Mike's 13th Annual Winter Outlook
By Mike Goldberg, Meteorologist
November 26, 2013
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 is in a neutral state (which we typically refer to as “La Nada”), so the other signals take on even more importance. 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.”
When reviewing the data from the various signals and analyzing the potential developing patterns, we typically look for analog (similar) years to guide us. There are multiple analog years I came up with, but interesting enough the one that kept sticking out to me was one that to my knowledge, no other forecaster has mentioned so far. That is the winter of 1981-82. That winter was particularly cold in central Virginia and produced 21.2” of snow at RIC (ranking 22nd on the record of snowiest winters in Richmond). The majority of other analog years also tended towards colder than “normal” winters. However, snow is always the wild card even in cold winters. That’s because cold air is typically very dry air, so very cold winters can end up producing below average snowfall. That being said, since 1981-82 is sticking out to me, I have leaned in its direction, but tempered the cold and snow a bit.
So let’s get right to it! Here’s what I’m thinking for the coming winter…
*** WINTER OUTLOOK 2013-2014 ***
DECEMBER (Average highs go from 55°F to 48°F, average lows from 35°F to 29°F)
Average Temp: 41.0°F
Temperatures: Below to much below average (-2°F to -4°F) (a few warmer spells, but for the most part a cold start to winter)
Precipitation: Average (several storms have the potential to produce some snow)
Average Snow (not a forecast): 2.1”
Highlights: The trend that produced cold spells in November continues and we certainly could be looking at some snow. I don’t think we’ll see a “big” snow in December, but the ground could turn white one or two times!
JANUARY (Average highs in the mid to upper 40s, average lows in the upper 20s)
Average Temp: 37.9°F
Temperatures: Below average (-2°F to -3°F) (the cold continues, and mid-January could produce an extremely cold week with temperatures in the 20s and 30s for highs)
Precipitation: Average (a pretty good shot at a decent snowfall, particularly in mid to late January)
Average Snow (not a forecast): 3.9”
Highlights: A very cold month by recent standards. A milder stretch (the typical January thaw) could begin the month, but don’t be fooled. Overall it will be cold with a good chance for at least some snow and possibly a sizeable event!
FEBRUARY (Average highs go from 49°F to 55°F, average lows from 29°F to 33°F)
Average Temp: 40.9°F
Temperatures: Slightly above average (0°F to 1°F) (The extreme cold will back off, leading to more of a “normal” February)
Precipitation: Slightly above average (a wetter month, with an active pattern…could be a winter weather event to close the winter)
Average Snow (not a forecast): 3.4”
Highlights: A trend to somewhat “milder” conditions to finish the winter. However, one last blast is possible and I wouldn’t rule out snow in late February/early March.
OVERALL (December/January/February combined)
Temperatures: Below average (Extreme swings are possible with the cold outdoing the milder periods, particularly in December and January)
Precipitation: Average (The very cold weather may produce more dry spells, but precipitation should be on the uptick getting closer to average. That trend will continue going above average in February)
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 2013-2014 winter in Richmond is 15 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. Here are some estimates for potential snow throughout the region.
“Best Guess” Forecast Range
Richmond 15” 13”-17”
Petersburg 12” 10”-14”
Emporia 10” 8”-12”
Charlottesville 24” 21”-27”
Fredericksburg 19” 16”-22”
Reedville 11” 9”-13”
Williamsburg 11” 9”-13”
Norfolk 9” 7”-11”
Lynchburg 21” 17”-23”
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’re clearly in a La Nada period (neither El Nino or La Nina). There are signs that an El Nino may eventually start to develop, but that won’t happen until after the winter. Interestingly enough, the winter of 1981-82 was rather similar regarding ENSO. Even so, with no clear signal, other factors will likely play an important role in what takes shape this winter.
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 tended more positive the last two winters, after being predominately negative for the colder and snowier winters of 2009-10 and 2010-11. The NAO took a turn to negative in October. Will this be a trend? Back in 1981-82, the NAO had been more positive through the middle of the year, took a turn to negative in September and stayed that way through the winter. We’ll see if that happens this year. 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
ARCTIC OSCILLATION (AO)
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 turned from negative in September to positive during October. However, it’s yet to be seen whether this will turn into a trend. A signal during the fall months doesn’t necessarily hold throughout the winter.
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 generally in the negative or “cool” phase, which tends to support cooler and stormier weather for the West Coast. This is not a good sign for East Coast snow lovers. However, I should note that we had a negative PDO during the 2010-11 season, yet still had a colder than average winter in the East, Also of note was a slight trend “up” in September, but we went “down” a bit again in October. If the PDO can turn back to the “positive” trend, colder weather could be ahead.
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 positive for several months, but that positive signal is weakening a bit as of October. The positive phase favors non-blocking patterns, so winter fans need the trend to continue.
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 is more extensive this November. Recent research has shown that snow cover over Eurasia can be an even better signal as to our winter snow prospects. There, the snowpack is looking quite significant.
Soil moisture often plays a role in storm tracks and can be very helpful in seasonal outlooks.
** THE SITUATION NOW ** The long-term Palmer Drought Severity Index map below shows dry conditions exist out west. This could favor ridge development, which would then tend towards 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 season was rather sparse in terms of coverage. 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 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 have specifically gone back and followed each factor’s history, taking into account individual analog years and their resulting weather conditions. I considered several analog years (each based on different combinations of comparable signals), some more significant than others (2012-13, 2006-07, 2001-02, 2000-01, 1996-97, 1981-82 and 1970-71). These winters varied quite a bit, but the one analog that sticks out to me is 1981-82 and as I mentioned, that was a particularly cold winter in central Virginia. Since there is some conflicting evidence from some of the signals, I have “tempered” the outlook so it’s not as harsh as the winter of 1981-82.
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. The Climate Forecast System model (or CFS) has not been all that consistent over the last few months, but has trended in a “cooler” direction for us.
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!