Going Negative

To hear some people tell it...winter just ain/t winter unless there/s a lot of negativity going around. Negativity regarding certain teleconnection indexes...that is.

Take for instance the North Atlantic Oscillation. Conventional wisdom has it the NAO/s gotta be negative. The NAO/s at or above zero? Well then....winter just ain/t happenin' and ain/t gonna happen until it falls below zero.

Same 'thinking' goes for the Arctic Oscillation. AO/s gotta be negative. Can/t get good winter wx without a negative AO.

It/s not that a little negativity is necessarily a bad thing. Positive things can and do come from being negative...but does it have to be that way?

To test the hypothesis that good winter wx requires negative indices of the NAO and AO...30 NEWxSFC snowstorms since December 2002 were reviewed. The results shows there has been plenty of good winter wx when those indices were positive.

The 30 snowstorms used in the analysis are not necessarily representative of all snowstorms in the NE and M-A regions. Forecast contests have not been held for all snowstorms...mainly b/c the progs were not conclusive early enough to warrant a decision to hold a contest or the storm was not expected to produce more than nuisance amount or affect more than a few stations. Some storms in the analysis sample did not produce heavy snowfall.

The North Atlantic Oscillation
The NAO was negative for 16 storms (53%). Seven of those -NAO storms (44%) had a max station snowfall of at least 12". There was one storm where the max station snowfall was at least 20".

Of the 14 storms where the NAO was greater than or equal to zero...five (29%) had max station snowfall amounts of at least one foot. In fact...all five storms had least 20" and three storms had at least 25". Only one storm where max station snowfall was more than one foot had an AO below zero.


There/s a 53% chance that a Contest snowstorm will occur when the NAO is negative. When the NAO is negative...there/s a 23% chance of one station measuring at least one foot of snow and less than 1% chance of a measurement of at least 20".

There/s a 47% chance that a Contest snowstorm will occur when the NAO is positive. When the NAO is positive...there/s a 20% chance of at least one foot and an equal chance of at least 20".

Seems hard not to conclude that -NAO 1) isn/t necessary for Contest snowstorms and 2) isn/t the best for heavy snowfalls in the NE and M-A!

Tomorrow we/ll look at the Arctic Oscillation to evaluate how important it is for this teleconnection index to be negative if you/re looking for a good snowstorm.