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Recently, a lot of people have been asking me "Where's all our snow?!" In this discussion I'll explain why Ridley Park has been so warm, and if there is any hope for snow in the coming weeks. 

 

Ridley Park and most of the country has been so warm because of many factors but there are special signals that meteorologists use to determine what the general pattern of the atmosphere that are called Teleconnections. Teleconnections are states of the atmosphere that serve as the "governing factors" and determine essentially wether we get a rainy pattern or a snowy pattern. I won't get into the details and the confusing science behind it, but I'll provide a clear explanation of what these are. 

 

There are four main teleconnections that are the most influential to this area, and those (in order of significance) are the:

 

  • El-Nino Southern Oscillation (ENSO)
  • North Atlantic Oscillation (NAO)
  • Arctic Oscillation (AO)
  • Pacific North American/Pattern (PNA)

 

The El-Nino Southern Oscillation has two phases, La Nina and El Nino.

 

La Nina- When we are in a La Nina phase (which we are in a weak one now) colder than normal waters are in the equatorial Eastern Central Pacific Ocean. The waters enhance the northern jet stream or polar jetstream (jetstream meaning an area of fast moving west to east winds in the high altitudes of the troposphere). This correlates into a colder and wetter than normal over the Northern United States and warmer and drier usually over the Southeast United States. 

 

El Nino- When the waters are warmer than normal waters in the Eastern Central Pacific Ocean (especially near the equator), the waters enhance the southern jetstream. That correlates into wetter than normal and cooler than normal for the east and Southeast and warmer than normal and drier over the Northern United States. 

 

Following that, the NAO is a teleconnection that has to deal with the position of a big area of high-pressure near Greenland. If the high is over Greenland that means that the storm tracks are suppressed to the south and also keeps the cold air locked in near Greenland and also keeps the cold air locked in here. It is also a huge stop sign in the atmosphere and forces the storms to intensify off of the New Jersey/New York coasts, rather than intensify farther north. For cold and snow, we have a better chance of seeing significant storms that bring snow to our area if the NAO is in a "negative phase".

 

When the NAO is in a "positive phase", a low pressure is over Greenland, and allows the  storms to track over land, and does not lock the cold air in. The storms also are quicker moving and are generally warmer. Almost all of winter the NAO has been positive, hence the reason why we have only had .5" of snow for the year. 

 

The recent Model guidance has the NAO trending positive during the last half of January, but trending towards neutral/negative for the start of February.

 

Link:http://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/nao.sprd2.gif

 

 

Next up is the Arctic Oscillation. The Arctic Oscillation measures the amount of cold air that is available for storms to tap into. When the AO is positive the surface pressure in the polar regions is low, thus keeping the cold air locked in the Arctic, not here. When the AO is negative, there is high pressure in the Polar region, forcing the cold air down from the poles, and making it more readily available for storms that travel near our area to be on the snowier side. 

 

The AO has been positive for the majority of this winter, hence the reason why the average temperature for November, December, and the first half of January to be above average. Recent models have the AO staying positive, but falling towards neutral (+-0) for the start of Febuary. 

Link: http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/...

 

 

 

The fourth significant teleconnection is the PNA. The PNA is influenced by another teleconnection called the Madden-Juilian Oscillation and that just basically determines where the troughing (low pressure systems) and ridging (high-pressure systems) are in the world. The PNA tells us wether there is a ridge in the west and a trough in the east, a trough in the west and a ridge in the east. You might ask "What is so significant about that?". Well, when the PNA is positive, there is a ridge in the west bringing them warmth, and our area is stuck in a cold, arctic trough. When the PNA is negative, the west gets the trough that brings them cold, and the east gets the warmth influenced by the ridge. 

 

For the majority of the winter, the PNA has been positive as seen below by this chart, but is heading negative, spelling warmth for the Eastern United States until the beginning of February. 

Link:http://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/pna.sprd2.gif

 

So what does February bring? The recent data suggests (this data can change at any time) that the last half of January will be warmer than average. It also shows the NAO and the AO starting to go neutral and then slightly negative by the time February rolls around, which may make for a colder/snowier February.

 


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