Snow in Seattle in Dec 2026? — Above 4 inches

- [2026-10-09] El Niño impact tracker updated Oct 9 states NOAA's October outlook calls a strong-to-very-strong El Niño event likely through January–March 2027, with the Pacific Northwest leaning warm and dry as the storm track shifts toward California. The Pacific Northwest sits on the losing side of the El Niño storm-track trade... with El Niño declared in June 2026 and NOAA's odds of a strong-or-stronger event near 90%, the coming winter leans warm and dry. (https://www.elninolive.com/impacts/pacific-northwest) - [2026-09-17] NOAA CPC's Niño 3.4 index update (cited Sept 17) showed the index at +2.0°C, up from +1.8°C in August, with a rising probability of an historically unprecedented El Niño. NOAA's Climate Prediction Center confirmed September 17 that the Niño 3.4 index has risen to plus 2.0 degrees Celsius, up from plus 1.8 degrees Celsius in August. The probability of a historically unprecedented event, one that would exceed every El Niño since 1950, has climbed from 69% to 75%. (https://snowbrains.com/el-nino-2026-27-ski-forecast/) - [2026-09-20] NOAA's CPC winter outlook for Dec 2026–Feb 2027, summarized Sept 20, puts the Pacific Northwest "leaning above normal" for temperature, meaning milder air that pushes snow levels up and increases rain vs. snow in the valleys; precipitation for the PNW is forecast as "equal chances." (https://unofficialnetworks.com/noaa-winter-weather-forecast-september/) - [2026-09-17] A moderating factor was flagged this month: NOAA's forecasters noted a negative Pacific Decadal Oscillation (PDO) could dampen El Niño's typical West Coast impacts versus historical analogs, slightly easing the PNW warm/dry signal compared to August. The more significant development in September is not the raw numbers, it is the PDO caveat. NOAA's forecasters have explicitly flagged that the negative PDO may dampen El Niño's typical West Coast impacts compared to the historical analogs. That factor directly influenced the OND temperature outlook for the Pacific Northwest, where probabilities favoring above-normal warmth were moderated compared to August. (https://snowbrains.com/el-nino-2026-27-ski-forecast/) - [2026-08-20] NOAA's official long-lead seasonal outlook (issued Aug 20, 2026) for Sept-Oct-Nov 2026 showed the highest probabilities of above-normal temperatures (>50%) for the Pacific Northwest, with a slight tilt toward below-normal precipitation across northern/eastern Washington. The September-October-November (SON) 2026 Temperature Outlook favors above normal temperatures for most of Alaska as well as the western and central Contiguous United States (CONUS)... The highest probabilities (greater than 50 percent) of above normal temperatures are forecast across southeastern Alaska, the Pacific Northwest, Northern Rockies, and adjacent areas of the Northern High Plains and northwestern California. (https://www.cpc.ncep.noaa.gov/products/predictions/long_range/lead14/fxus05.html) - [2026-10-08] NOAA CPC's latest 6-10/8-14 day outlook (issued Oct 8, 2026) shows Washington leaning above-normal ("A") temperature with below-normal ("B") precipitation signals for mid-October, consistent with the broader warm/dry seasonal lean continuing into fall. (https://www.cpc.ncep.noaa.gov/products/predictions/610day/fxus06.html) - [2026-09-28] Analog comparison from the El Niño tracker: in the two strongest modern analogs (1997-98 and 2015-16), El Niño winters produced below-normal mountain snowpack in the Cascades, with 2015-16 showing that even near-normal precipitation can still yield a "snow drought" when freezing levels run high. This El Niño is expected to continue strengthening through the end of 2026, with its peak likely arriving during late fall or early winter. A stronger event increases the chances of seeing familiar El Niño patterns, but those effects are not guaranteed or perfectly proportional to the temperature of the Pacific Ocean. (https://www.elninolive.com/impacts/pacific-northwest) - [2026-09-28] Farmers' Almanac's 2026-27 winter outlook (published within last 30 days) describes a "changeable" winter for Seattle with milder, damp stretches interspersed with colder spells, and less-dependable Cascades snow than usual. The Pacific Northwest may experience a more changeable and somewhat less dependable snow season. Milder stretches mean precipitation in the valleys will often fall as rain rather than snow, and snow in the Cascades... may be less dependable than usual. Seattle and Portland should expect a changeable winter, with