PRELIMINARY WINTER OUTLOOK 2017/18 Joseph D Aleo, WeatherBell Analytics Seasonal forecasting is challenge for many reasons. There are many drivers that influence winters. When they synchronize, forecasters can have a higher confidence in the forecast outcome. When different factors suggest very different results or if a factor or two change after you made the forecast, so might the outcome. Also when there is a lot of in season variability the pattern that dominated longest and strongest will dominate. Sportscasters and we sports fans know how difficult it is to predict ahead of the season how their home teams will do. Like in the atmosphere, the players change year to year and we wonder how the new players will fit in. Then there are the inevitable injuries sometimes to key players, which like the changing factors in the atmosphere ocean that can lead to a disappointing or at least a different than expected result. At WeatherBELL, we use 25 factors in our statistical model we call the Pioneer Model mostly relating to ocean, solar and certain atmospheric conditions. El Nino and La Nina are heavily represented. Forecasters have used that since their global influence was proven in the late 1980s. These tropical ocean events come in different flavors though which has to be considered. But even when El Ninos and La Ninas are not happening, other ocean warm and cold pools, solar activity and features in the atmosphere sometimes very far away can tell us a lot about the likely dominant winter patterns. I started down this path when I was the first Director of Meteorology at The Weather ChanneI. In that capacity, I was fortunate to get to know Jerome Namias, the first Director of the Long Range Forecasting Branch (long range then was 5 days!) of the US Weather Bureau (now NWS) in the 1950s and later chief scientist at Scripps. He later wrote about how warm and cold pools in the oceans can anchor the jet stream, and since they only slowly change, they can help us forecast months into the future. He documented in a 1977 paper what later became known as the Great Pacific Climate Shift when Pacific warm and cold ocean pools of water
literally flipped and we transitioned from the La Ninas of the early 1970s, to the frigid weak El Nino winter of the late 1970s. Two decades later, fishery scientists at the university of Washington trying to explain why salmon production change dramatically in cycles of multiple decades confirmed the flip- flop pattern in ocean temperatures they called the Pacific Decadal Oscillation (PDO). The PDO we found not only affected the Salmon populations, but affected the weather in North America and tilted the scales towards El Nino or La Nina. See how these factors and other drove the winters of 2013/14, 2014/15 and provided special challenges in 2015/16 and 2016/17. We pay special attention to the incredible winter of 2014/15.
2013/14 WINTER When the water turned warm in the northern Pacific in 2013 like in 1976 and the other harsh winter years like 1916/17, 1917/18, 1995/96 and 2002/03, our statistical Pioneer Model began predicting a very cold winter for the Great Lakes and east. Joe Bastardi and I called for a potential historic winter starting in the summer. This drove the Pioneer model to predict the 'Polar Vortex' pattern. Chicago had its coldest December to March on record since 1872 and second snowiest. Detroit had its snowiest.
2014/15 WINTER The following year had that ocean warm pool again and other warm and cold pools that agreed on a cold east winter. The El Nino was a central Pacific one called the El Nino Modoki. The weak Modoki years were cold El Ninos,
Pioneer got the cold east including southeast Canada right but was not warm enough in the southwest (few analogs had that much warm water all along the west coast). For the 10 northeast states and DC it was the coldest January to March on record. 2013/14 had been 11 th coldest since 1895.
In Boston, February 2105 was the second coldest month behind only February 1934. No date reached 40F and 14 days had lows 10F or lower. It was the coldest January to March in Hartford, Providence and Worcester and the third coldest in the longer history Boston data.
It was the snowiest winter in Boston on record beating out 1995/96. In the 39 days in the heart of 2014/15 winter, when Boston had 100.2 inches of snow, the melted precipitation was 5.69 inches, a ratio of 17.6 to 1. Typical snow to melted precipitation ratio is 10 to 1 here near the coast. The big snows in that winter and most recent snowy years have come with unusually cold temperatures. Seasonal snows are high in cold winters, low in warmer winters.
