Published: Monday, October 23, 2017 @ 11:23 AM
By: Eric Elwell
— Up until today it may have been hard to realize that winter is now less than 60 days away. Our temperatures have been well above average for most of autumn with just a few brief cool spells.
This has led many people to believe that we are in for quite a payback for this nice weather this winter or we may be in for a quiet winter. Well, the outlook is in, and I wouldn’t count on an easy winter.
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First, let’s look at what will likely be the main players this winter. It is a term you have likely heard before and likely will hear a lot more of in the coming weeks. Yep, La Niña appears to be developing and there is up to a 65 percent chance it will hold or get stronger as we head into the winter.
Just a refresher, La Niña is a term given when sea surface temperatures across the equatorial Eastern Central Pacific Ocean are lower than normal by 3 to 5 degrees Celsius. Such a contrast in ocean water temperature has corresponding influences on the atmosphere and jet stream patterns across North America. Typically, during La Niña phases, the jet stream pattern across the southern half of the United States becomes very active, supplying lots of moisture across the region. The northern branch of the Jet Stream also can reach farther south and occasionally phase with the southern branch. This phasing can lead to a stormy weather pattern, especially across the Midwest, Great Lakes into New England.
Because of the development of La Niña, the forecast for the upcoming winter is for above normal precipitation across much of our region including right here in the Miami Valley. So now the question is, can we expect more snow than normal? The answer to this is a bit trickier, because while a more active southern jet stream can bring us more frequent and bigger storm systems, it can also bring warmer air farther north, leading more to a threat of heavy rain or ice.
Temperature patterns for this coming season will be dependent on several factors including how far north the southern branch of the jet stream can shift. But there are other key factors we will closely be monitoring which are a bit more difficult to predict beyond the short term. One of those is what we call the Arctic Oscillation. This has to do with the circulation patterns around the North Pole, more precisely known as the Northern Atlantic Oscillation (NAO) which more directly influences weather patterns across the eastern United States. During a negative phase of the NAO, westerly winds across Canada weaken, allowing arctic air to build in the region and get even colder. This cold air many times will get forced southward into the United States.
During La Niña years, there appears to be an impact on how far south intrusions of arctic air building in Canada can move. Because of our latitude here in the Miami Valley, we are still far enough north that we will likely see near normal temperatures, although it appears there will be times with the southern jet stream may send temperatures above normal.
Okay, so enough of the mumble-jumble meteorology stuff… here is the bottom line of what we are expecting.
First, thanks to above normal temperatures over the fall, water temperatures of the Great Lakes are also above normal. That will likely mean intense lake effect snows across the region. While we normally don’t have major snow squalls in the Miami Valley from Lake Effect Snow, the wind flow off of Lake Michigan can typically lead to light snow accumulations in the area and at times, lead to brief white-out squalls which are responsible for many of the winter weather related traffic accidents. It is important to note that with the recent warmth, any snowfall prior to December would likely melt quickly due to warm ground temperatures.
Using analog data to help in forecasting (looking at past years when fall conditions were similar to how they are now), our StormCenter 7 team believes our winter may be similar to that of the 2005-2006 winter. Just to refresh what happened that winter, we saw a quick, somewhat harsh start to winter followed by a mid-winter (January) warm-up. After a relatively quiet period, several big storms during the last month of winter brought a wintry mess across the region.
While this winter is expected to be busier than that of the last couple of winters, it likely will not be as extreme as the “polar vortex” winters we experienced a several years ago. If the current pattern remains similar to that of 2005, we will likely have a mid-winter break from any extreme cold before blasts of cold and snow return to wrap up the season. Stay tuned!
Eric Elwell is WHIO StormCenter 7 Chief Meteorologist. Contact him at firstname.lastname@example.org or follow him on Facebook and Twitter.