mild, damp stretches between colder spells. (https://www.farmersalmanac.com/extended-forecast) - [2026-09-23] Context on typical base rates: Seattle's December climatology (Sea-Tac station) shows 1.7 in total snowfall, 2 days with new snow. Most Decembers remain free of snow. Only in one out of four years does the city receive 1.1 inches (3 cm) or more of snow for the month. This underscores that even a typical (non-El Niño) December rarely exceeds 4 inches. (https://www.currentresults.com/Weather/Washington/Places/seattle-weather-in-december.php) - [2026-10-09] No specific storm system or cold-air outbreak targeting Seattle in December 2026 has yet been identified in medium-range or seasonal guidance; forecasters emphasize that freezing-level fluctuations in individual storms, not the seasonal mean, will determine any snow events. Freezing levels in the incoming storms matter more than storm counts — that is the variable the analogs punish. (https://www.elninolive.com/impacts/pacific-northwest) - [2026-10-10] As of today, December 2026 has not begun, so the resolution source (The Weather Company dashboard for the specified Seattle station) shows no snowfall data yet for the contract period; the event is unresolved and no snow has occurred or failed to occur in December 2026. BOTTOM LINE: The dominant, well-documented current signal (confirmed through early October 2026 by NOAA CPC and independent trackers) is a strong-to-historic El Niño pushing the Pacific Northwest toward a warmer, equal-to-slightly-drier December, which historically correlates with less lowland snow in Seattle and raises freezing levels — a headwind against any single December exceeding the already statistically rare >4 inch threshold, though a negative PDO and the inherent unpredictability of individual storms leave some chance of a cold snap producing a notable snow event. NOT FOUND: No day-specific December 2026 storm forecasts exist yet (outlooks only extend ~2-4 weeks from today); no official NWS Seattle winter outlook article from the last 14 days was found; could not access live current readings on the resolution source (weather.com/kalshi dashboard) since December 2026 has not occurred.

- [2026-10-08] CPC's latest ENSO Diagnostic Discussion confirms El Niño Advisory status, with "El Niño continues to strengthen, with a strong-to-very strong El Niño likely through January-March 2027 (remaining greater than an 83% chance)" — https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.shtml - [2026-10-09] A tracker site notes the October 8 CPC update raised the odds that Oct-Dec 2026 RONI reaches historic strength to "83% for October–December" , which would exceed any three-month value since 1950 — https://www.elninolive.com/el-nino-2026 - [2026-09-18] A ski-forecast analog site states "strong El Niño winters usually produce little or no snow at Sea-Tac, and the exceptions include the record 1968-69 winter and the February 2019 shutdown" , and that NOAA's Pacific Northwest outlook tilts warm but is tempered by a negative PDO — https://www.invictussnowfighters.com/winter-2026-27-outlook-pacific-northwest - [2025-05-24 approx, dated article] A Lynnwood Times report on the emergent El Niño states that in the Pacific Northwest "El Niño tends to shift the Pacific jet stream southward, steering storms away from Washington state resulting in warmer winters that are drier than average, with reduced mountain snowpack" — https://lynnwoodtimes.com/2026/05/24/el-nino/ - [2026-09-21 approx] A broader winter-outlook summary of NOAA's CPC December 2026-February 2027 forecast notes for the Pacific Northwest: "leaning above normal [temperature]. Milder air pushes snow levels up, and valley precipitation falls as rain more often than usual" , while precipitation outlook is "equal chances" — https://unofficialnetworks.com/noaa-winter-weather-forecast-september/ - [historical base rate] Climate normals (1991-2020) show Seattle's average December snowfall is only about 1.6 inches, per long-term NWS/NCEI records — https://www.extremeweatherwatch.com/cities/seattle/month-december - [2010-2023 record] Actual December snowfall totals at SeaTac over the last 14 years show only 2 of 14 years (2021: 5.8", 2022: 4.7") exceeded 4 inches, and most years saw 0-1 inch — https://www.currentresults.com/Yearly-Weather/USA/WA/Seattle/recent-12_december-seattle-temperature-precipitation.php - [general] A seasonal climatology site notes Seattle sees "no snow" in most individual winter months except rare events, and the city averages just one day a year when snow on the