2015/16 SUPER EL NINO Then came the super El Nino of 2015/16. The strong El Nino suggested a warm winter but other SSTA pools said cold. It was also an anomalous strong El Nino because the warmest water relative to normal was west of south America around 120W. Most super El Ninos have the largest anomalies near South America. It was still more of a strong warm Nino.
Pioneer and the CPC CA statistical model had a cold southeast. After a toasty warm December the expected cold was there in most of January with a record blizzard and reappeared on Valentine's Day, when Boston and Providence plunged to - 9F.
But after that blast, winter ended warm again. The bookend El Nino warmth dominated and the forecast busted.
2016/17 WINTER The SSTA pattern in 2016/17 showed a La Nina that faded to La Nada. There was still residual warmth in the northeast Gulf of Alaska. However with a strong jet stream feeding off deep snow in a band in Siberia, the water off Alaska turned cold there by early winter. We also saw one of the key elements in low solar years, the Quasi Biennial Oscillation of QBO (to be discussed in the 2017/18 section), failed to establish the easterly mode in the tropical stratosphere for the first time in the record. These changing factors took away chances of a rebound cold winter by favoring more ridging in the south and limited high latitude high pressure blocking. The borderline weak La Nina state favored a lot of winter variability, which verified but with warmth dominating except in all but the northwest.
2017/18 WINTER As we head towards the winter, we have another weak La Nina (the cold water along the equator extending west off South America on the image below). This year has colder conditions than 2016/17 but notice the confused ocean temperature pattern elsewhere.
Our model, which weighs the factors focuses on other factors. In the late 1980s and early 1990s, NOAA s Climate Prediction Center researchers found the winds that blow 10-12 miles high over the equator (called the Quasi- Biennal Oscillation or QBO) flips between west and east about every 13 or so months, and alters the patterns with El Nino and La Nina and what happens in years during active and quiet sun winters. Last year was a weak La Nina. The QBO surprised the meteorological world by failing to complete its normal easterly transition. The westerly phase resumed. This supported a cold western North America and polar region and a strong warm southeast U.S. ridge (left below). This year, with an easterly QBO coming on strong, the research suggests a cold west and north (right just below) with suppressed southeast La Nina warmth. It favors warmth near the pole which you may be surprised to hear makes it colder in mid latitudes. Last year and this we are in a quiet sun phase. For 2017/18, the east QBO, low solar years are very similar to the easterly QBO La Ninas.
When the polar region is warmer with high pressure, cold air arctic is deflected south, and the jet stream buckles into a Meridional flow (right below). When the polar region is cold, the vortex is contracted the flow tends to be more zonal and the weather warmer in North America and Eurasia as the west winds carry maritime air inland (left below). This cycle is called the Arctic Oscillation or AO. See next how the negative AO (right side in the maps above) makes all ENSO states colder (bottom maps below).
The Pioneer model has a mix of La Nina and La Nada winters as analogs (most similar years) this year and with the east QBO and low solar is cold a lot like a blend of the bottom left two maps just above. November to January Temperature Anomalies
HOW ABOUT SNOWFALL? October storms like we the big one we just had can provide a clue to storms in the winter. Remember in 2012 after Sandy we had a Halloween snowstorm and two more big ones later. Also we warn, La Ninas often have cold highs moving through southern Canada, which can lead to early winter ice storms as in 2008, 2011 and back many years in December 1973 when I was just starting my career at WCBS in New York City.. When there is more high latitude high pressure (we call them blocks) as in 1995/96, the southeast ridge and storm track is suppressed. That was a record snow winter, exceeded only by 2014/15. Joe Bastardi s WeatherBELL consensus snow forecast calls for another snowy winter. See how we had 25 NESIS (we used to call them Kocin storms) the last 10 years. No prior 10- year period had more than 10.
And Boston s 10- year running mean is the highest in the record back to the 1880s. Will this trend continue? We will update as needed if factors change on WeatherBELL.