Going Negative - Part IV

Snowfall amounts for 30 Contest snowstorms since December 2002 were stratified by quartiles to determine whether they were heavy, light, or somewhere in between. The analysis seeks to determine whether negative teleconnection indices are favorable for the best winter wx...defined as producing heavier snowfall events.

Heavy snowfall is defined as belonging to at least the 75 percentile (>= 16") of the 30 Contest storm dataset. Light snowfall is defined as belonging to no more than the 25 percentile (<= 5.6"). The analysis did not control for SN:H2O, areal distributions, events where liquid or freezing precipitation reduced snfl, or the number of stations affected.

NAO
5 of the 8 (62%) max station snfl amts occurred when the NAO was greater than 0.
3 of the 9 (33%) min station snfl amts occurred when the NAO was greater than 0.

Heavier snfl is more likely when NAO greater than 0.

3 of the 8 (38%) max station snfl amts occurred when the NAO was less than 0.
6 of the 9 (67%) min station snfl amts occurred when the NAO was less than 0.

Lighter snfl is more likely when NAO less than 0.

AO
5 of the 8 (62%) max station snfl amts occurred when the AO was greater than 0.
4 of the 9 (44%) min station snfl amts occurred when the AO was greater than 0.

Heavier snfl is more likely AO greater than 0.

3 of the 8 (37%) max station snfl amts occurred when the AO was less than0.
4 of the 9 (44%) min station snfl amts occurred when the AO was less than 0.

Lighter snfl is more likely when AO less than 0.

PNA
5 of the 8 max (62%) station snfl amts occurred when the PNA was greater than 0.
5 of the 9 min (56%) station snfl amts occurred when the PNA was greater than 0.

Heavier snfl is more likely when PNA > 0.

3 of the 8 max (38%) station snowfall amounts occurred when the PNA was less than 0.
3 of the 9 min (33%) station snfl amts occurred when the PNA was less than 0.

Heavier snfl is slightly more likely when PNA less than 0.

What/s It All Mean?
The limited dataset suggests PNA plays a bigger role in the heavier snowfall events. +PNA suggests an amplified 'ridge-W / trof-E' UA flow regime that delivers cold air from the NW NOAM and...as described by the loading pattern and Sutcliff/s 'self-development' theory...is favorable for cyclogenesis along low latitudes of the EC.

Negative values for the AO and NAO suggest an UA flow regime conducive to colder than normal temperatures in the NE but negative values of these teleconnection indices are not necessarily pre-conditions for heavier snfl. In fact...negative values may work against heavier snfl events b/c cold air is dry air and unless the mid-level flow is amplified...then cyclogenesis is unlikely to occur.

The various teleconnection indices are useful tools to diagnose aspects of atmosphere/s configuration but should not be seen a prerequisites for strong to severe winter wx. Good snows have even occurred even when PNA is negative...as have good snows when the AO and NAO are positive.