ground reaches 3 inches or more — https://www.currentresults.com/Weather/Washington/Places/seattle-weather-averages.php - [2024-08-27 approx, prior-year reporting] A KING5 piece on La Niña (opposite ENSO phase) found that over 25 La Niña winters since 1954, "Seattle snow totals have typically been higher than normal during La Niña winters. Normal for the season is 5 inches but the 25 La Niña winters averaged 11.5 inches per year" — this is the opposite phase from the current strong El Niño, implying the opposite (lower) tilt applies now — https://www.king5.com/article/weather/la-nina-winter-expected-western-washington/281-7810baca-d903-4514-8c7f-4d2d7d9e5a3b - [2026-04-25 approx] A regional climate blog reviewing the prior (weak La Niña) winter found that despite the typically favorable cold-season pattern, Seattle saw essentially no measurable snow: "it snowed for all of 73 minutes in Seattle over a course of two days, and never with temperatures cooler than 37 degrees. It officially counted as a 'trace' of snow" — illustrating that even favorable ENSO setups frequently fail to produce lowland snow — https://emeraldcityweather.com/seattle-warmest-la-nina-winter-on-record/ - [2026-04-25 approx] The same blog's follow-up on a potential Super El Niño observes a past comparable event as a weak test case that "failed in spectacular fashion," and notes that even historical Super El Niño years "ending up below average for snowpack, were not 'super' far below average" — https://emeraldcityweather.com/super-el-nino-seattle-pacific-northwest-impacts-2026/ BOTTOM LINE: The long-run base rate for Seattle December snowfall exceeding 4 inches is low (roughly 2 of the last 14 Decembers, ~14%, against a 1991-2020 December average of only ~1.6 inches), and the current climate driver — a historic-strength El Niño confirmed by NOAA/CPC in October 2026 — typically pushes Seattle winters warmer and drier with less lowland snow, which should skew the outside-view probability for ">4 inches" below the unconditional historical base rate, though El Niño is not a perfect predictor and occasional cold snaps/convergence-zone events can still deliver outsized single-storm totals. NOT FOUND: No direct NWS/CPC analog study quantifying exact December snowfall probabilities conditional specifically on "historic/record" El Niño strength (as opposed to generic "strong El Niño") was found; no betting-market or prediction-market historical track record specific to this Seattle snowfall contract was found.

YES means: Seattle (per the SeaTac/designated station on The Weather Company's Kalshi dashboard) records more than 4.00 inches of total snowfall for calendar December 2026, triggering the contract to resolve Yes. - [2026-09-26] A Pacific Northwest industry outlook compiling NOAA and independent climatologists notes two wildcards this year: a negative Pacific Decadal Oscillation that could blunt the warm signal on the coast, and the possibility of one or more cold-air outbreaks across the northwest corner of the continent, with the PDO "may dampen the typical impacts of a strong El Niño in certain areas." (https://www.invictussnowfighters.com/winter-2026-27-outlook-pacific-northwest) - [2026-09-26] UW atmospheric scientist Cliff Mass's August 2026 analysis, cited in the same outlook, argues the almanacs both flag late December, mid-January, and mid-February, and Cliff Mass expects near-normal mountain snowpack and above-normal moisture, which for the lowlands means the snow line is the whole story. Mass's mechanism is a deep North Pacific low driving enhanced moisture into the coast — exactly the ingredient needed if cold air intrudes simultaneously. (https://www.invictussnowfighters.com/winter-2026-27-outlook-pacific-northwest) - [2026-10-01] USDA/NIFC's October 1 monthly seasonal outlook confirms El Niño continues to rapidly strengthen, with central Tropical Pacific sea surface temperature anomalies more than 2°C above average, the threshold for a very strong El Niño, and a greater than 95% chance of a very strong El Niño continuing into the winter , while the PDO remains weakly negative and likely to remain negative through the outlook period — the negative PDO is the key mechanism forecasters say could allow cold intrusions despite the dominant El Niño warmth. (https://www.nifc.gov/nicc-files/predictive/outlooks/monthly_seasonal_outlook.pdf) - [2026-09-17] NOAA CPC's own seasonal discussion, as summarized by a ski-forecast tracker, states NOAA's forecasters have explicitly flagged that the negative PDO may dampen El Niño's typical