WDRB 2017-18 WINTER OUTLOOK: Temperature & Precipitation Predictions...
Hate it or love it, the upcoming 2017-18 winter season seems to be the talk of the town right now. What can we expect this winter? 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.
I feel as meteorologists we often lose sight of the actual atmospheric signals because we are so focused on the dozens of different indicators. These indicators include such things as the current state and projected sea surface temperatures over the Eastern Equatorial Pacific (known as El Nino/La Nina), the tropical 30-60 day oscillation known as the Madden Julian Oscillation (MJO), the North Atlantic Oscillation (NAO), the Pacific North Amercian Oscillation (PNO) and current climatological trends. Among these indicators, the most important are the forecasted state of El Nino/La Nina and current climate trends.
La Nina is characterized by unusually cold ocean temperatures in the Eastern Equatorial Pacific, compared to El Nino, which is characterized by unusually warm ocean temperatures in the Equatorial Pacific. Currently, the Eastern Equatorial Pacific is experiencing cooler than normal sea surface temps (SST) off the coast of South America on the order of a degree or two below average. All of that blue showing up off the coast of South America tells us the water is cooling and suggests a weak La Nina is developing...
Image Credit: NOAA
Taking a look down the road, the dynamical model averages of the IRI/CPC plume favor a weak La Niña. I know the map below can look confusing, but I want you to focus on the bold yellow line. It's the average of all the computer models. Sea surface temperatures are on the y-axis and time is on the x-axis. Notice how it is below the 0 degree meaning the La Nina should hold through winter...
If the only thing you took into account was the current state of this oscillation, it would lead you to believe a "wetter" (precipitation) and "warmer" (temperature) winter should unfold for the 2017-18 season. Check out the map below and notice the wet and warm signal over the Ohio Valley...
Image Credit: NOAA
Here's the problem. If the La Nina was going to be strong then I would end this here and call it a day. Unfortunately, when the state of El Nino/La Nina is weak or neutral, then other factors can come into play. Let's talk about what's been going on lately to get a better grasp of the situation. We've been in what's referred to as a "high amplitude" pattern with many ups and downs in the temperature department. The NCEP CFS 2-m temperature map shows crazy amounts of cold collecting in Canada through the middle of December...
Image Credit: WeatherBell
If you look closer, notice that we are in between the above and below average temperature anomalies. This puts us in a "baroclinic zone" which is a region where a sharp a temperature gradient exists. Storms have a tendency to ride these zones leading me to believe we will experience an active storm season. That will have a direct impact on temperatures meaning we will probably see temperature extremes this winter. If a low pressure can gain enough strength, warmth will get pulled up ahead of it with much colder air rushing in behind it.
Another thing to consider is whether or not "The Blob" exists. "The Blob" is an anomalously warm area of SST's in the North Pacific that can lead to upper atmospheric ridging over parts of the Bering Sea and Alaska. A ridge at this latitude would also "split" the jet stream into a Southern Branch over the Pacific and a Northern Branch that would theoretically extend well north of the Arctic Circle perhaps setting up a "Cross-Polar Flow"...
This pattern would lead to severe arctic intrusions into the Eastern US at times this winter. We've been keeping a close eye on the SST's in the North Pacific lately. During the middle of October, warm water dominated this zone...
Then a typhoon, formerly known as Lan, recurved out to sea after hitting Japan. It caused massive amount of upwelling which is a process in which deep, cold water rises toward the surface. Look at the difference in SST's by the end of October...
The waters are now slowly modifying and trending back to the way they were, but it's tough to say exactly where they go from here. If the warmth continues to build back, and I think it will, then it will reinforce the classic La Nina winter pattern...
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. Without some sort of strong climate signal to work with, predictability can suffer significantly.
For reference, Louisville receives around 10 inches of rain and 12.5 inches of snow on average each winter season. I have high confidence in a "wetter" than average winter since we are right in the battle ground for storms. If I had to put numbers out there, I would say 10 - 15" of snow is possible, but this is nothing more than an educated guess. Our area is notorious for being on the freezing line when storms enter the picture. In these cases, we tend to deal with the wintry mix of freezing rain, sleet, snow and rain most of the time. This may be a common theme early in the season and here's why. In regard to temperatures, I think winter will start off warmer, then make a move colder during the second half of the season. As a result, snow lovers may need to pack some patience. Also, it will be tough to make up for lost time so we could end up with a "warmer" than normal season as well. However, my confidence is much lower in regard to the temperature outlook. Instead, the take home message should be that we need to prepare for temperature extremes. I like to refer to this as temperature tug-of-war. We will probably flip back and forth between mild air and bitter cold rather than prolonged episodes of either one. 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.
-Rick DeLuca
The Best Team ever.
Posted by: Jeffery Kolling, Jr | 11/06/2017 at 08:00 PM
in other words it's winter time and take what ya get!
Posted by: louis peterson | 11/06/2017 at 08:54 PM