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The Importance Of November Blocking For A La Nina December


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Like we saw last November, the strong November blocking pattern was an early clue to the cold December that the Eastern US experienced.

I put together three groups of composites for the common types of December La Nina patterns. The first composite is made up of cold

Decembers in the East. The second composite is generally mild in the Southeast with an area of colder temperature anomalies centered

back toward the Upper Midwest into the Lakes .The final composite is the one where mild temperatures pretty much run the board. We

usually experience the coldest La Nina Decembers following a strong Greenland Blocking pattern in November. The east based November

blocking pattern usually favors the Upper Midwest and Lakes cold pattern. Less Greenland Bocking in November often precedes a warm December

for many.

Cold December composite East

November

December

Cold December composite Upper Midwest

November

December

Warm December

November

December

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Good stuff bluewave. Basically confirms the idea that the development of a strong west based blocking feature in Nov generally persists through December as well. It would be interesting to look at the Januarys for those years. Offhand, Jan 1956 turned much warmer after a cold Dec, Jan 2009 turned much colder after a mild Dec in the East.

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your analogs by the numbers for NYC...

winter.......Dec....Jan....Feb....Ave....lowest 30 days.......snowfall......big snow...winter minimum...

1950-51...35.0...36.5...36.2...35.9.............33.0...............11.6"............2.9".............9

1955-56...29.7...32.0...36.6...32.7.............27.6...............33.5"..........11.6".............5

1962-63...31.5...30.1...28.3...30.0.............25.9...............16.3"............4.2"............-2

1995-96...32.4...30.5...33.9...32.3.............27.7...............75.6"..........20.2".............5

2000-01...31.1...33.6...35.9...33.5.............30.0...............35.0"..........12.0"...........14

2010-11...32.8...29.7...36.0...32.7.............28.1...............61.9"..........20.0".............6

.................................................................................................................................................................................

1954-55...35.9...31.0...35.0...34.0.............28.6...............11.5"............3.9".............0

1964-65...36.4...29.7...33.9...33.3.............28.0...............24.4"............6.3".............9

1975-76...35.9...27.4...39.9...34.4.............27.1...............17.3"............4.2"............-1

1988-89...35.9...37.4...34.5...35.9.............32.4.................8.1"............5.0".............5

2007-08...37.0...36.5...35.8...36.4.............35.7...............11.9"............6.0"...........10

2008-09...38.1...27.9...36.7...34.2.............27.9...............27.6"............8.3".............6

....................................................................................................................................................................................

1956-57...40.9...28.5...37.3...35.6.............27.8...............21.9"............6.4".............0

1971-72...40.8...35.1...31.4...35.1.............28.6...............22.9"............5.7".............5

1974-75...39.4...37.3...35.8...37.5.............33.0...............13.1"............7.8"...........15

1984-85...43.8...28.8...36.6...36.4.............27.5...............24.1"............5.7"............-2

1998-99...43.2...33.9...38.9...38.7.............31.2...............12.7"............4.5".............9

1999-00...40.0...31.3...37.3...36.2.............26.2...............16.3"............5.5".............3

....................................................................................................................................................................................

1st ave.....32.1...32.1...34.5...32.9.............28.7...............39.0"..........11.8".............6.2

2nd ave....36.5...31.7...36.0...34.7.............30.0...............16.8"............5.6".............4.8

3rd ave.....41.4...32.5...36.2...36.6.............29.1...............18.5"............5.9".............5.0

LT ave......35.6...31.9...32.7...33.4.............??.?................28.3"............?.?".............4.3

The first six analogs had four snowy winters with at least one major blizzard...They averaged close to the long term temperature...The second six analogs had two near average snowfall seasons and four well below average...Temperatures were above the long term but January was below...The third set of six had three winters with slightly below average and three well below average snowfall...Temperatures were well above the long term but January was only slightly...

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To get the brutal cold outcome in the eastern US for Dec. it's the high hieghts in/around AK that will be needed to funnel the cold. The 1 depiction with cold in the east is just such a set-up

Its interesting that all 3 patterns have negative height anomalies over the east coast. So in a Nina, we should really expect troughiness this Nov, but its the strength / location / persistence of the troughs that matters.

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your analogs by the numbers for NYC...

winter.......Dec....Jan....Feb....Ave....lowest 30 days.......snowfall......big snow...winter minimum...

1950-51...35.0...36.5...36.2...35.9.............33.0...............11.6"............2.9".............9

1955-56...29.7...32.0...36.6...32.7.............27.6...............33.5"..........11.6".............5

1962-63...31.5...30.1...28.3...30.0.............25.9...............16.3"............4.2"............-2

1995-96...32.4...30.5...33.9...32.3.............27.7...............75.6"..........20.2".............5

2000-01...31.1...33.6...35.9...33.5.............30.0...............35.0"..........12.0"...........14

2010-11...32.8...29.7...36.0...32.7.............28.1...............61.9"..........20.0".............6

.................................................................................................................................................................................

1954-55...35.9...31.0...35.0...34.0.............28.6...............11.5"............3.9".............0

1964-65...36.4...29.7...33.9...33.3.............28.0...............24.4"............6.3".............9

1975-76...35.9...27.4...39.9...34.4.............27.1...............17.3"............4.2"............-1

1988-89...35.9...37.4...34.5...35.9.............32.4.................8.1"............5.0".............5

2007-08...37.0...36.5...35.8...36.4.............35.7...............11.9"............6.0"...........10

2008-09...38.1...27.9...36.7...34.2.............27.9...............27.6"............8.3".............6

....................................................................................................................................................................................

