Mike's 14th Annual Winter Outlook
By Mike Goldberg, Meteorologist
Updated December 26, 2014
* A note to my faithful followers…
The last month or so has brought me several challenges which took a toll on my schedule and my research time. I apologize for the delay in getting my thoughts to you regarding the coming months. Keep in mind, winter hasn’t really started yet!
Each year when we discuss the upcoming winter and what we might expect, we talk about all the signals and patterns that the atmosphere offers. El Nino and La Nina (ENSO-the El Nino Southern Oscillation) seem to be the most popular topic, but there are a lot of other factors at work. This year, ENSO remains in a neutral state (which we typically refer to as “La Nada”), but the Climate Prediction Center says there is a 65% chance of an El Nino developing during the winter months. The North Atlantic Oscillation (NAO) is the next most popular signal, as it is what drives “blocking” patterns that can lead to cold and snow in the eastern United States. If you’re interested in more of the “science” behind the outlook, make sure to scroll down past the actual “forecast.”.
So let’s get right to it! Here’s what I’m thinking for the coming winter…
*** WINTER OUTLOOK 2014-2015 ***
DECEMBER (Average highs go from 55°F to 48°F, average lows from 35°F to 29°F)
Average Temp: 41.0°F
Temperatures: Above average (+1°F to +3°F) (continued up and down temperatures, but averaging a bit warmer than “normal”)
Precipitation: Average (several good storms with rain, not likely to see any widespread snow)
Average Snow (not a forecast): 2.1”
Highlights: Our trend of frequent “cold” shots continues. The month ends on a tranquil note.
JANUARY (Average highs in the mid to upper 40s, average lows in the upper 20s)
Average Temp: 37.9°F
Temperatures: Below average (-1°F to -3°F) (the cold spells grow more frequent and it should feel like typical mid-winter in central Virginia…some extremely cold weather possible during the second half of the month)
Precipitation: Slightly above average (best shot at a good snow event comes in mid to late January)
Average Snow (not a forecast): 3.9”
Highlights: Frequent cold spells with the possibility of some very cold days like last January. There’s certainly the potential for a sizeable snowstorm during the second half of the month.
FEBRUARY (Average highs go from 49°F to 55°F, average lows from 29°F to 33°F)
Average Temp: 40.9°F
Temperatures: Below average (-2°F to -3°F) (The extreme cold will back off, leading to more of a “normal” February)
Precipitation: Slightly above average (several winter weather events likely)
Average Snow (not a forecast): 3.4”
Highlights: More of the same. Some old-fashioned winter cold continues, with the possibility for numerous events that could bring snow or a wintry mix.
OVERALL (December/January/February combined)
Temperatures: Below average (While we start out close to “normal,” the cold takes over in January and February)
Precipitation: Slightly above average (A pretty “normal” winter in terms of precipitation and due to some very cold weather, snow and ice will certainly be a threat. However, it’s always important to note that cold doesn’t always mean a lot of snow)
SNOWFALL (yes, a forecast!)
The National Weather Service recently issued new 30-year climatic averages, incorporating the years of 1981-2010. The new snowfall “average” for Richmond is 10.3” inches, down a bit due to recent lean years. Predicting the amount of snow over the course of the entire winter is not easy. It’s an educated guess, based on the overall weather patterns that we expect. It’s important to remember that getting snow in central Virginia depends on all the ingredients coming together at the right time. If the cold air is in place but a storm isn't here, then it's a no-go. On the other hand, one big storm can give us our entire annual average in one day!
So here it is: We should be able to get at least “average” snowfall this winter in central Virginia. My "best guess" for the 2014-2015 winter in Richmond is 14 inches. This educated “guess” assumes we should be able to muster at least one good (significant) snowfall. I definitely think this winter will produce some very cold periods, which should give us decent snow chances. There is certainly the potential for more, but I’ve tempered “expectations” since a cold winter doesn’t always bring a lot of snow. Here are some estimates for potential snow throughout the region.
“Best Guess” Forecast Range
Richmond 14” 12”-16”
Petersburg 11” 9”-13”
Emporia 9” 7”-11”
Charlottesville 22” 20”-25”
Fredericksburg 18” 16”-20”
Reedville 9” 7”-11”
Williamsburg 11” 9”-13”
Norfolk 8” 6”-10”
Lynchburg 18” 16”-20”
MORE ABOUT THE OUTLOOK...
