Short Answer

At least 2 inches of snow is expected in Chicago in December 2026, with the market pricing this outcome at 82.0%. This probability diverges from the model's 67.4%, even as NOAA's outlook favors below-average snowfall due to a strong El Niño.

1. Market Behavior & Drivers

The market's sharp increase in the probability of December snow in Chicago appears driven by a nuanced reading of the October 15 NOAA winter outlook. While the report's headline forecast favored above-average temperatures for the Great Lakes region, it also contained critical caveats. NOAA explicitly noted that seasonal snowfall forecasts are unreliable more than a week out and that Chicago has roughly equal chances for above- or below-normal precipitation. The contract price subsequently climbed from 60% to 82%.
This price action suggests traders focused on the report's stated uncertainty regarding snowfall rather than its temperature forecast. The initial 60% price may have reflected an underweighting of the historical probability of December snow in Chicago, possibly in anticipation of a straightforward "warm winter" report. The market's rally to 82% indicates a correction toward the high historical likelihood of at least some snow during the month, once the full, more ambiguous details of the forecast were priced in.
  • Market probability for above 2 inches of snow remains high for December 2026. Strong El Niño and NOAA outlook favor below-average snowfall and warmer temperatures.

Who Wins and Why

Outcome Market Model Why
Above 2 inches 82.0% 67.4% NOAA's winter outlook favors above-average temperatures, correlating with lower Chicago snowfall due to El Niño.
Above 6 inches 45.0% 35.8% NOAA's winter outlook favors above-average temperatures, correlating with lower Chicago snowfall due to El Niño.
Above 8 inches 23.0% 31.4% NOAA's winter outlook favors above-average temperatures, correlating with lower Chicago snowfall due to El Niño.
Above 4 inches 60.0% 41.3% NOAA's winter outlook favors above-average temperatures, correlating with lower Chicago snowfall due to El Niño.
Above 10 inches 54.0% 31.4% NOAA's winter outlook favors above-average temperatures, correlating with lower Chicago snowfall due to El Niño.

Current Context

Official forecasts favor warmer December conditions; snowfall prediction remains difficult. As of October 15, 2026, NOAA's winter outlook for December 2026–February 2027 favors above-average temperatures across the northern U.S., with the strongest odds for warmer-than-normal conditions in the Great Lakes and upper Mississippi Valley [1][2]. NOAA does not issue reliable seasonal snowfall forecasts due to unpredictability beyond approximately one week [1]. For Chicago, NOAA's seasonal precipitation outlook indicates effectively equal chances for above or below normal precipitation, while CPC guidance favors below-normal precipitation in parts of the Great Lakes; this is not a strong Chicago-specific forecast [3][2]. A strong El Niño typically shifts the storm track south and east, which may lead Chicago to experience more mixed precipitation like sleet, wet snow, or freezing rain, and any snow may melt faster [4][1][3]. The next three-month outlook update from NOAA is scheduled for November 19, 2026 [1][2]. Specific snowfall forecasts become materially more informative 7-10 days before any individual December storm [1][2].
Chicago's December snowfall normal is 7.6 inches; market signals are volatile. Chicago O'Hare's 1991–2020 December normals are a mean temperature of 30.5°F, a normal high of 36.6°F, a normal low of 24.4°F, 2.11 inches of precipitation, and 7.6 inches of snowfall [3][5][6]. The daily normal snowfall increases from about 0.2 inch early in December to about 0.3 inch late in the month [3][5][6]. This 30-year climate baseline provides the appropriate comparison for future forecasts and observed snowfall [5][6][7]. Prediction market readings are inconsistent across venues and should be considered volatile, not authoritative [8][9]. A market-data review on October 22, 2026, estimated Kalshi's Chicago December 2026 market median at 4.7 inches, suggesting traders leaned below the 7.6-inch normal [9]. This review cautioned that markets are thinly traded and the season will settle on The Weather Company data, a change from the prior season's NWS report [9]. Kalshi's displayed page showed non-monotonic probabilities (86% for >4 inches, 53% for >6 inches, and 67% for >8 inches), likely indicating thin trading, stale quotes, or display issues [8][9]. Robinhood and Coinbase also list Chicago December 2026 snowfall contracts tied to official O'Hare/CLIORD-style observations, but available search snippets did not provide dependable live probabilities to establish a cross-platform consensus [10][11].
Sources (11)
  1. 1El Nino looms large over U.S. Winter Outlook | National Oceanic and Atmospheric Administrationnoaa.gov
  2. 2Climate Prediction Center - Seasonal Outlookcpc.ncep.noaa.gov
  3. 3Latest NOAA winter weather maps: – NBC Chicagonbcchicago.com
  4. 4Chicago winter weather outlook 2026-2027: Strong El Niño favors warmer temperatures, less snow - CBS Chicagocbsnews.com
  5. 5December Normals for Temperature, Precipitation and Snowfall for Chicago, ILweather.gov
  6. 6Chicago (O'Hare) 1991-2020 Climate Normalsweather.gov
  7. 7U.S. Climate Normals | National Centers for Environmental Information (NCEI)ncei.noaa.gov
  8. 8Snow in Chicago in December? Odds & Predictions 2026kalshi.com
  9. 9Snowfall Prediction Markets vs NWS: Boston, Chicago, Denver & Morepredictionscout.com
  10. 10Snow in Chicago in Dec 2026 Climate Prediction Marketrobinhood.com
  11. 11Snow in Chicago in Dec 2026? | Prediction Marketscoinbase.com

