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EPAWA 2015-2016 Winter Outlook

It’s that time of year that we look ahead to what the Winter of 2015-2016 will bring to our region. Some have asked why we wait until the 2nd week of November to release the Winter Outlook, but there is good reason for it. This year that is especially true, but waiting provides a much more accurate account of what to expect, and takes into account more recent observational data. 

We will break down the technical of observational data that contributes to this outlook, and for those less versed, an easy to understand breakdown of temperatures, precipitation, and snowfall in map form follows the technical discussion. We even have a breakdown of expected snowfall totals in a chart at the end of this outlook for 28 select cities and towns within our tri-state coverage area. 

For coverage during snow events and daily short, medium and long-range outlooks our Weather Forum has you covered. To learn more about our Weather Forum and all of our text messaging services, click here.

State of the ENSO and El Niño

Current Sea Surface Temperatures (SST) across the entire globe are shown below. This is the most critical factor in climate and long range forecasting. Although there are other factors, SSTs are most important because our planet is 70% water, and water temperatures and location of warm vs. colder pools of water drives the global climate. It is ultimately responsible for determining a warm and virtually snowless Winter or a very cold and wild snowy ride. The image below is a SST anomaly, which shows current SSTs in relation to what is considered to be normal vs. long term averages. The orange and red shadings indicate above normal SSTs, the blue and green indicate below normal departures.

sst

There are several areas that we are most concerned with. Most important is El Niño. This is the area shown above along the equator in the eastern Pacific Ocean. When waters are shown to be warmer than normal, it is an El Niño year. When they are cooler than normal, it is a La Niña year.

It has been well advertised that we are in an El Niño year. But it is not as simple as a strong Niño vs. moderate or weak. In this case, it is all about placement of the greatest warming in the equatorial eastern Pacific.

  • If the concentration of this warming is in the eastern Basins, which are the eastern half of Niño 3 and Niño 1+2, located between the coastal waters off of Peru (NW South America) and 120°W along the equator, that will lead to a warm Winter in our area.
  • If the concentration of this warming is centralized in Niño 3.4, located between 120°W and 165°W along the equator, that will generally lead to a snowy winter, especially if the focus is more west within Niño 3.4.
  • If the concentration of this warming is west based on either side of the International Dateline, that is most ideal for cold and snow in the east. This is the Niño 4 region.

Currently we favor the best warming based on the trends in trade winds and the Peruvian current to be farther to the west, generally west of 120°W for the upcoming Winter. This will make for a centralized El Niño, focused on the western half of the Niño 3.4 region.

elnino

The image above shows the recent evolution of El Niño and the regions of Niño that have seen the greatest rises and falls in Sea Surface Temperatures. Regions 1+2 have been cooling more rapidly than any other region farther west of it. Best tropical forcing is expected to continue to be in the vicinity of the International Dateline, which reinforces our projection for a west-centralized El Niño, one that would be more ideal for a snowy regime for Winter months. That image showing the best forcing is below:

Areas of projected best tropical forcing

tropicalforcing

Many have speculated that since we have a strong El Niño this year that it unanimously leads to a warm Winter… incorrect. Again, it is all about the placement of the greatest warming of El Niño in the equatorial Pacific. Below is a freely available graphic from the National Weather Service, showing the effects of a strong El Niño year vs. the other Winters in Philadelphia. Even with some years yielding next to nothing or nothing at all in the snowfall department, the composite average of those strong Niño years (6 of them) still show above normal snowfall:

elninowinters

Snow cover and the Arctic Oscillation

snowcover

Siberian snow cover during October-November has a correlation with the Arctic Oscillation. Research done by Judah Cohen has shown this correlation very well. The more expansive the snowfall is in Siberia the lower the temperatures get. This surface cooling creates a stronger temperature gradient across Asia. The jet stream strengthens across Eastern Asia which creates a pattern that favors poleward heat flux/vertical wave propagation that disrupts the strong polar vortex. This leads to a weaker vortex that is more susceptible to being split or displaced out of the arctic circle. This allows colder air to move into the Middle Latitudes.

The process of the vortex weakening and being displaced is what we call a negative Arctic Oscillation. The negative Arctic Oscillation allows the jet stream to bend far enough to the south to allow the cold air locked up in the northern latitudes to be displaced southward into our region.

The positive Arctic Oscillation keeps the cold air locked up to the north.

Snow cover over North America also plays a key role in our weather. The colder airmasses moving in will begin to modify much quicker over snow free areas. If these airmasses cross over snow cover they won’t moderate as much delivering a more powerful chill.

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Latest snowfall departures continue to show advancement across Asia.

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Snowfall anomalies over Northern Hemisphere for the month of October show similarities to the past 3 years. In addition, 2009 and 2002 also are above average.

