How Will El Niño Affect Manitoba’s Winter?

How Will El Niño Affect Manitoba’s Winter?

How Will El Niño Affect Manitoba’s Winter?

By Scott Kehler, M.Sc. President and Chief Scientist at Weatherlogics Inc.

El Niño is this fall’s weather buzz word. But what on Earth is El Niño and why do we care? In short, El Niño refers to unusually warm waters in the central Pacific Ocean. Because the Pacific is a massive body of water, covering about one third of the Earth’s surface, it plays a big role in controlling global weather patterns. The impacts of El Niño are often felt right here in Manitoba, especially during the winter. For more information on how these conditions initially develop in the ocean, see this article.

El Niño is part of a series of oceanic patterns called ENSO, or El Niño-Southern Oscillation. The Climate Prediction Center in the United States tracks ENSO, the state of the central Pacific Ocean as it varies from warm to cold. During the cold phase, the opposite of El Niño, the conditions are referred to as La Niña. Since 1950, the Climate Prediction Center has identified 20 La Niña events and 23 El Niño events. However, there are also periods in between La Niña or El Niño where ocean temperatures are “normal.” These in-between periods are referred to as neutral conditions.

In Manitoba, our weather is affected the most by ENSO (El Niño or La Niña) during the winter. On average, El Niño tends to bring warmer and drier winters, while La Niña tends to bring colder and snowier winters. But it’s not always that simple.

There have been warm La Niña winters and cold El Niño winters, so the winter forecast cannot be based on these events alone. One important factor in gauging the possible impact of El Niño or La Niña is its strength. The warmer the central Pacific Ocean, the “stronger” the El Niño event. This year’s El Niño currently has ocean temperatures that are more than 1.5˚C warmer than normal. Such warm temperatures cause the El Niño to be categorized as “strong”, which makes its impact on Manitoba weather a bit more certain. Historically, strong El Niño events are almost always associated with warm winters in Manitoba. The correlation isn’t 100 per cent, but it is among the strongest predictors of our winter weather. Snow is less correlated than temperature, but a strong El Niño increases the chance of a dry winter.

While winter is important to help the land rest, summer weather is more important for determining the success of a growing season. The correlation between El Niño and summer weather in Manitoba is not as strong as its correlation with winter weather. The impact on temperatures is neutral, neither favouring warmer or colder conditions on average. However, El Niño is often associated with stormier summers, bringing more chances for rain and severe weather. Like with winter weather, this association does not always play out the same way, but it does increase the probability of a wet summer.

For gardeners, both precipitation and temperatures play an important role in determining how well plants will grow. During El Niño, there may be less snow cover, which means less insulation for plants and greater potential for damage from the cold. Even though El Niño winters tend to be warmer than normal, that doesn’t mean there won’t be some cold stretches. The potential for less snow cover this year makes it especially important to protect vulnerable plants from winter damage. In addition, the lack of snow could result in less soil moisture recharge come spring. A melting snowpack can add beneficial soil moisture, especially during a gradual melt where the ground thaws as the snow is melting. However, less snow cover could reduce the potential for this extra soil moisture boost.

While many gardeners can utilize irrigation, adequate soil moisture and regular precipitation during the growing season makes everything a bit easier. With the winter outlook currently looking less snowy, the potential for a stormier summer may help to mitigate a drier start to the year. Frequent chances for storms during the growing season could help keep plants happy. While these storms can produce unwelcome side effects, like strong winds and hail, those phenomena are a risk every year, and whether you are impacted by a storm is largely luck of the draw.

In closing, here are a few important notes to remember about long-range forecasting. Unlike day-to-day forecasts, long-range forecasts, including those based on El Niño, should be thought of in simple terms. The outlook for a season can only indicate if it’s likely to be above, below, or normal in terms of temperature and precipitation. These broad trends are useful, but they don’t always tell the whole story. Consider that a single thunderstorm could produce more than an entire month’s worth of rain in a matter of hours. Technically, the month could therefore be wetter than normal, even if it only rained on one day. While that’s an extreme example, just keep in mind that long-range forecasts are general for a reason. The science of weather prediction continues to improve, but small-scale details still simply can’t be predicted months in advance. While El Niño is likely to bring certain trends next year, Mother Nature will no doubt have some curveballs in store.

FEATURED PHOTO: from S. Kehler /  NWS/NCEP Climate Prediction Centre