Going Negative - How Much for Dulles?

For lesser daily snowfalls and snowfalls of 12" or more...there/s a higher chance of occurrence with +PNA...+NAO...and -AO. -NAO is preferred for 7 - < 12" amounts.



With +PNA...+NAO is more likely for daily snowfall below 7".



With +NAO...-AO is more likely for lesser daily snowfalls and daily snowfalls of 12" or more.

Dulles is a short distance WNW of DCA…yet IAD/s snowfall climatology is 35% greater than DCA. Each station/s micro-climate and elevation may be why more snow is observed at IAD (307” MSL) than DCA (59’ MSL).

Neither location will ever be considered a snow capital but there are interesting differences between them for the preferred sign of NAO.

For the Big 3…
For daily snowfalls up to 5” and +12” amounts…
IAD prefers +PNA…+NAO…-AO
DCA prefers +PNA…-NAO…-AO

For 5 < 7”…
IAD: +PNA…+NAO…+AO
DCA: +PNA…+NAO…-AO

For 7 - < 12”…
IAD: +PNA…-NAO…-AO
DCA: +PNA…+NAO…-AO

+PNA and -AO are common contributing factors @ both stations except for 5 - < 7” amounts. The sign of NAO flip flops taking the opposite sign between daily snowfall categories and stations.

The more stations examined...the -NAO CW b/comes more and more questionable.