Predicting a season's weather in advance is never an easy task, and we sometimes have a hard time dealing with storms that are just a few days away. Scientific advances continue to give us more data and insight in order to provide a general outlook several months in advance. This helps provide valuable information that can be used by the public and businesses to plan appropriately for the weather that has an effect on their daily lives. Long-range forecasting of trends and weather patterns is known as climatology, or weather over an extended period of time. It is much different than the day-to-day weather we analyze and forecast on a daily basis. Now for more of the "science"...
EL NINO/LA NINA/LA NADA (ENSO)
El Nino is an abnormal warming of the surface water in the central and eastern Pacific Ocean. Its opposite is La Nina, and both affect pressure patterns over the Pacific, which in turn can bring changes in the weather for the United States and around the globe. The shifting pattern in the Pacific affects the placement of the jet stream, a band of strong winds in the upper atmosphere that directs the path of storms at the surface.
El Nino and La Nina are two modes of the El Nino Southern Oscillation (known as ENSO for short), which deals with the pressure and temperature patterns in the ocean and atmosphere in the tropical Pacific. When neither is apparent, the conditions are neutral and are usually referred to as La Nada. The Southern Oscillation Index (SOI) measures the pressure differences across the tropical Pacific from Tahiti to Darwin, Australia. ENSO is a key force in determining winter weather patterns over the United States.
** THE SITUATION NOW ** We remain in an ENSO neutral state (La Nada) right now. Recent trends suggest that an El Nino may develop over the winter, Even if it does, it would be relatively weak. Regardless, research has shown that while ENSO plays an important role in the winter weather pattern, there are many other factors that must be considered.
NORTH ATLANTIC OSCILLATION
Probably the most significant factor in determining winter weather on the East Coast is the North Atlantic Oscillation (NAO). This has to do with weather patterns in the North Atlantic and involves a flip-flop in the relative strength of pressure systems north to south over the open Atlantic. Normally, low pressure is located near Iceland (known as the Icelandic low) and high pressure sits just off of Portugal or the Azores (known as the Azores high). When these systems strengthen in these positions, a fast jet stream flow tends to drain cold air off of North America. This is the "positive" phase of the NAO and allows temperatures to moderate frequently over the Eastern U.S. and produces milder winters. If the NAO flip-flops, high pressure pushes north toward Greenland and low pressure develops farther south replacing the Azores high. The resulting "negative" phase of the NAO tends to produce harsh winter weather over Eastern North America. The high pressure over Greenland retards the passage of cold air, which then expands south over the Eastern U.S. Warmer sea surface temperatures over the North Atlantic help to encourage such a blocking pattern. This pattern is known as the "Greenland block," as the cold air is literally blocked from exiting the continent. The storm track is then suppressed south, and more snow often falls in the major metropolitan areas up and down I-95. These "blocks" are transitory by nature, but can repeat frequently and when this happens, we experience colder and snowier winters here in Virginia. In negative NAO years, the water tends to be warmer than normal in the tropical Atlantic and far North Atlantic, which it is right now.
** THE SITUATION NOW ** The NAO has trended more negative this year than the past few. Will this continue? It’s important to realize that the NAO goes back and forth frequently. It’s the longer term tendency that leads to more blocking patterns, which ultimately can mean colder and stormier days along the Eastern seaboard. It can sometimes be hard to maintain the negative NAO throughout the winter, and for snow lovers, we need storms at just the right time to “cash in.”
NEGATIVE NAO POSITIVE NAO
The Arctic Oscillation refers to opposing atmospheric pressure patterns in the northern middle and high latitudes. The oscillation is in its “negative” phase when relatively high pressure is over the polar regions and low pressure exists at the mid-latitudes (about 45 degrees north). The “positive” phase is when the pattern is reversed, and high pressure at the mid-latitudes drives storms farther north, while frigid winter air does not extend as far south into the middle of North America. This keeps much of the U.S. east of the Rockies warmer than average.
** THE SITUATION NOW ** The AO has also trended negative over the last several months, somewhat like our recent colder winters in 2009-10 and 2010-11. This trend could indicate a colder than “normal” winter is ahead.