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The Quasi-biennial Oscillaiton

QBO

A factor that also determines the strength of the vortex over the Polar regions is the Quasi-Biennial Oscillation (QBO). The stratosphere temperatures are very cold over the Arctic and warmer over the tropical stratosphere. This creates a strong thermal gradient and a strong Polar vortex. During a negative QBO the Brewer-Dobson Circulation is stronger and pumps more ozone from the tropical stratosphere to the polar stratosphere. This loosens the thermal gradient by more cooling taking place in the tropical stratosphere and warming in the polar stratosphere. This also makes it easier for the polar vortex to split or be displaced. In a positive QBO the gradient is strong and results in a stronger polar vortex.

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Latest values are strongly positive, and this is why we have been seeing a tendency for the Arctic Oscillation to remain positive as of late. However, in 2002 we saw a big drop toward neutral, which supported a cold winter with blocking. This also occurred but less dramatic in 1957-58 with a lot of blocking. In 1982-83 the QBO remained positive and we still saw a switch with some blocking in February, producing most of the snow that winter in the month of February.

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Tropical stratosphere showing warm anomalies have persisted across late Summer into Fall. Recently we see a dip slightly below the mean but the warmer temperatures are supported by the positive QBO.

The snow cover supports a negative Arctic Oscillation while the positive QBO currently does not. With the QBO already at such a high value it is reasonable to assume that we will be on a downward trend into winter. This is not a guarantee, as several positive phases have persisted with higher values for longer. But any drop in the QBO would support the poleward heat fluxes that can help weaken the vortex.

Another factor will be the El Niño. The Outgoing Longwave Radiation (OLR) has shown a focus right around the International Dateline. This is a favorable place for latent heat to be transported towards the Northeast Pacific, where the warm pool of water sits. This would favor heights building into Western Alaska and a weaker polar vortex. This would also make it possible for the vortex to be displaced along with the colder arctic air.

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The Madden-Julian Oscillation (MJO) and the effects of tropical forcing

The Madden-Julian Oscillation is an intra-seasonal variability in the tropical atmosphere. This is a measure of tropical convection and forcing along the equatorial Indian and Pacific Oceans. This convection, depending on where it is located and how strong the forcing is, can alter weather patterns downstream in our region.

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Phase 7 in January with the tropical forcing around the dateline.

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Phase 8 with the tropical forcing just east of the dateline.

If the current trends in the OLR anomalies continue we would likely see the pattern respond with a MJO phase 7-8 look. This favors the negative Arctic Oscillation, and a cold winter from January through March.

Analogs: comparing current year to past years

With regard to Sea Surface Temperatures, we can look at the big picture with the driving forces of El Niño and the Pacific Decadal Oscillation (PDO). The PDO is equally important, as we saw last Winter. The PDO phases of cold (negative) vs. warm (positive) determine a lot with how Winter unfolds along the east coast. The PDO is warm currently, and we can clearly see that we will once again be in a warm phase like last Winter….a text book warm phase. This shows the warm water piling up along the Western US coast extending up into Alaska and leads to a ridge over these locations. The PDO phases are shown below in the first image, immediately followed by a current snapshot of the SSTs in that region:

Cold vs. Warm PDO

PDO

Current SSTs and climate factors:

sst

The current SSTA map above points out a few major trends that could lead to an active winter:

  1. El Niño becoming focused in the central and western basins.
  2. Warm +PDO enhancing ridging in Western Canada.
  3. Cold pool of water north of Hawaii enhancing troughiness over or near Aleutians. This also ties in the forcing of the central-west based El Niño.
  4. Cold pool in North Atlantic. This SST configuration supports a -NAO set up.

 

So to match up past analogs, which are years where Sea Surface Temperatures are closest to matching the current year’s set-up, we compare to years of the past that are similar. We narrowed the list to 5 years, and weighted each year/season according to closest match. On the chart below, we outline the years that are the closest matches. You’ll take note that there is no 100% match to this year, but these seasons are ranked according to the closest match (1957-1958) to the least closest match on the list (1982-1983), and are weighted as such in rank order.

EPAWA Analog weighted rankENSOWarm +PDO?Above normal Northern Hemisphere snow cover?Total snow that fell in Allentown, PA
2015N/AStrong El NiñoStrong +PDOYes???
1957-1958#1Strong El NiñoSlight +PDO JFMN/A63.6"
2002-2003#2Moderate El NiñoStrong +PDOYes54.9"
1987-1988#3Moderate El NiñoModerate +PDONo40.2"
2009-2010#4Moderate El NiñoModerate +PDOYes75.2"
1982-1983#5Strong El NiñoSlight to Mod +PDONo 45.8"

Using the analogs above based on rank, the 5 seasons were weighted and ran through the NCDC analogs program. 1958 was weighted 5x, 2003 was weighted 4x, 1988 was weighted 3x, 2010 was weighted 2x, and 1983 was weighted once. Below is a snapshot of those combined analogs for January, February, and March.

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Jan, Feb, Mar using analogs: below normal temps

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Jan, Feb, Mar using analogs: above normal precip

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It is no surprise that the SST analog model has followed suit with the above with its latest projection… notice the warm areas (red) and cold areas (blue) match up to our analog choices that we blended above:

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Now it doesn’t take a degree in meteorology to figure out what that usually means when you combine below normal temperatures with above normal precipitation:  above normal snowfall. And most of those years didn’t disappoint. With that being said, we list our predictions for this year, the Winter of 2015-2016 below.

