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How important is the NAO for NYC snowfall during La Nina?


ORH_wxman
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I had some older research on the NAO and different cities that I stumbled across recently while organizing my files, and I decided to see update the NYC graph for La Nina. For the NAO, I used the classical SLP Hurrell method as it has a bit of a wider range than the CPC upper air method. But the two methods almost always agree on the sign of the NAO.

NYC_snowfall_LaNina.thumb.jpg.ffe24aaf0beaea5d3695b6d3e66cda90.jpg

 

 

You can see from the graph that about 41% of the variance in snowfall during La Nina can be explained by the NAO. That's a pretty solid relationship, but it obviously still leaves a lot of wiggle room. A few things stand out though:

1. The chances of a big winter are heavily skewed toward a -NAO. In fact, zero La Ninas produced solidly above average snowfall at KNYC without help of a -NAO.

2. The cluster of snowfalls "near climo average" (basically between about 22-31 inches) has almost no relationship to the state of the NAO.

3. The truly terrible snowfall winters are heavily skewed toward a +NAO. Only 1 out of the 7 winters with less than 15" at KNYC had a negative NAO and both winters with under 10" had a positive NAO.

 

In short, it seems you can use the state of the NAO to rule out one outcome at NYC but not the other two. For example, if we have a -NAO, we can very likely rule out a really terrible winter but we cannot rule out a near climo or above average snowfall winter. Of course, the sample size isn't enormous here, so you actually truly cannot rule anything out. The 1954-1955 outlier does show the danger of that. But the relationship is certainly strong with those very good years and very bad years.

 

 

 

 

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1 hour ago, ORH_wxman said:

I had some older research on the NAO and different cities that I stumbled across recently while organizing my files, and I decided to see update the NYC graph for La Nina. For the NAO, I used the classical SLP Hurrell method as it has a bit of a wider range than the CPC upper air method. But the two methods almost always agree on the sign of the NAO.

NYC_snowfall_LaNina.thumb.jpg.ffe24aaf0beaea5d3695b6d3e66cda90.jpg

 

 

You can see from the graph that about 41% of the variance in snowfall during La Nina can be explained by the NAO. That's a pretty solid relationship, but it obviously still leaves a lot of wiggle room. A few things stand out though:

1. The chances of a big winter are heavily skewed toward a -NAO. In fact, zero La Ninas produced solidly above average snowfall at KNYC without help of a -NAO.

2. The cluster of snowfalls "near climo average" (basically between about 22-31 inches) has almost no relationship to the state of the NAO.

3. The truly terrible snowfall winters are heavily skewed toward a +NAO. Only 1 out of the 7 winters with less than 15" at KNYC had a negative NAO and both winters with under 10" had a positive NAO.

 

In short, it seems you can use the state of the NAO to rule out one outcome at NYC but not the other two. For example, if we have a -NAO, we can very likely rule out a really terrible winter but we cannot rule out a near climo or above average snowfall winter. Of course, the sample size isn't enormous here, so you actually truly cannot rule anything out. The 1954-1955 outlier does show the danger of that. But the relationship is certainly strong with those very good years and very bad years.

 

 

 

 

Excellent post!  Thanks so much for leaving it here.

WRT 1954-55, what did temps look like in DJFM?  Did a craptastic Pacific doom us?

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16 minutes ago, Eduardo said:

Excellent post!  Thanks so much for leaving it here.

WRT 1954-55, what did temps look like in DJFM?  Did a craptastic Pacific doom us?

Temps were actually near normal (even slightly below)...but the Pacific definitely wasn't very favorable for east coast storms. There was probably an element of bad luck in there as well for the total to be as low as it was in that pattern. You normally would have expected at least a few moderate events out of that look.

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Good stuff.

Being on the southern edge of the huge seasonal snowfall gradient that exists in the lower half of the northeast, it usually takes a -NAO to get a solid winter around here, but +NAO winters aren't quite the same death sentences they are once you get to Philly and further south, either.

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33 minutes ago, masomenos said:

Good stuff.

Being on the southern edge of the huge seasonal snowfall gradient that exists in the lower half of the northeast, it usually takes a -NAO to get a solid winter around here, but +NAO winters aren't quite the same death sentences they are once you get to Philly and further south, either.

ENSO starts becoming a much bigger factor further south too. BWI actually only has a 0.20 R squared for the NAO during La Nina...its mostly just because La Nina is pretty bad there regardless of what the NAO does. La Nina signal overwhelms the NAO that far south.

 

On the flip side, the interior around NYC (esp to the north) can still do well without a -NAO in La Nina, though it is still not easy. Same deal in New England, there's more instances of decent winters in a +NAO La Nina, but the really good ones are still overwhelmingly in favor of a -NAO and the huge ratters almost all have a +NAO.

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5 hours ago, uncle W said:

the near la nina winters of 1962-63, 1967-68 had below average temperatures and snowfall...1961-62 ( a mei la nina winter) was colder than average with less snow than average...the nao was negative on average all three winters especially 1962-63...

Baroclinic zone was likely south of us; NAO values were arguably too negative in much of those winters.