POSITIVE PHASE NEGATIVE PHASE
PACIFIC DECADAL OSCILLATION
The Pacific Decadal Oscillation (PDO) is a large scale oscillation in the Pacific Basin that appears to relate to large scale thermohaline (both salinity and ocean temperature are factors) circulations that periodically speed up and slow down and control positions of the large warm and cool water pools in the ocean basin. This usually determines the mode of ENSO.
** THE SITUATION NOW ** The North Pacific right now is entrenched in the positive or “warm” phase, which supports a general western ridge/eastern trough pattern. This would also favor a colder than average winter in the East.
COOL PHASE WARM PHASE
The Quasi-biennial Oscillation (QBO) is an oscillation in the wind at 10-12 miles above the equator in the Pacific. This is an oscillation between easterly and westerly winds in a cycle that averages up to two years in length. Dr. Bill Gray, the famous hurricane forecaster, uses the state of the QBO to help determine the frequency of hurricanes in the yearly forecast. A westerly phase (or positive QBO) makes it less favorable for blocking patterns to set up. An easterly phase (or negative QBO) favors blocking patterns.
** THE SITUATION NOW ** The QBO has been running significantly negative, which favors blocking patterns, in turn favorable for supporting potential cold and stormy winter weather.
NORTH ATLANTIC SNOW COVER
Looking at snow cover across North America (mainly Canada) during the fall months can be a tell-tale sign of what's to come. When there is significant snow cover, arctic air masses have a breeding ground to expand and intensify, thereby making cold air outbreaks over the United States more significant and sustained. On the contrary, when snow cover is below average, these cold air masses have a tendency to modify before moving southward.
** THE SITUATION NOW ** The current snow cover across North America has been steadily growing. Recent research has shown that snow cover over Eurasia can be an even better signal as to our winter snow prospects. There, the snowpack got off to a record start, although it is not quite as impressive as of a month or two ago.
Soil moisture often plays a role in storm tracks and can be very helpful in seasonal outlooks.
** THE SITUATION NOW ** TSoil moisture has recently increased considerably along parts of the West Coast, due to numerous storms. However, significant dry conditions out West also supported the development of a western ridge, which has happened a bit over the past couple of months. This ridge development in turn favors trough development (and potential storminess) across the eastern U.S.
THE HURRICANE SEASON
There is not necessarily a correlation between the Atlantic hurricane season and the following winter's weather. However, a busy hurricane season usually is due to the pooling of very warm water throughout the Atlantic, often the North Atlantic. This can potentially have an effect on maintaining a negative NAO. This hurricane season was very quiet. However, I should note that this is similar to 2009-10, when we had a cold and rather snowy winter. Also, despite the lack of significant tropical activity, there are several critical areas of rather warm water (compared to “normal”) in the North Atlantic. Again, there’s not necessarily a correlation between the hurricane season and winter along the East Coast, but the pooling of very warm water in the north Atlantic could be a sign for more blocking to occur.
ANALOG YEARS/CLIMATE MODELS
The above are the major factors that are taken into account when making a long-range seasonal prediction. After examining what state these factors are in and will likely be in this winter, we usually look to find analog years where these conditions were similar and see what the resulting winter weather was like. I regularly review each factor’s history, taking into account individual analog years and their resulting weather conditions. There honestly weren’t any significant analog years that kept coming up, but I did find several years in recent memory that popped up (2002-03 was one of these).
We have many computer models (or simulations) of the atmosphere that are made up of thousands and thousands of mathematical equations. Current data from all over the world is plugged into these equations and a supercomputer quickly comes up with solutions that help predict the future state of the atmosphere and the resulting weather. There can be a wide variety of solutions and this is why you often hear different forecasts from varying sources. We all look at the same data, we just interpret it differently. Computer modeling of the atmosphere has come a long way over the last few years and we now have some very reliable climate models that can help predict seasonal trends and averages. In addition to daily computer model runs, we have models that help with seasonal forecasts called the Climate Forecast System model (or CFS).
You can see that the process of coming up with this winter outlook has been a very involved and complicated task. There are many factors that could easily change the impacts on our day-to-day weather and whether the outlook comes to fruition. The important thing is to be prepared and stay safe!