperatures ranging from the mid-60s to mid-70s [^][^]. These conditions were observed as a ridge of high pressure began to strengthen in the region [^][^].
Prediction markets in 2026 covered diverse events, sparking significant controversy. Platforms like Polymarket were utilized in 2026 to speculate on various outcomes, including Seattle's weather, the sale of sports teams such as the Seattle Seahawks, and broader geopolitical developments, for example, the Iran deal [^][^][^][^][^]. However, the application of these markets continues to be a contentious topic, with ongoing debate surrounding their classification, particularly concerning whether they constitute a form of gambling [^][^].
2. Market Behavior & Price Dynamics
Historical Price (Probability)
Outcome probability
Date
This market has traded in a narrow range between 4% and 7%, with a sideways to downward trend. The most significant price movement was a drop from an initial price of 7% down to 4% on May 19, 2026. This move appears to be a direct reaction to weather forecasts becoming available for the resolution date. The provided context indicates that forecasts called for a high of 64°F, which is below the 66°F threshold required for the market to resolve to YES. Reports of mostly cloudy conditions further dampened expectations of a warmer day, solidifying the price at the lower end of its range.
The trading volume, while modest overall at 200 contracts, shows a notable pattern. The largest single block of trading activity occurred during the price drop to 4%, suggesting that the downward move was driven by traders acting with some conviction on the emerging weather data. Since that drop, the price has stabilized at 4%, which is acting as a support level. Market sentiment, as reflected by the chart and trading action, is strongly bearish. The current 4% price indicates that traders believe there is a very low probability that the high temperature in Seattle reached 66°F on May 20, 2026, an assessment that aligns with available weather reporting.
3. Market Data
Contract Snapshot
A "Yes" resolution for the "68° to 69°" market occurs if the maximum temperature recorded in Seattle on May 20, 2026, is between 68-69°F, as per the National Weather Service's Climatological Report (Daily); otherwise, it resolves to "No." Trading closes at 11:59 PM local time on May 20, 2026, with expiration dependent on data release but no later than May 21, 2026, at 4:00 AM EDT. The NWS Climatological Report is the exclusive data source for resolution, and traders are advised to exercise caution with preliminary NWS data, with insider trading explicitly prohibited.
Available Contracts
Market options and current pricing
| Outcome bucket | Yes (price) | No (price) | Last trade probability |
|---|---|---|---|
| 68° to 69° | $0.43 | $0.58 | 42% |
| 66° to 67° | $0.33 | $0.68 | 33% |
| 70° to 71° | $0.19 | $0.82 | 19% |
| 72° to 73° | $0.04 | $0.97 | 6% |
| 65° or below | $0.05 | $0.96 | 4% |
| 74° or above | $0.01 | $1.00 | 1% |
Market Discussion
On May 20, 2026, Seattle weather was reported as mostly cloudy with isolated sprinkles, and temperatures were expected to reach the mid-60s to mid-70s Fahrenheit [^][^]. Prediction markets for Seattle's daily high temperatures typically resolve based on official data from the Seattle-Tacoma International Airport (KSEA) station, as reported by sources such as Weather Underground [^][^][^].
4. What is the historical forecast accuracy of services like AccuWeather and The Weather Channel for Seattle temperatures in late May over the past five years (2021-2025)?
| Forecast Accuracy Range (1-3 days) | 84% to 95% for one- to three-day-out forecasts (AccuWeather and The Weather Channel for Seattle) [^][^][^][^][^][^] |
|---|---|
| Definition of Accuracy | Forecasts falling within 3°F of the actual observed temperature [^][^][^] |
| Leading Provider Ranking | The Weather Channel often ranks slightly higher in recent annual metrics [^][^][^][^][^][^] |
Weather services demonstrate high temperature forecast accuracy in Seattle. AccuWeather and The Weather Channel consistently demonstrate high temperature forecast accuracy for Seattle, Washington. Their typical accuracy for one- to three-day-out forecasts ranges between 84% and 95%. Both services define forecast accuracy as the percentage of forecasts that fall within 3°F of the actual observed temperature [^][^][^][^][^][^]. These providers frequently compete for top rankings in independent assessments, with recent annual metrics often showing The Weather Channel ranking slightly higher than AccuWeather [^][^][^][^][^][^].