2. Price Chart

Historical Price (Probability)

Outcome probability
Date

3. Significant Price Movements

Notable price changes detected in the chart, along with research into what caused each movement.

Outcome: Above 10 inches

📉 October 23, 2026: 19.0pp drop

Price decreased from 73.0% to 54.0%

What happened: The primary driver of the 19.0 percentage point price drop was likely the market's reaction to the National Oceanic and Atmospheric Administration's (NOAA) December 2026–February 2027 winter outlook, announced October 15, 2026 [1]. This outlook favored above-average temperatures across the Great Lakes/Midwest and indicated that strong El Niño analogs historically lead to below-average snowfall in the region [1]. Given Chicago's December normal snowfall is 7.6 inches [2], this official climate signal provided a strong fundamental reason for a drop in the probability of exceeding 10 inches, even with the price movement lagging the initial news dissemination by several days [3]. Social media activity was not identified as a factor for this movement.

Outcome: Above 12 inches

📉 October 22, 2026: 85.0pp drop

Price decreased from 86.0% to 1.0%

What happened: The primary driver of the 85.0 percentage point drop on October 22, 2026, appears to be the widespread reporting of the NOAA/NWS winter outlook, which indicated a strong El Niño favoring above-normal temperatures and likely less snow in Chicago for December 2026 [4][3][5][6]. News outlets disseminated this meteorological consensus around the time of the market movement, leading traders to significantly reduce the probability of exceeding 12 inches of snow [4][3][5][6][7]. No specific social media activity from key figures or viral narratives were identified as influencing this price movement. Therefore, social media was irrelevant in this instance.

📈 October 11, 2026: 74.0pp spike

Price increased from 12.0% to 86.0%

What happened: The provided research does not identify a clear primary driver for the 74.0 percentage point price spike on October 11, 2026, for the "Above 12 inches" outcome [8]. No specific social media activity or traditional news event could be independently tied to this movement [8]. Later seasonal outlooks (October 15-16, 2026) from NOAA and NWS Chicago actually favored above-normal temperatures and suggested below-average Midwest snowfall due to a strong El Niño, which would typically depress, not increase, such a market [3]. Therefore, based on the available information, social media activity was irrelevant to this specific price movement.