1956-57...40.9...28.5...37.3...35.6.............27.8...............21.9"............6.4".............0

1971-72...40.8...35.1...31.4...35.1.............28.6...............22.9"............5.7".............5

1974-75...39.4...37.3...35.8...37.5.............33.0...............13.1"............7.8"...........15

1984-85...43.8...28.8...36.6...36.4.............27.5...............24.1"............5.7"............-2

1998-99...43.2...33.9...38.9...38.7.............31.2...............12.7"............4.5".............9

1999-00...40.0...31.3...37.3...36.2.............26.2...............16.3"............5.5".............3

....................................................................................................................................................................................

1st ave.....32.1...32.1...34.5...32.9.............28.7...............39.0"..........11.8".............6.2

2nd ave....36.5...31.7...36.0...34.7.............30.0...............16.8"............5.6".............4.8

3rd ave.....41.4...32.5...36.2...36.6.............29.1...............18.5"............5.9".............5.0

LT ave......35.6...31.9...32.7...33.4.............??.?................28.3"............?.?".............4.3

The first six analogs had four snowy winters with at least one major blizzard...They averaged close to the long term temperature...The second six analogs had two near average snowfall seasons and four well below average...Temperatures were above the long term but January was below...The third set of six had three winters with slightly below average and three well below average snowfall...Temperatures were well above the long term but January was only slightly...

Thanks for putting all the stats together like that. It's interesting that last winter was the snowiest here since 1996. It was also the most negative November NAO since 1995.

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Gibbs, thanks for adding the maps. When I looked at the individual years, there is some overlap between the second and third options so it's

not always that easy determining the extent of the warmth from looking at the November pattern. The colder options were easier to get right.

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  • 4 weeks later...

last years block lasted around two months ending before February...This year might have its strongest blocking in January and February or worse later...Today would have been a snow event along the east coast if it came a month later...The old cold front passage with a trailing low routeen...We may not need record blocking this year to get a good snowfall in the NYC area...But we probably won't get 57" of snow in 31 days like last year...

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  • 3 weeks later...

your analogs by the numbers for NYC...

winter.......Dec....Jan....Feb....Ave....lowest 30 days.......snowfall......big snow...winter minimum...

1950-51...35.0...36.5...36.2...35.9.............33.0...............11.6"............2.9".............9

1955-56...29.7...32.0...36.6...32.7.............27.6...............33.5"..........11.6".............5

1962-63...31.5...30.1...28.3...30.0.............25.9...............16.3"............4.2"............-2

1995-96...32.4...30.5...33.9...32.3.............27.7...............75.6"..........20.2".............5

2000-01...31.1...33.6...35.9...33.5.............30.0...............35.0"..........12.0"...........14

2010-11...32.8...29.7...36.0...32.7.............28.1...............61.9"..........20.0".............6

.................................................................................................................................................................................

1954-55...35.9...31.0...35.0...34.0.............28.6...............11.5"............3.9".............0

1964-65...36.4...29.7...33.9...33.3.............28.0...............24.4"............6.3".............9

1975-76...35.9...27.4...39.9...34.4.............27.1...............17.3"............4.2"............-1

1988-89...35.9...37.4...34.5...35.9.............32.4.................8.1"............5.0".............5

2007-08...37.0...36.5...35.8...36.4.............35.7...............11.9"............6.0"...........10

2008-09...38.1...27.9...36.7...34.2.............27.9...............27.6"............8.3".............6

....................................................................................................................................................................................

1956-57...40.9...28.5...37.3...35.6.............27.8...............21.9"............6.4".............0

1971-72...40.8...35.1...31.4...35.1.............28.6...............22.9"............5.7".............5

1974-75...39.4...37.3...35.8...37.5.............33.0...............13.1"............7.8"...........15

1984-85...43.8...28.8...36.6...36.4.............27.5...............24.1"............5.7"............-2

1998-99...43.2...33.9...38.9...38.7.............31.2...............12.7"............4.5".............9

1999-00...40.0...31.3...37.3...36.2.............26.2...............16.3"............5.5".............3

....................................................................................................................................................................................

1st ave.....32.1...32.1...34.5...32.9.............28.7...............39.0"..........11.8".............6.2

2nd ave....36.5...31.7...36.0...34.7.............30.0...............16.8"............5.6".............4.8

3rd ave.....41.4...32.5...36.2...36.6.............29.1...............18.5"............5.9".............5.0

LT ave......35.6...31.9...32.7...33.4.............??.?................28.3"............?.?".............4.3

The first six analogs had four snowy winters with at least one major blizzard...They averaged close to the long term temperature...The second six analogs had two near average snowfall seasons and four well below average...Temperatures were above the long term but January was below...The third set of six had three winters with slightly below average and three well below average snowfall...Temperatures were well above the long term but January was only slightly...

it looks like the warm December analogs will win out this year...The question is will we get a cold month or will it be mild throughout?...snowfall is a head of these years thanks to the October snowstorm...

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it looks like the warm December analogs will win out this year...The question is will we get a cold month or will it be mild throughout?...snowfall is a head of these years thanks to the October snowstorm...

Uncle, this looked like the third highest AO for November behind 94 and 78.

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/monthly.ao.index.b50.current.ascii.table

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