Proprietary models enhance accuracy, but specific historical data is limited. To enhance forecast precision, both AccuWeather and The Weather Channel leverage proprietary models and machine learning techniques [^][^][^][^][^]. However, the provided research does not include specific historical forecast accuracy for Seattle temperatures in late May, nor for the particular 2021-2025 period. The available information discusses general forecast accuracy for Seattle or refers to accuracy over different timeframes [^][^][^][^][^][^][^][^][^][^].
5. What role could local weather phenomena, like the Puget Sound Convergence Zone or Cascade downslope winds, play in causing a significant deviation from regional forecasts on May 20, 2026?
| Forecast high temperature for May 20, 2026 | 65°F (Seattle) [^] |
|---|---|
| Phenomenon causing significant localized temperature spikes | Cascade downslope winds [^][^][^][^] |
| Other local phenomenon mentioned | Puget Sound Convergence Zone [^][^][^][^] |
Local weather events can significantly alter regional forecasts. On May 20, 2026, Seattle's regional forecast anticipated cloudy conditions with possible sprinkles and an afternoon high of 65°F [^]. However, localized weather phenomena in the area possess the potential to cause significant deviations from such regional predictions.
The Puget Sound Convergence Zone is unlikely to cause temperature deviations. One local phenomenon is the Puget Sound Convergence Zone (PSCZ), a mesoscale event characterized by westerly winds splitting around the Olympic Mountains and converging over the Puget Sound [^][^][^][^]. This typically results in a narrow band of clouds and precipitation [^][^][^][^]. For May 20, 2026, the PSCZ is not identified as a factor likely to cause a significant deviation from the predicted 65°F afternoon high temperature [^].
Cascade downslope winds could cause significant temperature deviations. Conversely, Cascade downslope winds occur when strong winds flow over mountain barriers, leading to air descent and adiabatic warming on the lee side [^][^][^][^]. This process can generate significant localized temperature spikes and strong, gusty winds [^][^][^][^]. Such a phenomenon could indeed cause a significant deviation from the 65°F afternoon high temperature forecast for May 20, 2026 [^].
6. According to NOAA climate data for Sea-Tac Airport, what is the historical distribution of daily high temperatures for May 20th from 2000-2025?
| Daily High Temperature Data (May 20th, 2000-2025) | Not aggregated in a single summary table (Bound facts) [^] |
|---|---|
| Source for Historical Daily Temperature Data (Seattle) | NOAA, NCEI Past Weather Tool, and GHCN-Daily dataset [^][^] |
| Typical May Daily Highs in Seattle | 60s°F with significant inter-annual variability [^] |
A specific historical distribution for May 20th is not readily available. Precise aggregated daily high temperature data for May 20th across the 2000-2025 period is not compiled in a single summary table. Consequently, a historical distribution for that exact date range cannot be provided based on the available information [^].
NOAA maintains comprehensive historical daily temperature data for Seattle-Tacoma. While specific aggregated data for May 20th from 2000-2025 is not directly summarized, historical daily temperature records for Seattle-Tacoma International Airport (KSEA) are maintained by the National Oceanic and Atmospheric Administration (NOAA). This data can be accessed through the National Centers for Environmental Information (NCEI) Past Weather Tool and the Global Historical Climatology Network (GHCN)-Daily dataset [^][^]. General historical records for May in Seattle typically show daily high temperatures in the 60s°F, although there is considerable variability from year to year [^].
7. How do the forecast atmospheric conditions for mid-May 2026 compare to the meteorological setup that produced the record-breaking Pacific Northwest heat dome of June 2021?
| Mid-May 2026 Forecast | Cooler, wetter conditions with strong troughs of low pressure; no heatwave potential [^][^] |
|---|---|
| June 2021 Heat Dome Cause | Quasi-stationary, high-amplitude atmospheric blocking ridge (Omega block) [^][^][^][^] |
| ENSO Condition Shift | Transition from La Niña to neutral ENSO conditions [^][^] |
The forecast atmospheric conditions for mid-May 2026 in the Pacific Northwest differ significantly from the meteorological setup that produced the record-breaking heat dome of June 2021. The June 2021 event was driven by a quasi-stationary, high-amplitude atmospheric blocking ridge, specifically an Omega block [^][^][^][^]. This meteorological setup trapped a stagnant, warm column of air over the region, which suppressed convection and caused extreme surface temperatures [^][^][^][^].