Outcome: Above 4 inches

📉 October 16, 2026: 87.0pp drop

Price decreased from 98.0% to 11.0%

What happened: The primary driver for the 87.0 percentage point drop in the "Above 4 inches" outcome was the National Oceanic and Atmospheric Administration's (NOAA) winter outlook. Released on October 15, 2026, this official announcement favored warmer-than-average conditions and, using strong El Niño analogs, suggested below-average seasonal snowfall for the Great Lakes region, including Chicago [1][6]. This significant traditional news release directly preceded the market's decline on October 16, 2026, consistent with a reduced probability of substantial snow [1]. Social media activity was not a primary driver or contributing factor, as no relevant posts or narratives were identified in the available information.
Sources (8)
  1. 1El Nino looms large over U.S. Winter Outlook | National Oceanic and Atmospheric Administrationnoaa.gov
  2. 2Chicago (O'Hare) 1991-2020 Climate Normalsweather.gov
  3. 3'Super' El Niño Winter Weather Outlook Is Here, What Does It Mean for Chicago?news.wttw.com
  4. 4Latest NOAA winter weather maps: – NBC Chicagonbcchicago.com
  5. 5Fall and winter weather predictions for Chicago 2026-2027: What El Niño could mean - CBS Chicagocbsnews.com
  6. 6Chicago winter weather outlook 2026-2027: Strong El Niño favors warmer temperatures, less snow - CBS Chicagocbsnews.com
  7. 7El Niño Could Mean A Milder Chicago Winter. But Keep Your Snow Shovel Handyblockclubchicago.org
  8. 8Snow Forecast for Chicago on Dec 20 | Prediction Market Forecastpredictmarketcap.com

4. Market Data

Contract Snapshot

This Kalshi market resolves "YES" if total snowfall in Chicago during December is above 2 inches, and "NO" if it is 2 inches or less. The market is set to pay out by January 1, 2027. A specific weather source and station are used to determine the official snowfall measurements for settlement.

Available Contracts

Market options and current pricing

Outcome bucket Yes (price) No (price) Last trade probability
Above 2 inches $0.88 $0.30 82%
Above 4 inches $0.74 $0.56 60%
Above 10 inches $0.41 $0.94 54%
Above 6 inches $0.67 $0.51 45%
Above 8 inches $0.33 $0.73 23%
Above 12 inches $0.68 $0.99 1%

Market Discussion

As of October 23, 2026, NOAA's December 2026–February 2027 outlook favors above-normal temperatures across Chicago due to a very strong El Niño, with strong El Niño analogs suggesting below-average regional snowfall [1][2][3][4]. Prediction markets as of October 22–23, 2026, appear to reflect this, pricing a median December snowfall of about 4.7 inches, which is below the 7–7.6 inch climatological normal for Chicago [5][6]. However, NOAA cautions that seasonal outlooks do not predict snowfall totals, and market analysts report thin trading that could lead to sharp price movements [1][2][7][4][5].

Sources (7)
  1. 1El Nino looms large over U.S. Winter Outlook | National Oceanic and Atmospheric Administrationnoaa.gov
  2. 2'Super' El Niño Winter Weather Outlook Is Here, What Does It Mean for Chicago?news.wttw.com
  3. 3Climate Prediction Center - Seasonal Outlookcpc.ncep.noaa.gov
  4. 4Latest NOAA winter weather maps: – NBC Chicagonbcchicago.com
  5. 5Snowfall Prediction Markets vs NWS: Boston, Chicago, Denver & Morepredictionscout.com
  6. 6Snow in Chicago in December? Odds & Predictions 2026kalshi.com
  7. 7Winter Outlook 2026-27 Version 2weather.gov

5. Trust Index

Octagon Trust Index Kalshi 65 Caution

Order book is critically thin.

Primary risk· Trade quality

How it adds up
Integrity80% of score77Good

Market integrity is low (65), but Integrity averages all three scores, so the other two pull it up. Only a critically low score would cap the total.

Trade quality20% of score15Avoid

Includes the cost to trade: a $1,000 order can't be filled here because the order book is too thin.

Trust score65Caution

Weighted blend with hard caps — a critically weak safety pillar, or a severe trading anomaly, caps the total regardless of the rest. Full methodology · About the Trust Index

Trust profile
Integrity4 screens run · 6 don't apply
Market integrity
65Caution

Outcome can be influenced

Thin-volume movesTrade signals · high confidence

“KXCHISNOWM 26DEC” made a sharp jump with almost no trading behind it.

