PNA Positive, NAO Negative; What happens?

[Anonymous]

When the PNA is supposed to go positive and the NAO is supposed to go negative then what happens? Will philly finally get some snowfall?

[wxguy25]

the world comes to an end and philly gets no snow.

[AnthonyC]

This is what I know...

Positive PNA means ridge/warm in the west, cold/trough in the east.

Negative PNA means cold/trough in the west, warm/dry in the east.

Currently, there's a negative PNA...that's why Seattle had their first snowfall of the year. Latest forecasts suggest the PNA will be back to neutral...zonal flow...by Saturday of next weekend, then possibly becoming positive by early next week.

Anthony

[krysof]

funny, that would be rare considering the current pattern, but with Pna being positive meaning cold and negative nao means snow with the cold air and it could be a lot of it.

[donsutherland1]

Rodd321,

In general, a negative NAO/positive PNA pattern will prove snowier than other patterns in the Eastern U.S. However, there is considerable variability.

Seasonal Snowfall Averages for PNA+/NAO- (1950-51 through 2003-04):
Boston: 49.0"
Chicago: 43.5"
New York City: 30.3"
Philadelphia: 26.6"
Washington, DC: 21.3"

Seasonal Snowfall Averages for all other seasons (1950-51 through 2003-04):
Boston: 41.0"
Chicago: 40.9"
New York City: 22.9"
Philadelphia: 20.2"
Washington, DC: 15.4"

One great PNA+/NAO- Season: 1977-78:
Boston: 85.1"
Chicago: 82.3"
New York City: 50.7"
Philadelphia: 54.9"
Washington, DC: 22.7"

Worst PNA+/NAO- Season: 1997-98:
Boston: 25.6"
Chicago: 29.6"
New York City: 5.5"
Philadelphia: 0.8"
Washington, DC: 0.1"

Consequently, it is important to consider factors aside from the NAO and PNA in outlining what a season might have in store. In the case of 1997-98, an overpowering El Niño, particularly in Region 1+2, flooded North America with an unrelenting flow of unseasonably warm air.