West Coast impacts compared to the historical analogs, directly influencing the OND temperature outlook for the Pacific Northwest, where probabilities favoring above-normal warmth were moderated compared to August. (https://snowbrains.com/el-nino-2026-27-ski-forecast/) - [Historical analog, Dec 1990] Seattle's most extreme single-event precedent: a Puget Sound convergence zone combined with an arctic outbreak on Dec. 18, 1990 produced by the end of the day, Seattle was buried in 12 inches of snow — demonstrating a single convergence-zone/arctic-outflow event can blow past the 4-inch threshold in under 24 hours regardless of the seasonal mean. (https://seattleweatherblog.com/snow/the-mother-of-all-convergence-zones/) - [Historical analog, Dec 1996] The same compiled history notes Dec. 26-29 Seattle had 12-18" of snow turn to 2+ inches of rain and 50+ degrees , an event that occurred as ENSO was transitioning toward El Niño, showing a warm-mode winter does not preclude a major December snow event. (https://emeraldcityweather.com/historic-super-el-nino-scenarios-seattle-pacific-northwest-california/) - [2026-09-26] The outlook piece explicitly frames this as a plausible 2026-27 scenario, citing meteorologist Scott Sistek: "if a record El Niño sets up an anomalous ridge over Alaska that forces arctic air south, and a warm, wet El Niño-fueled storm runs into it, you get a December 1996 scenario" — described as a live scenario forecasters are watching, not a historical curiosity. (https://www.invictussnowfighters.com/winter-2026-27-outlook-pacific-northwest) - [2026-09-26] On strong-El-Niño base rates specifically, the compiled Seattle Met data shows strong El Niño winters usually produce little or no snow at Sea-Tac, and the exceptions include the record 1968-69 winter and the February 2019 shutdown — meaning when strong El Niño winters do produce snow, totals have historically been extreme (67.5" in 1968-69) rather than marginal, so any breakout event this year is more likely to clear 4 inches than land just below it. (https://www.invictussnowfighters.com/winter-2026-27-outlook-pacific-northwest) - [2026-10-01] The NIFC outlook also flags that January finally shows clearer signs of a slightly cooler, wetter pattern beginning to take shape, with storm tracks starting to shift south enough to bring more consistent moisture and improved opportunities for snowpack — implying the cooling/moistening trend could begin forming in December, ahead of January's peak, raising the odds of a late-December cold-and-wet overlap. (https://www.nifc.gov/nicc-files/predictive/outlooks/monthly_seasonal_outlook.pdf) - [2026-09-10 cited] CPC's own September ENSO-based outlook, per the outlook compilation, explicitly notes "the possibility of one or more cold air outbreaks across the northwestern quarter of the Lower 48 states," adding only that a single outbreak is unlikely to move a 90-day average — i.e., CPC itself concedes a cold-air outbreak is plausible even though it won't show up in the seasonal mean, which is precisely the mechanism needed for a >4" December event. (https://www.invictussnowfighters.com/winter-2026-27-outlook-pacific-northwest) - [2026-09-18 approx] Oregon's state climatologist, quoted in the same compilation, is "more cautious" than Mass but still "agrees an extreme El Niño can funnel the jet stream toward Oregon and Washington and that the three previous super El Niños produced above-average snowpack" even while expecting warm temperatures to push most precipitation to rain — leaving open the possibility that any cold snap intersecting that enhanced moisture produces an outsized lowland snow event. (https://www.invictussnowfighters.com/winter-2026-27-outlook-pacific-northwest) BOTTOM LINE: The strongest path to YES is not a seasonally "snowy" December but a short, sharp Fraser Valley/arctic-outflow intrusion colliding with an El Niño-charged, moisture-rich Pacific storm — a combination multiple named forecasters (Cliff Mass, Scott Sistek) and NOAA's own September-October discussions explicitly flag as a live 2026-27 wildcard via the negative PDO, and one with direct 20th/21st-century precedent (Dec 1990's 12", Dec 1996's 12-18") for blowing past 4 inches in a single multi-day event even in a warm-leaning winter. NOT FOUND: No forecaster has issued a specific December 2026 storm-timing forecast (guidance only extends ~2-4 weeks out); no quantified probability of a December convergence-zone/arctic-outflow event conditional on this year's specific El Niño/negative-PDO combination was found in any source.

