How El Nino Affects Scandinavia: Norway, Sweden and Finland Winter Anomalies

Published: July 26, 2026 · 10 min read

The NAO Teleconnection: How El Nino Reaches Scandinavia

Scandinavia sits roughly 12,000 kilometers from the tropical Pacific, where El Nino originates. The connection between these two distant regions runs through the North Atlantic Oscillation (NAO), a seesaw of atmospheric pressure between the Icelandic Low and the Azores High. The NAO is the dominant mode of winter climate variability in the North Atlantic sector, and it is sensitive to tropical Pacific sea surface temperatures.

During El Nino, enhanced convection over the central and eastern Pacific generates a train of atmospheric Rossby waves that propagate across North America and the Atlantic basin. This wave train can disrupt the pressure gradient that defines the NAO. Research by Bronnimann et al. (2007), published in Climate Dynamics, demonstrated that El Nino conditions increase the probability of a negative NAO phase by roughly 40% compared to neutral ENSO conditions.

When the NAO goes negative, the pressure difference between Iceland and the Azores weakens. The westerly winds that normally carry mild Atlantic air into Scandinavia slacken, allowing cold, dry air from Siberia and the Arctic to push westward. The result: lower temperatures, reduced precipitation in southern Scandinavia, and heavier snowfall in the northern regions where cold air meets residual Atlantic moisture.

But the relationship is statistical, not deterministic. A study in the Journal of Climate (2014) found that of 22 El Nino events between 1950 and 2010, 13 produced a negative NAO in at least one winter month — meaning roughly 40% of El Nino events did not produce the expected Scandinavian cold signal. The 2015-16 super El Nino was a prominent example: the NAO remained largely positive through the winter, and Scandinavia experienced one of its mildest winters on record.

Winter Temperature Anomalies: Two El Ninos, Two Outcomes

The 2009-10 and 2015-16 El Nino events provide a natural experiment in how the same tropical forcing can produce opposite Scandinavian outcomes. The difference lay almost entirely in the NAO response.

2009-10: The Cold Scenario. The 2009-10 El Nino was moderate in strength, peaking at an Oceanic Nino Index (ONI) of 1.6C in December 2009. That winter, the NAO plunged to its most negative value in over 40 years, with a December-February index of -1.58 (NOAA data). Across Scandinavia, the consequences were stark. Norway's national temperature anomaly for December-February was -2.3C. Sweden recorded its coldest winter in 25 years, with Stockholm's mean temperature of -4.2C running 3.1C below the 1961-1990 baseline. Finland's Lahiti region saw anomalies of -3.8C, and Helsinki recorded 82 consecutive days with snow cover, the longest stretch since 1987.

Snowfall was abundant. Oslo recorded 132 cm of cumulative snowfall that winter, against a long-term average of 88 cm. Swedish Lapland recorded snow depths exceeding 110 cm by February. The cold extended deep into spring: Stockholm's mean April 2010 temperature was 2.8C, a full 2C below normal.

2015-16: The Warm Scenario. The 2015-16 El Nino was one of the three strongest on record, peaking at ONI 2.6C. Despite the massive tropical forcing, the NAO barely budged. The December-February NAO index was +1.20, firmly in positive territory. The result was the opposite of 2009-10: Norway recorded temperature anomalies of +1.6C for winter, Sweden +2.1C, and Finland +2.4C. Stockholm recorded a December mean temperature of 3.1C, the second-warmest December since records began in 1756.

The Norwegian Meteorological Institute attributed this failure of the expected teleconnection to an unusually strong stratospheric polar vortex. The vortex remained stable and cold through the winter, preventing the downward propagation of El Nino's signal into the tropospheric NAO pattern. A 2017 paper in Nature Geoscience found that the 2015-16 polar vortex was the strongest in the ERA-Interim reanalysis record (since 1979), driven partly by a record-strong westerly phase of the Quasi-Biennial Oscillation (QBO).

Arctic Amplification and ENSO

Scandinavia's El Nino response is increasingly shaped by Arctic amplification — the phenomenon where the Arctic warms roughly 3-4 times faster than the global average. Between 1979 and 2021, the Arctic warmed at a rate of 0.73C per decade, compared to 0.19C per decade for the global mean (IPCC AR6, 2021).

The warming Arctic has been linked to a weakening of the stratospheric polar vortex and increased frequency of sudden stratospheric warming (SSW) events — the same mechanism that can determine whether El Nino's cold signal reaches Scandinavia. A 2022 study in Science found that the frequency of SSW events has roughly doubled since 1950, and that these events are increasingly likely to coincide with ENSO events due to Arctic-driven changes in planetary wave dynamics.

For Scandinavia, this means the El Nino-NAO link may be getting less predictable. If Arctic amplification increases the baseline probability of a negative NAO, El Nino's cold signal could become more frequent. But the 2015-16 case shows that individual events can still defy the statistical expectation. Researchers at the University of Bergen's Bjerknes Centre for Climate Research are actively studying this interaction; as of 2026, the scientific consensus is that the El Nino-NAO teleconnection remains robust but is increasingly modulated by Arctic-driven circulation changes.