The official 2015-2016 EPAWA Winter Outlook Projections

Temperatures (month average)Precipitation (month average)Month Snowfall vs. Normal
December 2015Slightly above normal (+0.5°F to +1.5°F)Above normalNear to slightly above normal
January 2016Below normal (-1.0°F to -2.0°F)Near normalNear normal
February 2016Well below normal (-3.0°F to -5.0°F)Well above normalWell above normal
March 2016Slightly below normal (-0.5°F to -1.5°F)Slightly above normalSlightly above normal

Total snowfall December through March, as a percentage of normal

The active track promotes increase in coastal storms and more intense storms than last year as a whole. A battle zone may set up many times this Winter where split somewhere within our coverage area will be a tough rain/snow/ice line to deal with, making our job calling individual storms that much more difficult. Warm Atlantic Sea Surface Temperatures (SST) promote the notion of bigger coastal systems. But that could also lead to storms closer to the coast and more rain/mixing there, which would favor heavier snows falling inland. As winter progresses and the SSTs cool in the Atlantic, coastal tracks should be shifting more east. Conversely, far NW areas are less likely to get into big snow events, as the strongest lifting will be favored over the coastal plain. This will lead to a significant sinking motion in western portions of central PA and strong lifting in eastern PA and New Jersey. Naturally, mesoscale dynamics will change with each storm, and will be handled with much more accuracy in the short range. The balance between the two favor a snowy winter in the interior all the way to the coastal plain. The outlooks by month and as a whole are more weighted by location based on statistical probability.

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Select cities snowfall expectations within the EPAWA coverage area

Normal annual snowfall this locationEPAWA projected snowfall in 2015-2016
State College, PA46"57-69"
Mount Pocono, PA48"72-84"
Sussex, NJ41"61-72"
Williamsport, PA39"49-59"
Towanda, PA44"55-66"
Hazleton, PA44"66-77"
Pottsville, PA43"64-75"
Stroudsburg, PA39"58-68"
Harrisburg, PA33"49-58"
Hackettstown, NJ44"66-77"
Scranton/Wilkes-Barre, PA46"69-80"
York, PA25"37-44"
Allentown/Lehigh Valley, PA33"49-58"
Reading, PA32"48-56"
Lancaster, PA26"39-46"
Quakertown, PA31"46-54"
Pottstown, PA30"45-53"
Somerville, NJ30"45-53"
Newark, NJ25"37-44"
Wilmington, DE19"28-33"
Trenton, NJ23"34-40"
Philadelphia, PA22"33-39"
Freehold, NJ25"37-44"
Mount Holly, NJ20"30-35"
Dover, DE14"Greater than 24"
Vineland, NJ18"Greater than 31"
Atlantic City, NJ17"Greater than 30"
Cape May, NJ16"Greater than 28"

Winter Outlook Summary:

What can go wrong?

*There is also a possibility is the QBO does not fall from its current state, and stays strongly positive. This would increase the chances of the AO staying in a positive phase. However, given the El Nino becoming central based we are not that concerned even with a strong +QBO. 

*Blocking potential is not realized, lowering potential for a mega 2nd half of Winter, especially February. But as we mentioned above we think the transition to more blocking will occur. 

Although we listed several variables here, the odds favor our projected snowfall range estimates to be the most likely outcome.

Plain English summary:

 

  • In comparison to average, we expect most areas to feature well above normal snowfall, favoring eastern PA and especially SE areas
  • Winter starts off mild in December, colder in January, especially cold in February, slightly below in March. Despite the mild start in December, we expect a few cold shots to be timed with precipitation to allow for near or slightly above average December snowfall this year. The month to get out of dodge and plan an escape to the tropics would be February – very cold, well above normal snow.
  • Temperatures will not be as cold as they were last year as a whole, but will have some colder snaps, especially in the 2nd half of Winter
  • Less frequency of storms overall compared to last year, but when they do hit, they hold greater potential to produce larger amounts at one time – especially in the 2nd half of Winter
  • Greater potential for blocking unlike last year, making coastal storms slower, bigger, and more robust
  • Potential exists for higher amounts/ranges than listed if significant blocking develops

Please continue to follow the Facebook page for rapid updates as storms approach this Winter. The My Pocket Meteorologist™ text/email alert program allows you to receive text or email alerts sent directly to your phone or email specific to the county you live and/or work in. We also have our EPAWA premium forum which offers a comprehensive model analysis, discussion, and interaction with our team of meteorologists in advance of any Wintry threat this season. For more information on this successful program now in its 3rd year, please click on the My Pocket Meteorologist image below:

My Pocket Meteorologist Text/Email alerts and Premium Forum

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Forecasters:  Meteorologist Mike DeFino, Meteorologist Bobby Martrich

Premium Forum release: November 9th, 2015, 2:00pm
Updated for public release: November 13th, 2015, 6:00pm