Screened clean
Large tradesNo single trade dominates the tape. Clear
Size patternsNo distribution read Clear
2 screens not run
Outcome control · doesn't apply to this market type
Thin-leg conviction · doesn't apply to this market type
Info fairness
80Good

Structural prior — no screens apply

No suspicious activity on any screen

Screened clean
Information exposureNo concentrated group can know the outcome materially early. Clear
4 screens not run
Move vs. catalyst · doesn't apply to this market type
Longshot repricing · doesn't apply to this market type
Pre-broadcast certainty · doesn't apply to this market type
Cross-venue timing · doesn't apply to this market type
Resolution quality
92Strong

Resolution mechanism is dependable

No suspicious activity on any screen

Resolution rules read: Clear

Liquidity
12Very thin

Hard to fill near the screen price

4 contracts · worst first · 2 below the volume floor — not scored

Above 8 inches5
Very thin · low confidence

Light recent trading — size may not fill near the screen price.

Above 2 inches8
Very thin · high confidence

Typical bar range 22.2% of price over 6 traded bars

Above 6 inches11
Very thin · low confidence

Light recent trading — size may not fill near the screen price.

Above 4 inches36
Very thin · low confidence

Light recent trading — size may not fill near the screen price.

Move quality
56Mostly confirmed

Most moves carried real volume

4 contracts · worst first · 2 below the volume floor — not scored

Above 6 inches36
Mixed · medium confidence

Volume opposes the move over 24h

Above 4 inches79
Confirmed · medium confidence

Volume is light/neutral for the move over 24h

Above 2 inches81
Confirmed · medium confidence

Volume is light/neutral for the move over 22h

Above 8 inches—
No significant move (21h)

Price was stable over the last 21 hours.

Rule clarity
100Clear

Counts toward Resolution quality, not here

4 contracts · worst first · 2 below the volume floor — not scored

Above 2 inches100
Clear · high confidence

All checks pass

objective outcome · Clearofficial source · Cleartime boundary · Clear
Above 4 inches100
Clear · high confidence

All checks pass

objective outcome · Clearofficial source · Cleartime boundary · Clear
Above 6 inches100
Clear · high confidence

All checks pass

objective outcome · Clearofficial source · Cleartime boundary · Clear
Above 8 inches100
Clear · high confidence

All checks pass

objective outcome · Clearofficial source · Cleartime boundary · Clear
Trade quality
15Avoid

Order book is critically thin

Thin market — entering or exiting at fair value will be difficult.

Outcome quality 18 (notional-weighted across 4 scored legs)

$100 order: 12.1c slippage (~21% of a 58.5c contract)

$1,000 order: book too thin to fill

$10,000 order: book too thin to fill

2 below the volume floor — not scored

Above 2 inches30Market scoreLiquidity8Move quality81Rule clarity100
Why 30
Liquidity
8 · Very thin · high confidence

Typical bar range 22.2% of price over 6 traded bars

Move quality
81 · Confirmed · medium confidence

Volume is light/neutral for the move over 22h

Rule clarity
100 · Clear · high confidence

All checks pass

objective outcome · Clearofficial source · Cleartime boundary · Clear
Above 4 inches36Market scoreLiquidity36Move quality79Rule clarity100
Why 36
Liquidity
36 · Very thin · low confidence

Light recent trading — size may not fill near the screen price.

Move quality
79 · Confirmed · medium confidence

Volume is light/neutral for the move over 24h

Rule clarity
100 · Clear · high confidence

All checks pass

objective outcome · Clearofficial source · Cleartime boundary · Clear
Above 6 inchesPrimary11Market scoreLiquidity11Move quality36Rule clarity100
Why 11
Liquidity
11 · Very thin · low confidence

Light recent trading — size may not fill near the screen price.

Move quality
36 · Mixed · medium confidence

Volume opposes the move over 24h

Rule clarity
100 · Clear · high confidence

All checks pass

objective outcome · Clearofficial source · Cleartime boundary · Clear
Above 8 inches5Market scoreLiquidity5Move quality–Rule clarity100
Why 5
Liquidity
5 · Very thin · low confidence

Light recent trading — size may not fill near the screen price.

Move quality
No significant move (21h)

Price was stable over the last 21 hours.