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Oct-Nov-Dec during la nina and weak negative years...monthly ave temp...total snow up till 12/31...ave monthly ao/nao values...

red monthly temp= above average...red snowfall= below average...red ao/nao= positive...

blue monthly temp= below average...blue snowfall= above average...blue ao/nao = negative...

black monthly temp= near average...black snowfall=near average...black ao/nao= near neutral...

...monthly temperature/snowfall.......monthly AO value...............monthly NAO value.......

year......Oct....Nov....Dec...snow........Oct.......Nov.......Dec ao.....Oct.....Nov.....Dec...nao

1950....60.0...48.4...35.0.....3.8".....-0.379...-0.515...-1.928.......0.85...-1.26...-1.02...below average snowfall season...

1954....61.7...46.4...35.9.....0.1"......0.513...-0.328....0.553.......0.60.....0.40....0.69...below average snowfall season...

1955....59.8...44.3...29.7.....4.3"......1.099...-1.342...-0.444......-1.47....-1.29....0.17...above average snowfall season...

1956....58.1...46.7...40.9.....0.9"......1.139...-0.066....0.001.......0.88.....0.51....0.10...near average snowfall season...

1961....61.1...48.8...35.5.....7.7"......0.203...-0.010...-1.668.......0.51....-0.62...-1.48...6.2" storm 12/23-24...below average snowfall season...

1962....57.4...43.2...31.5.....4.5".....-0.016...-1.112...-0.711.......0.41....-0.23...-1.32...below average snowfall season...

1964....55.0...49.4...36.4.....3.1"......0.342...-0.344...-0.246.......0.74....-0.01...-0.15...near average snowfall season...

1966....56.2...48.9...35.7.....9.1".....-1.077....0.111...-1.401......-0.68....-0.04....0.72...7.1" storm 12/24...above average snowfall season...

1967....57.2...42.5...38.2.....8.7"......1.299....0.334...-0.347.......0.07.....0.60...-0.45...below average snowfall season...

1970....58.9...48.5...34.4.....2.4"......0.098....0.378...-0.399......-0.92....-0.60...-1.20...below average snowfall season...

1971....62.7...45.1...40.8.......T.......1.185.....0.419....0.824........0.58....-0.20....0.60...near average snowfall season...

1973....60.2...48.3...39.0.....2.8"......0.337....0.002...-0.181.......-1.24....-0.93....0.32...near average snowfall season...

1974....54.1...48.2...39.4.....0.2".....-1.024...-0.435....0.556.......0.49....-0.54....1.50...below average snowfall season...

1975....59.2...52.3...35.9.....2.3"......0.138....0.619....1.290......-0.54.....0.41....0.00...below average snowfall season...

1983....57.9...48.9...35.2.....1.6"......1.369...-0.688....0.186.......0.65....-0.98....0.29...near average snowfall season...

1984....61.8...47.3...43.8.....5.5".....-0.270...-0.966....0.446......-0.07....-0.06....0.00...near average snowfall season...

1985....59.5...50.0...34.2.....0.9"......1.035...-1.218...-1.948.......0.90....-0.67....0.22...below average snowfall season...

1988....52.8...49.4...35.9.....0.3"......0.032...-0.035....1.679......-1.08....-0.34....0.61...below average snowfall season...

1995....61.6...43.6...32.4...14.4"......0.075...-0.723...-2.127.......0.19....-1.38...-1.67...7.7" storm 12/19-20...above average snowfall season...

1998....57.6...48.1...43.2.....2.0"......0.294...-1.449....1.353......-0.29....-0.28....0.87...below average snowfall season...

1999....56.0...50.6...40.0.......T.......-0.006....0.611....1.043.......0.20.....0.65....1.61...below average snowfall season...

2000....57.0...45.3...31.1...13.4"......0.317....-1.581...-2.354.......0.92....-0.92...-0.58...12.0" storm 12/30...above average snowfall season...

2005....57.9...49.6...35.3.....9.7"......0.030.....0.228...-2.104......-0.98....-0.31...-0.44...above average snowfall season...

2007....63.6...45.4...37.0.....2.9"......0.383....-0.519....0.821.......0.45.....0.58....0.34...below average snowfall season...

2008....55.1...45.8...38.1.....6.0"......1.676.....0.092....0.648......-0.04....-0.32...-0.28... average snowfall season...

2010....58.1...47.9...32.8...20.1".....-0.467....-0.376...-2.631.....-0.93....-1.62...-1.85...20.0" storm 12/26-27...above average snowfall season...

2011....57.1...51.9...43.3.....2.9"......0.800.....1.459....2.221.......0.39.....1.36....2.52..below average snowfall season

2012....58.0...43.9...41.5.....5.1".....-1.514....-0.111...-1.749.....-2.06....-0.58....0.17...near average snowfall season...

2013....60.2...45.3...38.5.....8.6"......0.263.....2.029....1.475......-1.28.....0.90....0.95...above average snowfall season...

2016....58.8...49.8...38.3.....3.2".....-1.917....-0.611....1.786.......0.41....-0.16....0.48...average snowfall season...

only 1962, 2000 and 2010 had no months in the red for temps...1973 and 2016 had all three months with temps in the red...

