Mike Goldberg
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Mike's Winter Outlook


Mike's 15th Annual Winter Outlook

By Mike Goldberg, Meteorologist
November 30, 2015



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) always seem to be the most talked about.  This year, El Nino is clearly the most dominant player, as it could end up being the strongest on record.  The Climate Prediction Center expects El Nino to remain strong through the winter.  The North Atlantic Oscillation (NAO) is typically the next most popular signal, as it is what drives “blocking” patterns that can lead to cold and snow in the eastern United States.  However, there are several other key factors discussed below, along with comparisons to previous winters in the “science” behind the outlook.

For those that don’t want to read too much and just want the nuts and bolts, here’s what I’m thinking for the coming winter…

*** WINTER OUTLOOK 2015-2016 ***

GENERAL THOUGHTS:  Wet & mild, better chances that one snowfall gives us most of our seasonal total than numerous storms…so chances favor below average snow in Richmond, but above average possible over the mountains to the west!

DECEMBER (Average highs go from 55°F to 48°F, average lows from 35°F to 29°F)

Average Temp:       41.0°F
Forecast:                44.2°F

Temperatures:  Well above average (+2°F to +4°F) (averaging warm, but a few cold spells)

Precipitation: 
Above average (several good storms with mainly rain, might see a mix if the timing is right…not likely to see any widespread snow)

Our average snow in December (not a forecast):       2.1”

Highlights:  A warm (potentially very warm) month overall, but with a few brief cold spells. 
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JANUARY (Average highs in the mid to upper 40s, average lows in the upper 20s)

Average Temp:       37.9°F
Forecast:                38.9°F

Temperatures: 
Near to above average (0°F to +2°F) (Overall a bit cooler, but still near average much of the time)

Precipitation: 
Slightly above average (Still a bunch of storms, likely to be wet with some ice and snow possible)

Our average snow in January (not a forecast):       3.9”

Highlights: While there may be some wintry weather, overall cool and wet at times.  If the timing is right, maybe a snow event.

FEBRUARY (Average highs go from 49°F to 55°F, average lows from 29°F to 33°F)

Average Temp:       40.9°F
Forecast:                42.0°F

Temperatures: 
Near to above average (0°F to +2°F) (While coming out near or a bit above average, a spell of very cold weather possible, particularly in the first half of the month)

Precipitation: 
Above average (We could see numerous storms, with our best shot at seeing a decent snowstorm)

Our average snow in February (not a forecast):       3.4”

Highlights:  Best shot of a significant cold spell of 7-10 days.  Therefore, the best shot at seeing a snowstorm.  This could very well amount to most of our seasonal snowfall.
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OVERALL (December/January/February combined)

Temperatures: 
Above average (Some very warm weather at times, especially during the beginning of winter)

Precipitation: 
Above average (A wet winter, with most systems producing rain or a mix.  One good snow is a distinct possibility, especially during early to mid 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:  While it’s not likely we come in above average, I have to account for the possibility of one big snow, which has been a factor in several significant El Nino years.  One storm can give us most of our seasonal snowfall in Richmond (all of central and eastern Virginia included), and this is probably the case this season.  Keep that in mind with this outlook, because there’s a pretty good chance we end up with very little snow if we don’t get the necessary ingredients to come together at the right time.  I don’t think this is a year that we have numerous snow events, so we’re relying on a good one here!  Here are some estimates for potential snow throughout the region.

                           “Best Guess”        Forecast Range

Richmond                 10”                         8”-12”
Petersburg                8”                          6”-10”
Emporia                     7”                          5”-9”
Charlottesville         17”                        14”-20”
Fredericksburg        12”                        10”-14”
Reedville                   7”                           5”-9”                          
Williamsburg             8”                           6”-10”
Norfolk                      6”                           4”-8”
Lynchburg                14”                        12”-16”

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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"...

THE FACTORS

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 ** Big time El Nino!  Recent trends show El Nino strengthening rapidly and this could end up the strongest on record (on par with 1982-83 and 1997-98). This will be the major player in the overall winter pattern.  It is likely to frequently flood much of the lower 48 with mild air during December.  Other factors may reverse this trend later in the 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 is trending positive, not good for snow lovers!  However, 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. However, a brief spell of a negative NAO may be all we need for a decent snowstorm, IF it happens at the right time! 

                                  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 has been trending positive, which further supports milder conditions here.  However, there are significant similarities to the 1982-83 winter here, and that year went negative in February, leading to a big snowstorm!


                 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.  However, there are also signs of some slight weakening.

                       COOL PHASE                                                                          WARM PHASE


QUASI-BIENNIAL OSCILLATION

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 positive, which does not favor blocking patterns and in turn prolonged cold spells.  This was also the case in 1982-83, when we eventually had the big February snow.  

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 not necessarily impressive.  However, recent research has shown that snow cover over Eurasia can be an even better signal as to our winter snow prospects.  Like the last few years, this has been running above average during the fall months. 

SOIL MOISTURE

Soil moisture often plays a role in storm tracks and can be very helpful in seasonal outlooks.

** THE SITUATION NOW ** Soil moisture has recently increased along parts of the West Coast.  We’ve seen significant moisture across the south, due to recent storm tracks. This trend continues to favor stormy weather at times heading into the winter season. 

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.  There is a pool of rather warm water off the Northeast coast.  There is 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 potential 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. 

The strong El Nino led to consideration of similar events in the past.  That brought me to the following winter seasons, which have shown great variability in Richmond snowfall (listed in parentheses).
1957-58 (20.5”)
1965-66 (29.2”)
1972-73 (6.7”)
1982-83 (29.4”)
1997-98 (1.2”)

The two strongest El Ninos were 1982-83 and 1997-98.  The first produced one of our top 10 years for snow (mainly due to a big February snow).  The second produced one of the leanest years! 

After careful consideration of other factors, it would appear the 1982-83 is a slightly better comparison than 1997-98.  However, there are some distinct similarities to the latter.  Keep in mind that while the winter of 1982-83 produced the big snow amount, it also had quite a bit of mild weather.  So once again, we’re really looking at a situation where we have to rely on one big storm to give us a high snow total, as opposed to multiple smaller storms.

We also 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!

-Mike
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