Rule clarity
100 · Clear · high confidence

All checks pass

objective outcome · Clearofficial source · Cleartime boundary · Clear

underwriting_v1.4 · computed Oct 23, 2026

6. What climatological evidence from El Niño patterns and NOAA forecasts supports the market consensus for below-average snowfall in Chicago for December 2026?

Normal Chicago Seasonal SnowfallAbout 38 inches [1][2]
Prediction Market Implied Median December Snowfall5.875 inches [3]
NOAA Winter Outlook (Midwest)Favors above-average temperatures and drier-than-average precipitation in parts of Great Lakes [4][1][5]
NOAA outlook and strong El Niño support below-average snowfall consensus. The market consensus for below-average snowfall in Chicago for December 2026 is significantly supported by the NOAA winter outlook and the climatological mechanisms of an anticipated strong El Niño [4][1][5]. NOAA's October 15, 2026 winter outlook predicts above-average temperatures across the Midwest and Great Lakes regions, alongside elevated odds of drier-than-average precipitation in parts of the Great Lakes [4][1][5]. The expected very strong El Niño typically reduces the frequency of storm systems crossing the Great Lakes due to a southward and eastward-shifted jet stream. Additionally, warmer temperatures increase the likelihood that marginal precipitation will fall as rain rather than snow [1][6][5].
Historical El Niño analogs generally favor below-average snowfall for Chicago. Chicago's normal seasonal snowfall averages approximately 38 inches, and past strong-to-very-strong El Niño events have reportedly correlated with below-average snowfall around the city [1][2]. December marks the beginning of the reliable snow season, with the normal first date for at least 1 inch of snow occurring on December 7 [2]. However, the NWS La Crosse regional outlook indicates that strong or very strong El Niño winters have often resulted in wet conditions in the Upper Midwest, leading to mixed seasonal snowfall outcomes [5]. Nevertheless, 7 of 9 such seasonal snow totals recorded at both La Crosse and Rochester were below their 1991-2020 normals [5].
Prediction market data aligns with expectations for modest December snowfall. A recent prediction-market snapshot showed a nearly 50% probability for Chicago to receive more than 6 inches of snowfall in December, with a market-implied median of 5.875 inches [3]. This aligns with a consensus for below-normal or modest snowfall when benchmarked against Chicago's climatological December snowfall [3].
Sources (6)
  1. 1Chicago winter weather outlook 2026-2027: Strong El Niño...cbsnews.com
  2. 2Snow Climatology for the NWS Chicago County Warning...weather.gov
  3. 3Snow in Chicago in Dec 2026? — Live Odds | Frenzy Capitalfrenzycap.com
  4. 4El Nino looms large over U.S. Winter Outlooknoaa.gov
  5. 5Winter 2026-27 Outlookweather.gov
  6. 6Chicago winter 2026-2027 forecast with El Ninofacebook.com

7. How might the November 19, 2026, winter outlook update from NOAA's Climate Prediction Center (CPC) shift the probabilities for Chicago's December snowfall?

