Winter decided to show up early this year. Officially, we picked up a trace of snow on Halloween to close out the month of October. November is also plotting to bring bouts of near-record cold so everyone wants to know… what does this mean for the upcoming 2019-20 winter season? This begins a chain reaction of questions in your mind. Will it be warm or cold? How much snow if any will fall? These are all great questions and ones I'll address in this discussion. You can always skip ahead to the end if you just want the summary. Look for the section titled "So, what do we think?"

Ask any meteorologist, when it comes to putting together a winter outlook, the very first thing to investigate is the current state as well as projected sea surface temperatures over the Eastern Equatorial Pacific known as ENSO. ENSO is one of the most important climate phenomena on Earth due to its ability to change the global atmospheric circulation, which in turn, influences temperature and precipitation across the globe.

Even though ENSO is a single climate phenomenon, it has three states, or phases, it can be in. The two opposite phases, “El Niño” and “La Niña,” refer to the warming and cooling of sea surface temperatures (SST), in the central and eastern tropical Pacific Ocean. Don’t forget about the third phase known as “Neutral” where tropical Pacific SSTs are generally close to average. It’s important because that’s what we are working with this season and ENSO-neutral conditions are expected to last into spring 2020.

In situations like this with receding drought and an ENSO-neutral forecast, you need to find answers in places you normally wouldn’t look. That place is the Bering Sea, Gulf of Alaska and coastal waters off the Pacific Northwest. In recent years, scientists began referring to unusually warm water in this area as “The Warm Blob” covering more than 600,000 square miles. You can clearly see "The Warm Blob" forming in this animation of weekly sea surface temperatures... 

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You may be wondering how ocean temperatures can affect the atmosphere. Well this is a perfect example of what's known as a teleconnection in the world of meteorology. Teleconnection patterns reflect large-scale changes in the atmospheric wave and jet stream patterns, and influence temperature, rainfall, storm tracks, and jet stream location/intensity over vast areas. Significant warming of the ocean creates a strong, persistent ridge of atmospheric high pressure over the northeastern Pacific Ocean…

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That in turn leads to a high amplitude pattern in the jet stream. So what does that mean for us? Well, we end up in the trough or dip in the jet stream allowing arctic air to spill into a large chunk of the country, including the Ohio Valley. While the bitter cold won’t be constant, it does favor below average temperatures.

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Looking out the window is the best way to tell what’s happening outside with the weather. You are probably thinking, “thanks captain obvious” but stay with me here. Before getting too caught up with what could happen, it’s important to examine what is currently unfolding. November 2019 is off to a chilly start and this happens to match up perfectly with November from 2013-14 and 2014-15. Why is this important? During those years, “The Warm Blob” was pronounced and we had ENSO-neutral conditions which is the exact situation we are in right now!      

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Let’s talk temperatures. Looking back at analogs for composite temperature anomalies during all of the ENSO-neutral years, it’s evident that a colder than average outcome is expected. Take a glance at the map below. The shades of blue/green indicate below average temperatures while the yellow/red colors represent above average temperatures…

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Remember that connection we made to the winter months of 2013-14 and 2014-15? This is really the main focus moving forward so don’t forget about “The Warm Blob” being pronounced and ENSO-neutral conditions. Our current situation with both is almost identical.  Analogs from those years also show colder than average conditions as well only making the case that much stronger…

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While on the subject, after looking at each month individually during what I’ll call the “connection winters” of 2013-14 and 2014-15, we found one interesting fact. December ended up with way above average temperatures! If the winter of 2019-20 follows the same path, then the cold may ease up in December.

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Don't get used to it. The cold then restocks and makes a return for January if the pattern follows the same path at our “connection winters” of the past. Remember, the lighter blue/green colors are implying temperatures below normal. The average high in Louisville bottoms out at 43 degrees so use that as a benchmark when looking at these maps. 

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February looks to offer up more of the same if you are still on board. The magnitude of the cold looks to intensify from the Great Lakes, down into the Ohio Valley. That would mean November, January and February all end up colder than normal with December being the only month that features warmer than average temperatures. 

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Now we can move on to precipitation. In order to do this we need to go through the same exercise as we did for temperatures, however, this time using analogs for composite precipitation anomalies during all of the ENSO-neutral years. For some reason, these color tables are completely opposite. The shades of blue/green indicate above average precipitation while the yellow/red colors represent below average precipitation. I’ll admit, it’s not the slam-dunk signal like we saw on the temperature side, but you can’t ignore the idea of above average precipitation in this pattern…

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We can finally address the last analog of the blog, I promise. Winter months from 2013-14 and 2014-15 don’t show a definitive signal either way. Bummer! That implies it should turn out to be close to normal if you take it verbatim. Based on the data, areas to our southwest would end up with below average precipitation…     

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So, what do we think

I want to begin by stating the obvious. Seasonal forecasts are not the most accurate thing we do because our weather models essentially become useless after 10 days out. In regard to temperatures, I have medium confidence in a "colder" than average winter. While the cold may back off during the month of December, it reloads and comes back with a vengeance for the rest of winter.

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Our confidence is much lower when it comes to precipitation. We’ve only been monitoring “The Warm Blob” for a decade so there’s hardly any climate data on its impacts. What we know is that the 2013-14 and 2014-15 “connection winter” seasons offered up 21.3” and 12.0” of snow respectively. Average those numbers out and you get 16.65”.  With that said, I think this year will be close to “normal to slightly above” when it comes to precipitation.  

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For reference, Louisville receives around 10 inches of rain and 12.5 inches of snow on average each winter season. As always, the WDRB weather team will be here for you every step of the way so please check back with us on a daily basis.    

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