YES means: Official Weather Company station data shows total Seattle (Sea-Tac) snowfall for December 2026 strictly greater than 4 inches. - [2023-11 (historical analog data)] Of the eight strong El Niño winters since 1950, Seattle was skunked in six of them, receiving zero snowfall , and the only two exceptions produced 22.9" (1965-66) and 67.5" (1968-69) for the *whole winter*, not December alone — meaning even in the rare productive El Niño winters, a >4" December specifically is not the norm pattern. - [2026-09-26] A Pacific Northwest industry outlook compiling NOAA/CPC data states plainly that El Niño winters in the lowland Northwest are usually mild and snow-light, and the exceptions are some of the worst winter events on record — i.e., outcomes are bimodal (near-zero vs. historic), with "near-zero" the heavy favorite. - [2026-09-26] The same source quotes CPC's own diagnostic language that this year's negative PDO (August value -1.11) "may dampen the typical impacts," and that the Gulf of Alaska warm pool "may allow for slightly cooler water to influence portions of the U.S. West coast," a mechanism that could occasionally support cold intrusions but does not reverse the base warm/dry tilt for December specifically. - [2026-10-06] NOAA/CPC's own October ENSO update (synthesized in the same outlook) keeps above-normal mean temperatures favored west of the Rockies, with the coastal Pacific Northwest tilted warm too, though those probabilities were "tempered a bit" because of the PDO, alongside a modest tilt toward below-normal precipitation over the interior Northwest , reinforcing the warm-air headwind against snow accumulation in the lowlands during December. - [2026-10-06] University of Washington's Climate Impacts Group newsletter confirms El Niño continued to intensify in the tropical Pacific this month, with positive SST anomalies currently breaking all-time daily records, and the 1-month October outlook showing elevated chances of warmer and drier than normal conditions across much of the state — a primary-source confirmation (not just a tracker site) that the warm/dry lean persists into the start of the contract's lead-in period. - [2026-09-26] Even local experts who dissent from the "warm and dry" consensus (Cliff Mass) argue for near-normal *mountain* snowpack and above-normal moisture overall, not increased lowland Seattle snow — the dissenting view still implies "moderate to strong El Niños are associated with less snowpack and drier conditions," with only "very strong" El Niños bringing near-normal snowpack , a mountain-elevation claim that does not translate into elevated odds for 4+ inches at the Sea-Tac/Seattle measuring station. - [2026-09 undated, Old Farmer's Almanac] Despite forecasting above-normal snowfall for the region overall, the Almanac's own 12-month outlook names late December, mid-January, and mid-February as the snowiest periods, with winter temperatures warmer than normal — splitting the "snowiest" window across three months, which dilutes the odds that December alone (vs. January or February) is the month that clears a >4" threshold. - [historical/structural] Seattle Met's tally, now a widely cited authority on this exact question, found of the eight El Niño winters since 1950 that meet the definition of "strong," Seattle was skunked in six of them, as in, the city received zero snowfall for the entire season — a 75% "zero" rate across full winters in strong-El-Niño years is a stronger headwind than the unconditional ~14% base rate (2/14 years) for December alone cited by colleagues, since this year's El Niño is being forecast as stronger than "strong" (historic/record-setting). - [2026-10-02] The most recent National Weather Service Seattle Area Forecast Discussion on file (Oct 2) describes only zonal flow aloft with a weak system, warm and dry conditions over the weekend as an upper-level ridge builds over the Pacific Northwest, and cooler and dry conditions the following week — no cold-air/snow signal is present even in the short-range guidance closest to the market's start, underscoring that no snow-producing setup has yet emerged heading into the contract period. - [resolution-technicality] The market's rules require "initial non-preliminary official values" from The Weather Company's dashboard and note that preliminary readings may change and daily reports can be missing/incomplete; any ambiguous, trace, or borderline-measured snow event close to the 4" line carries resolution risk toward No if data is reported as "trace" or incomplete under the stated correction/contingency provisions, as has occurred in past marginal Seattle snow events. BOTTOM LINE: Every independent line of evidence — strong-to-historic El Niño climatology, the current (Oct 2-8) short-range NWS and CPC guidance, and the long-run pattern that strong El Niño winters in Seattle are binary (mostly zero, rarely enormous) — points to low-probability, status-quo-favoring conditions for December 2026, with no concrete storm signal yet identified and several structural/resolution technicalities (trace readings, monthly split of "snowiest" windows across Dec/Jan/Feb) that further favor a No outcome. NOT FOUND: No day-specific or week-specific December 2026 storm/cold-outbreak forecast exists yet (guidance only extends to mid-October); no official NWS Seattle "winter outlook" article dated within the last 14 days was located; could not verify live current readings on the weather.com/kalshi resolution dashboard since December 2026 has not occurred.