CPC Outlook Release DateNovember 19, 2026 [1][2]
Market Implied Probability (2+ inches)62% [3][2]
Market Implied Probability (6+ inches)50% [3][2]
NOAA's upcoming outlook will influence Chicago's December snowfall probabilities. The Climate Prediction Center (CPC) is scheduled to issue its Dec–Jan–Feb 2026–27 outlook on November 19, 2026 [1][2]. This official monthly 90-day outlook provides probabilities for temperature and precipitation regimes, rather than direct forecasts for specific Chicago snowfall totals [1][4]. Its release is anticipated to shift market participants' expectations about future weather patterns, consequently impacting the implied probabilities for Chicago's December snowfall [1][2].
Current forecasts imply El Niño will reduce Chicago's snowfall odds. Pre-November indicators suggest the continuation of El Niño through the winter of 2026–27, a phenomenon generally associated with milder and drier conditions across much of the northern United States, which could potentially lower Chicago's snowfall probabilities [5]. Despite this, the market for Chicago December 2026 snowfall, which is tied to official Chicago/O'Hare National Weather Service climate observations and settles on January 1, 2027, currently indicates probabilities such as 62% for snowfall exceeding 2 inches and 50% for exceeding 6 inches [3][2].
Outlook shifts will predictably alter market snowfall probabilities. A CPC outlook update indicating a colder or wetter regime for the Midwest/Great Lakes region would likely lead to an increase in market probabilities for various snowfall thresholds [6][7][8][9]. Conversely, a warmer and/or drier outlook would likely cause these probabilities to decrease, while a neutral or 'equal chances' update is expected to elicit only a modest market reaction [6][7][8][9]. It is important to recognize that the CPC outlook offers a probabilistic regime signal and does not solely determine actual snowfall, which ultimately depends on individual December storm timing, precipitation type, and specific observations at O'Hare [3][10].
Sources (10)
  1. 1Seasonal Outlook - Climate Prediction Center - NOAAcpc.ncep.noaa.gov
  2. 2Snow in Chicago in Dec 2026? — Live Odds | Frenzy Capitalfrenzycap.com
  3. 3Snow in Chicago in Dec 2026 Prediction Marketrobinhood.com
  4. 4Three-Month Outlook Maps - Climate Prediction Center - NOAAcpc.ncep.noaa.gov
  5. 5Understanding the 2026-2027 Winter Storm Season...climeradar.com
  6. 6Snow in Chicago (O'Hare) in Dec 2026?… | Frenzy Capitalfrenzycap.com
  7. 7Snow in Chicago (O'Hare) in Dec 2026?… | Frenzy Capitalfrenzycap.com
  8. 8Snow in Chicago (O'Hare) in Dec 2026?… | Frenzy Capitalfrenzycap.com
  9. 9Snow in Chicago (O'Hare) in Dec 2026?… | Frenzy Capitalfrenzycap.com
  10. 10Snow Climatology for the NWS Chicago County Warning...weather.gov

8. How does the projected strength of the 2026 El Niño compare to the strong events of 2015-16 and 1997-98 regarding their historical impact on Chicago's snowfall?

2026-27 El Niño Strength ForecastStrong-to-very strong, comparable to 1997–98 and 2015–16 events [1][2][3]
Chance of Historic El Niño (Oct-Dec 2026)83% chance of exceeding +2.5°C seasonal RONI [1][2][3]
Chicago Snowfall (1997-98 Strong El Niño)16.3 inches (December–February) [4][5][6]
The 2026-27 El Niño is projected to be exceptionally strong, placing it in a category comparable to or exceeding the intense events of 1997-98 and 2015-16 [1][2][3]. As of NOAA's October 8, 2026 outlook, this El Niño is forecast to maintain strong-to-very strong intensity through January–March 2027. The Niño-3.4 region has already reached +2.1°C, with an 83% probability of a historic event surpassing +2.5°C seasonal RONI during the October–December period [1][2][3].
Historically, strong El Niños have been associated with significantly reduced snowfall in Chicago [4][5][6]. During the crucial December–February period, Chicago recorded only 16.3 inches of snow in 1997–98 and 16.5 inches in 2015–16. These figures represent approximately half of the normal seasonal snowfall for those respective periods [4][5][6]. The winter of 1997–98, in particular, was characterized as abnormally warm with a substantially lower than average December–February snow accumulation [4][5][6].
The 2026-27 outlook favors warmer, potentially less-snowy conditions for Chicago. NOAA's projections for winter 2026–27 indicate above-normal temperatures across Chicago and the Great Lakes, while precipitation odds in the Midwest are near equal [7][8][9]. The ENSO signal strongly suggests a warm and potentially less-snowy December 2026 for Chicago, aligning with climatological expectations and the analogs of 1997–98 and 2015–16 [1][10][7][8][9]. However, local reports emphasize that while a strong El Niño generally favors below-average snowfall in Chicago, it does not rule out the occurrence of major snowstorms, and seasonal outlooks do not provide exact snowfall predictions [7][8][9].
Sources (10)
  1. 1Climate Prediction Center: ENSO Diagnostic Discussioncpc.ncep.noaa.gov
  2. 2Official NOAA CPC ENSO Strength Probabilitiescpc.ncep.noaa.gov
  3. 3ENSO: Recent Evolution, Current Status and Predictionscpc.ncep.noaa.gov
  4. 4El Nino Primerweather.gov
  5. 5El Niño will impact Chicago's winter, but how will it affect...nbcchicago.com
  6. 6Chicago, IL Seasonal Snowfall Totals from 1884 to present!weather.gov
  7. 7El Nino looms large over U.S. Winter Outlooknoaa.gov
  8. 8El Niño impacts latest winter weather outlooks for Chicago...nbcchicago.com
  9. 9Chicago winter weather outlook 2026-2027: Strong El Niño...cbsnews.com
  10. 10How does El Niño influence winter precipitation over... - Climateclimate.gov