Mid-May 2026 forecasts indicate cooler, wetter conditions, not a heatwave. In contrast to the 2021 event, the Pacific Northwest for mid-May 2026 is experiencing a shift toward cooler, wetter conditions [^]. This change in the upper-level pattern has occurred following the transition from La Niña to neutral ENSO conditions, with strong troughs of low pressure moving into the region [^][^]. Meteorological forecasts for this period indicate no heatwave potential, instead expecting substantial precipitation and cooler temperatures [^][^].
8. Given the projected ENSO climate pattern for Spring 2026, what do historical trends suggest for late May temperatures in the Pacific Northwest compared to long-term averages?
| ENSO Condition | ENSO-neutral (as of May 20, 2026) [^][^][^] |
|---|---|
| El Niño Transition | Rapid shift toward El Niño (expected in coming months) [^][^][^] |
| Seattle May Avg High | 66°F (1991-2020) [^][^][^] |
The Pacific Ocean recently transitioned to ENSO-neutral conditions. As of May 20, 2026, the Pacific Ocean has reached ENSO-neutral conditions. Experts predict a rapid progression toward an El Niño phase in the upcoming months, which signifies a notable shift in oceanic and atmospheric patterns [^][^][^].
Historical trends suggest variable late May conditions in the Pacific Northwest. Late May weather in the Pacific Northwest, especially during transitions from La Niña or into neutral/El Niño phases, often experiences variable conditions. This pattern can include initial warm periods followed by cooling trends as marine air, often termed June Gloom, begins to influence the region [^][^][^].
Seattle's projected late May temperature is near its historical average. For Seattle, the long-term average high temperature for May (1991-2020) is approximately 66°F, with daily highs typically increasing throughout the month [^][^][^]. The specific forecast for Seattle on May 20, 2026, projected a high temperature of around 64°F, which is close to this long-term average [^][^].
9. What Could Change the Odds
Key Catalysts
In May 2026, key prediction market catalysts include US-China tariff announcements, which have a deadline of May 22, 2026 [^] . Pred... 2026 | Polymarket">[^]. Another significant event is the release of US inflation data, scheduled for June 10, 2026 [^].
Beyond specific announcements, ongoing bets regarding Federal Reserve interest rate cuts are considered key catalysts [^] . Similarly, speculation surrounding a potential US-Iran peace deal also constitutes ongoing bets within prediction markets [^].
Key Dates & Catalysts
- Strike Date: May 21, 2026
- Expiration: May 27, 2026
- Closes: May 21, 2026
10. Decision-Flipping Events
- Trigger: In May 2026, key prediction market catalysts include US-China tariff announcements, which have a deadline of May 22, 2026 [^] .
- Trigger: Another significant event is the release of US inflation data, scheduled for June 10, 2026 [^] .
- Trigger: Beyond specific announcements, ongoing bets regarding Federal Reserve interest rate cuts are considered key catalysts [^] .
- Trigger: Similarly, speculation surrounding a potential US-Iran peace deal also constitutes ongoing bets within prediction markets [^] .
12. Historical Resolutions
Historical Resolutions: 20 markets in this series
Outcomes: 3 resolved YES, 17 resolved NO
Recent resolutions:
- KXHIGHTSEA-26MAY18-T71: NO (May 19, 2026)
- KXHIGHTSEA-26MAY18-T64: NO (May 19, 2026)
- KXHIGHTSEA-26MAY18-B70.5: NO (May 19, 2026)
- KXHIGHTSEA-26MAY18-B68.5: NO (May 19, 2026)
- KXHIGHTSEA-26MAY18-B66.5: YES (May 19, 2026)
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