Ski Tourism: Snow Reliability and Resort Economics

Scandinavia's ski tourism industry is a significant economic sector, and it is directly sensitive to the winter conditions that El Nino helps shape. Sweden alone has approximately 220 ski resorts, ranging from the major Alpine-style destinations in Are and Salen to small community slopes. The industry generates roughly 10-12 billion SEK (about 900 million to 1.1 billion euros) in annual revenue, according to SLAO, the Swedish ski area trade association.

During the cold 2009-10 El Nino winter, Swedish ski resorts recorded their highest visitor numbers in a decade. Are, Sweden's largest resort, reported 1.2 million skier-days for the 2009-10 season, a 15% increase over the previous season. Trysil, Norway's largest ski resort, saw a 12% visitor increase. The Norwegian ski industry reported total revenues of 7.2 billion NOK that winter, up from 6.1 billion the previous year.

The 2015-16 mild El Nino winter told the opposite story. Sweden's southern and central resorts — including Salen, Idre Fjall, and Romme Alpin — struggled with snow cover. Several resorts in Dalarna county delayed opening by 3-4 weeks. SLAO reported that artificial snow production increased by 35% compared to the previous winter, raising operational costs. Norwegian resorts fared better in the north but saw reduced visitor numbers from the key Danish and German markets, which experienced mild weather and lower skiing demand.

The economic difference between a "good" and "bad" El Nino winter for Scandinavian ski tourism is approximately 2-3 billion SEK in revenue, factoring in lift tickets, accommodation, equipment rental, and related services. For the 2026-27 season, the industry's outcome hinges on whether the NAO cooperates.

Hydropower: Reservoir Levels and Nord Pool Prices

Norway and Sweden operate the largest hydropower system in Europe. Norway generates roughly 95% of its electricity from hydropower; Sweden about 40%. Together, they account for a large share of the Nord Pool electricity market, which covers the Nordic and Baltic countries. Reservoir levels in Norwegian and Swedish mountains function as a giant battery for the region — and El Nino can either top it up or drain it.

The hydropower sensitivity to El Nino is primarily a question of precipitation distribution. When the NAO goes negative, the storm track shifts southward. Norway's western coast — where the largest reservoirs and hydropower stations are concentrated — receives above-normal rainfall as Atlantic systems are forced around the high-pressure block over the North Atlantic. But southern Norway and southern Sweden, which sit under the high-pressure ridge in a negative NAO pattern, receive below-normal precipitation.

During the 2009-10 winter, Norwegian water reservoirs in the southwestern region (NO2 price area) were at 72% capacity by March 2010, slightly above the seasonal average of 68%. But reservoirs in the southeast (NO1) were at 55%, notably below normal, due to the cold, dry conditions under the negative NAO blocking.

The 2015-16 El Nino produced the opposite pattern. Strong westerly flow under a positive NAO brought heavy precipitation to all of Norway's coast. Reservoir levels across all Norwegian price areas exceeded 80% by spring 2016, well above the 65-70% seasonal average. Swedish reservoirs in the north (SE1 and SE2) were similarly full. This abundance pushed Nord Pool spot prices down: the average system price for Q1 2016 was 19.4 EUR/MWh, compared to 27.1 EUR/MWh in Q1 2015 and 33.5 EUR/MWh in Q1 2010.

The price spread between El Nino scenarios can be substantial. A wet, mild El Nino that fills reservoirs can depress Nordic electricity prices by 15-30% relative to a normal winter. A cold, dry El Nino that increases demand for heating while reducing reservoir inflows in key areas can push prices 20-40% above normal. For energy-intensive industries in the Nordic region — aluminum smelting, data centers, and pulp and paper — these swings translate into hundreds of millions of euros in electricity cost variability.

2026-2027 Outlook

The 2026-2027 El Nino is forecast to be a very strong event, with most dynamical models projecting ONI values above 2.0C (full forecast detail). For Scandinavia, the critical unknown is the NAO response.

Current seasonal forecast models from the European Centre for Medium-Range Weather Forecasts (ECMWF) and the UK Met Office show a slight tilt toward a negative NAO for December-February 2026-27, but the signal is weak — only a 55-60% probability, according to the July 2026 ECMWF seasonal outlook. The stratospheric polar vortex is expected to be near normal in early winter, which historically reduces the chance of sudden stratospheric warming events that can drive a negative NAO.

The Norwegian Meteorological Institute's July 2026 seasonal forecast assigns a 40% probability of a colder-than-normal winter for southern Norway and Sweden, and a 35% probability for northern Scandinavia. The remaining probability is for near-normal or above-normal temperatures. On precipitation, the ECMWF forecast shows a wet signal for western Norway and a dry signal for southern Sweden and Finland — a pattern consistent with a weak negative NAO.

For the Nordic electricity market, the reservoir situation at the start of winter 2026-27 will be a key variable. As of July 2026, reservoir levels across Norway are at 68% of capacity, close to the seasonal median. If this holds through autumn, the system enters the 2026-27 winter in a neutral position — neither drought-stressed nor unusually flush.

The Nordic power system also has more interconnector capacity than during past El Nino events. The North Sea Link (1,400 MW to the UK), NordLink (1,400 MW to Germany), and new Swedish-Danish cables mean that Nordic electricity prices are more tightly coupled to continental European markets than in 2009-10 or 2015-16. This interconnector capacity reduces — but does not eliminate — the sensitivity of Nordic prices to El Nino-driven reservoir levels.