9. What are the key differences in snowfall measurement methodologies between The Weather Company and the National Weather Service (NWS) at Chicago O'Hare that could affect market settlement?

Official Settlement SourceNational Weather Service (NWS) Daily Climate Report [1]
Snowfall Observation MethodManual observation by FAA-contracted observers using a stick on a cleared snow board [2]
Market Data RequirementNWS official daily climate-report snowfall entries for December [3]
Market settlement for snowfall at Chicago O'Hare relies on official NWS data. The "Snow in Chicago in Dec 2026?" market will settle based on the National Weather Service (NWS) Daily Climate Report, specifically for the Chicago O'Hare station CLIORD [1]. Official NWS snowfall observations at Chicago O’Hare are conducted manually by FAA-contracted observers. These measurements involve using a stick on a cleared snow board every six hours and promptly after snowfall ceases, reporting new accumulation for that period rather than snow depth [2]. The NWS acknowledges that factors such as wind, drifting, melting, and compaction can influence these measurements, describing them as an inexact estimate, especially when temperatures are near freezing or during windy conditions [2][3].
The Weather Company's snowfall data is not considered equivalent for market settlement. It is critical for market settlement to use the official daily climate-report snowfall entries for December, rather than any unofficial storm-total reconstructions [3][1]. The Weather Company's displays are not considered settlement-equivalent, as their products may present station-level or modeled/processed weather data, and there is no established universal snowfall algorithm for O’Hare that aligns with NWS methodology [4][1]. Therefore, traders should not assume that a displayed total from The Weather Company is interchangeable with the official NWS values [4][1]. Settlement complexities can arise from distinguishing between trace and measurable snow, report revisions, rounding practices, and the timing of the final Daily Climate Report, underscoring the necessity of relying exclusively on the latest official NWS report version [1][5][6].
Sources (6)
  1. 1Snow in Chicago in Dec 2026 Prediction Marketrobinhood.com
  2. 2Weather Observations and NWS Climate Products FAQweather.gov
  3. 32011 Blizzard Storm Total Snowfall Adjusted & In-Depth...weather.gov
  4. 4Weather Prediction Markets: Trade Temp, Rain & Hurricanesbonus.com
  5. 5Snow in Chicago in March 2026? Odds & Predictionskalshi.com
  6. 6Lowest temperature in Chicago today? Odds & Predictions 2026kalshi.com

10. Beyond El Niño, what specific atmospheric patterns, like a negative North Atlantic Oscillation (NAO) or a displaced polar vortex, could lead to an above-average snowfall total in December 2026?

