In-Depth: Elements that help determine Winter Weather Outlook for 2019-2020

Weather Blog

(WPRI) — Southern New England winters can be a real roller coaster ride – ranging from bitter cold and excessive snow to mild and wet, with ice and sleet and everything else in between.

Last winter was not harsh with modest amounts of snow and near to slightly above average temperatures. So, what about this coming winter?

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Forecasting “specific” winter weather elements months in advance is difficult. However, today’s technology enables us to give a “broad general overview” of what the season may be like. For instance, will it be colder or milder than average? Dry or wetter/snowier?

Before we predict locally, we have to look globally, and with 70% of the earth covered in water, we start with one of the biggest driving factors (besides the sun) – the oceans.

THE OCEANS:

Our oceans hold and transport a tremendous amount of energy, which in term impacts global weather and climate. Quite simply, the energy from the oceans (among many other factors) can dictate how the winds (jet stream) circulates across the globe. The jet stream, in turn, determines the kind of weather we have.

We specifically look at “sea surface temperature anomalies” – where waters run colder and warmer than average. Some well-known ocean anomalies are called El Niño and La Niña. El Niño represents warmer waters in the equatorial Pacific while La Niña is a cooling phase.

This year, the waters in this specific part of the Pacific are near neutral. It appears some of the warmer waters have shifted further west. The location of these temperature anomalies is just as important. If we look at some winter seasons that feature this neutral state we see a tendency for more snow here. We can’t place the entire winter forecast on just this one factor, but it is one piece of the big global puzzle we look at.

BOTTOM LINE: No significant El Niño or La Niña this winter.

Next, we draw our attention to much warmer than average waters in the northern Pacific, just south of Alaska. I think this could be a big factor in the shape and location of the jet stream across Alaska and western Canada which would enable colder air to spill into the central and eastern United States.

Another area we look at is the water temperatures in the Indian Ocean. The phase is called IOD (Indian Ocean Dipole). For simplicity, we won’t get too involved with this other than to say it reflects where parts the Indian Ocean will alternately warm and cool. It’s yet another example of how ocean patterns on the other side of the globe can impact weather here in the United States.

Let’s not forget the Atlantic side of things, specifically the North Atlantic. The temperature anomalies here typically run on a 20-40 year cycle of warm vs. cool. The Atlantic anomalies are not nearly as frequent as the El Niño-La Niña cycle in the Pacific.

CANADIAN AND SIBERIAN SNOW COVERAGE:

Sea surface temperatures are not the only player. Autumn snow coverage, especially during October and early November, across the Canadian territories and as far away as Siberia is looked at. Studies have shown the areal coverage here can have a feedback influence on weather patterns across the Arctic circle.

BOTTOM LINE: Snow coverage this past autumn has been extensive which may favor more frequent patterns of cold for us.

Keep in mind, it doesn’t have to be extremely cold for snow. Sometimes all you need is “marginally” cold air coinciding with storms to still get snow. A milder than average winter doesn’t necessarily mean a warm rainy season. It can snow at a cold 27 degrees or a milder 33. Some storms start as accumulating snow only to turn to a mild rain, but at the end of the day, that “mild” storm has added on to the plus side of the Winter snow total.

THE POLAR VORTEX:

This feature has become well-known on social media during some winters. The polar vortex is an area of low pressure, a vast domain of spinning cold air across the North Pole. During winter, a “piece” of the vortex can sometimes break away and travel into the continental U.S. The result can be bitterly cold air. Back in January 2014, a piece of the polar vortex brought extreme cold to the U.S. Long-range predictions of the vortex are difficult to forecast. The polar vortex is not responsible for every cold outbreak but certainly the notable ones.

SOLAR ACTIVITY:

Just like our atmosphere, the sun goes through periodic cycles called solar MAX and solar MINS. It runs in a roughly 11-year cycle where the sun’s energy output fluctuates. We continue to be in a solar-min cycle (lower energy). Studies point to this phase favoring colder than average patterns here with some influence on the polar vortex mentioned above. There are other factors that can sometimes lessen the solar influence (like El Niño) – something we will continue to monitor.

BOTTOM LINE: Solar min may favor a more polar vortex influence and more frequent episodes of colder weather.

WINDS ABOVE THE EQUATOR:

The last global puzzle piece will look are changing wind patterns above the equator. We will keep this part simple. The QBO or “quasi-biennial oscillation” is a periodic change in wind speed and direction (west or east) high above the equator. These winds will eventually work down to the lower atmosphere over time which in turn can alter weather patterns.

After identifying the global factors in place now, we then look for past years (analogs) that had similar parameters in place and from there we make a general forecast of averages for the period December through March.

WINTER 2019-2020 OUTLOOK

Temperatures from December to March are forecast to be near to slightly below average, though there will moderations at times. December is expected to be seasonably cold with a slight edge towards a bit milder than normal. A more active storm track will bring above-average precipitation (both snow and rain).

The average snowfall for Providence each winter is around 35 inches, the northern part of the state a bit more and immediate coastal areas less. Snowfall outlook this winter is for normal to slightly above normal amounts.

BOTTOM LINE: A slightly colder, snowier winter than average. Compared to last winter it looks to be colder and snowier.

— Tony Petrarca

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