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Although it is still midsummer, the team is beginning to turn their attention to the upcoming winter season. Allow the team to start off this forecast by talking about the previous winter season, and what “drove it” it to be so mild and snowless.
The largest problem for snow lovers last winter wasn’t only the La Nina, but rather the temperature of the stratosphere and the Madden Julian Oscillation (MJO). Most forecasters pay attention to the troposphere, but the team likes to account for as many variables as possible. So when the team looks at the stratosphere, the team observes that it is beginning to warm slowly as compared to last year when it reached record cold levels, promoting a very warm troposphere.
Things will be very different this year however, the stratosphere will be nice and toasty, creating ideal conditions for a cold lower atmosphere. This warming will also allow for features like the polar vortex, which is responsible for re-enforcing cold shots of air to sag further south, blanketing the eastern US in colder than average temperatures. This will also create significant high latitude blocking, keeping storms suppressed off of the east coast, some of which may develop into full blown Nor’ Easters, because of higher than normal sea surface temperature departures.
The Madden Julian Oscillation will be shunted into Octets 8-1. This is significant, because the MJO is a measure of pressures and temperatures over the Indian Ocean, which because of the amount of energy contained in that ocean control the global weather patterns. The El Nino that is strengthening will become west based driving (Left- an example of a west-based El-Nino in 2003) the MJO into a favorable pattern for pushing the moisture stream into the west coast, and may result in the formation of more storms. This oscillation will also balance the core of warmth over Alaska and Siberia, as compared to last year when it was incredibly cold and snowy and the east coast was kept into a ridge of higher pressure.
Given the aforementioned factors, This will translate into a ridge further west, mainly west of the Mississippi River, resulting in warmer than average temperatures, and below average precipitation, further worsening the drought situation. The far west coast, may have to deal with a consistent stream of weak to moderately strong storms which may dip further south. This potentially gives the southeast a better shot of ice storms as the jet stream sags further south delivering violent cold snaps and possibly threatening the orange crops throughout the winter. For the far southwest, you can expect typical El-Nino conditions, mild and wet weather, especially as the El-Nino strengthens.
At this point the upcoming winter looks colder and snowier than average (especially north of the Mason-Dixon line), which has actually been advertised on various climatic models including the CFS which has a proven track record.
A Look At The NAO /AO /PNA
Below the team gives a brief explanation on what certain pattern changes may be expected into the winter months. These changes range from the NAO, AO, and PNA.
Positive North Atlantic Oscillation (+NAO)
This is an unfavorable indicie for snowfall along the Eastern Coast. The jet stream will speed storms along it, bringing little snow, and the dominant Southwest Flow/Ridge will persist in this pattern bringing above normal temperatures to the East Coast.
Negative North Atlantic Oscillation (-NAO)
This is a favorable indice for above-average snowfall above the East Coast. The jet stream is more amplified and “digs” (moves) farther south, allowing storms to ride the jet stream up the coast. The high pressure is statistically weaker and farther offshore, and a dominant southwest flow will be very rare in this pattern.
Positive Arctic Oscillation (+AO)
This is an unfavorable indice for above-average snowfall above the East Coast. This keeps the Polar Vortex (massive low-pressure system that provides adequate supply of cold air up in Northern Canada.
The green arrows indicate that the Pacific Air is free to cross the United States due to the lack of blocking in the atmosphere.
Negative Arctic Oscillation (-AO) - This is a favorable indice for above-average snowfall above the East Coast. This is shown when the Polar Vortex had dropped South closer to the United States, and has provided low pressure systems enough cold air for a good snowstorm.
Positive PNA - This is a favorable indice for above-average snowfall above the East Coast. This indicates ridging (high-pressure) in the Western United States and troughing in the Eastern United Sates and places the jet stream so that Nor Easters can ride up the coast with the Jet Stream.
Negative PNA - This is an unfavorable indice for above-average snowfall above the East Coast. This indicates troughing (high-pressure) in the Western United States and ridging in the Eastern United Sates and places the jet stream so that low pressure systems are transported North of the East Coast.