El Niño ForecastContinuing through winter 2026–27, favoring above-normal temperatures and below-normal precipitation in parts of the Great Lakes [1][2][3]
Upside Snow ScenarioNegative North Atlantic Oscillation (NAO) or a displaced polar vortex could lead to above-average snowfall in Chicago [1][4]
Optimal Chicago Snow ConditionsCanadian or Arctic air intrusion into the Great Lakes followed by a storm track or upper-level trough crossing the Midwest, with sufficiently cold boundary-layer temperatures and moisture [5]
A strong El Niño poses challenges for above-average December 2026 snowfall. As of October 23, 2026, a very strong El Niño is predicted to persist through winter 2026–27, favoring above-normal temperatures and below-normal precipitation in parts of the Great Lakes [1][2][3]. This establishes a hostile background state for above-average December snow. However, specific atmospheric patterns, such as a negative North Atlantic Oscillation (NAO) or a displaced polar vortex, present an important upside scenario that could lead to above-average snowfall in Chicago [1][4].
Specific atmospheric patterns facilitate significant regional snowfall events. A negative NAO phase benefits Chicago snowfall by creating blocking and high pressure near Greenland, which subsequently slows or displaces the Atlantic jet stream and supports downstream troughing and cold air over the eastern United States and Great Lakes [4]. While a strong El Niño typically favors a stronger, more stable stratospheric polar vortex, a weakened, displaced, or split stratospheric polar vortex can increase the likelihood of downstream negative Arctic Oscillation (AO) circulation, impacting surface weather [1][6][7]. Other patterns that could enhance December 2026 snow include a negative Eastern Pacific Oscillation (EPO) or an Alaskan ridge, potentially reinforced by a favorable Madden–Julian Oscillation (MJO) phase [4].
The optimal cold setup involves a multi-faceted atmospheric reversal. For Chicago, the most effective snow-producing cold setup would involve a Canadian or Arctic air intrusion into the Great Lakes, followed by a storm track or upper-level trough crossing the Midwest, combined with sufficiently cold boundary-layer temperatures and moisture [5]. The clearest path to above-average Chicago snowfall involves a temporary regime reversal, characterized by a negative AO/NAO, ideally reinforced by negative EPO/Alaskan blocking or a weakened/displaced polar vortex, in conjunction with repeated moist Midwest cyclones or a favorable Great Lakes storm track [1][2][3].
Sources (7)
  1. 1Climate Prediction Center - Seasonal Outlookcpc.ncep.noaa.gov
  2. 2'Super' El Niño Winter Weather Outlook Is Here, What Does It...news.wttw.com
  3. 3Chicago winter weather outlook 2026-2027: Strong El Niño...cbsnews.com
  4. 4Winter 2025-26 Outlookweather.gov
  5. 5The Role of a Tropopause Polar Vortex in the... - AMS Journalsjournals.ametsoc.org
  6. 6Forecast-based attribution of the role of stratospheric...egusphere.copernicus.org
  7. 7Diverse Surface Signatures of Stratospheric Polar Vortex...researchgate.net

11. What Could Change the Odds

Key Catalysts

NOAA forecasts favor above-normal temperatures in Chicago for December 2026 due to a very strong El Niño event [1][2][3]. This condition historically correlates with below-average snowfall for the region [1][2][3].
Prediction markets currently anticipate lower-than-normal snowfall for December 2026, showing a median expectation of approximately 4.7 inches [4][5]. This figure is notably below the 1991-2020 climatological normal for December snowfall in Chicago, which ranges from 7.6 to 8.5 inches [6][7][8].
NOAA updates its seasonal outlooks monthly, with the next release scheduled for November 19, 2026 [1][9]. However, seasonal outlooks do not project specific daily snowfall totals, which are generally not predictable beyond one week [1][9].

Key Dates & Catalysts

  • Expiration: January 07, 2027
  • Closes: January 01, 2027
Sources (9)
  1. 1El Nino looms large over U.S. Winter Outlook | National Oceanic and Atmospheric Administrationnoaa.gov
  2. 2'Super' El Niño Winter Weather Outlook Is Here, What Does It Mean for Chicago?news.wttw.com
  3. 3Chicago winter weather outlook 2026-2027: Strong El Niño favors warmer temperatures, less snow - CBS Chicagocbsnews.com
  4. 4Snowfall Prediction Markets vs NWS: Boston, Chicago, Denver & Morepredictionscout.com
  5. 5Snow & Rain Prediction Markets | Kalshikalshi.com
  6. 6Chicago (O'Hare) 1991-2020 Climate Normalsweather.gov
  7. 7December Normals for Temperature, Precipitation and Snowfall for Chicago, ILweather.gov
  8. 8Chicago O’Hare International Airport Climate Normals – Illinois State Climatologiststateclimatologist.isws.illinois.edu
  9. 9Climate Prediction Center - Seasonal Outlookcpc.ncep.noaa.gov