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November was the giveaway  that the 95-96, 00-01, and 10-11 La Nina winters would be so big for NYC. Those three winters featured strong November -NAO/-AO patterns which carried over into the winter. The EPO was also negative for all three Novembers. A lack of major November warmth in NYC defined  those 3 Novembers which averaged +0.8, -2.3, and -4.0.

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the years with a negative ao or nao in December...the Dec nao epo pdo qbo for comparisons...

...after looking at Dec. 1950 you would think it was a good month for snow and cold...when the AO hit its lowest point of the winter on 12/26/50 NYC got 3" of snow and lows in the single digits that day...1961 another year with warmth in Oct/Nov did have a 6-10" snowstorm for Christmas...1962 was a lot colder and did have above average snow south of the city...Philadelphia did well...there was light snow on Christmas day...1966 had a negative ao in December but the nao was positive on average...it did have a 7" snowstorm for Christmas...1970 had a cold last ten days of the month with a little snow and ice just before Christmas...there was a 6-7" snowstorm on New Years day 1971...1985 had a very negative ao and was a cold December...the nao was positive on average and snowfall was light...there was a 4" storm just south of the city before Christmas...Bricktown N.J. had snow on the ground Christmas morning...there was snow in the air Christmas day but it didn't stick...1995 had a 7-8" snow on the 19-20th...snow on the ground Christmas morning with flurries Christmas evening...1995 was a very cold December...2000 was a cold December with light snow a few days before Christmas...big snowstorm on the 30th...2005 started out cold and snowy with a 6" storm on the 8th...the coldest temperature of the winter came mid month...it did get milder the second half with a little snow the end of the month...2010 was very cold with a big snowstorm just after Christmas...2012 was a mild December...the nao was positive that month...snowfall was verylight but the was some snow flakes around Christmas but it didn't stick in the city...

December/year...AO.......NAO.....EPO.....PDO.....QBO...red=positive...blue=negative...

1950...............-1.928....-1.02....-0.39....-0.76....-03.31

1961...............-1.668....-1.48....-1.92....-2.69.....06.25

1962...............-0.711....-1.32....-0.50....-0.96....-15.16

1966...............-1.401.....0.72.....0.74....-0.32.....13.26

1970...............-0.399....-1.20....-0.05....-0.97....-17.39

1985...............-1.948.....0.22.....1.25......0.38.....09.51

1995...............-2.127....-1.67.....1.07.....0.16....-04.57

2000...............-2.354....-0.58.....0.20.....0.52....-14.56

2005...............-2.104....-0.44.....0.35.....0.20....-25.40

2010...............-2.631....-1.21.....0.27....-1.21.....10.97

2012...............-1.749.....0.17.....0.12....-0.59....-10.02

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the years with a negative ao or nao in December...the Dec nao epo pdo qbo for comparisons...

...after looking at Dec. 1950 you would think it was a good month for snow and cold...when the AO hit its lowest point of the winter on 12/26/50 NYC got 3" of snow and lows in the single digits that day...1961 another year with warmth in Oct/Nov did have a 6-10" snowstorm for Christmas...1962 was a lot colder and did have above average snow south of the city...Philadelphia did well...there was light snow on Christmas day...1966 had a negative ao in December but the nao was positive on average...it did have a 7" snowstorm for Christmas...1970 had a cold last ten days of the month with a little snow and ice just before Christmas...there was a 6-7" snowstorm on New Years day 1971...1985 had a very negative ao and was a cold December...the nao was positive on average and snowfall was light...there was a 4" storm just south of the city before Christmas...Bricktown N.J. had snow on the ground Christmas morning...there was snow in the air Christmas day but it didn't stick...1995 had a 7-8" snow on the 19-20th...snow on the ground Christmas morning with flurries Christmas evening...1995 was a very cold December...2000 was a cold December with light snow a few days before Christmas...big snowstorm on the 30th...2005 started out cold and snowy with a 6" storm on the 8th...the coldest temperature of the winter came mid month...it did get milder the second half with a little snow the end of the month...2010 was very cold with a big snowstorm just after Christmas...2012 was a mild December...the nao was positive that month...snowfall was verylight but the was some snow flakes around Christmas but it didn't stick in the city...

December/year...AO.......NAO.....EPO.....PDO.....QBO...red=positive...blue=negative...

1950...............-1.928....-1.02....-0.39....-0.76....-03.31

1961...............-1.668....-1.48....-1.92....-2.69.....06.25

1962...............-0.711....-1.32....-0.50....-0.96....-15.16

1966...............-1.401.....0.72.....0.74....-0.32.....13.26

1970...............-0.399....-1.20....-0.05....-0.97....-17.39

1985...............-1.948.....0.22.....1.25......0.38.....09.51

1995...............-2.127....-1.67.....1.07.....0.16....-04.57

2000...............-2.354....-0.58.....0.20.....0.52....-14.56

2005...............-2.104....-0.44.....0.35.....0.20....-25.40

2010...............-2.631....-1.21.....0.27....-1.21.....10.97

2012...............-1.749.....0.17.....0.12....-0.59....-10.02

Bump...anyone?
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