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Do Early Cold Winters Typically Reverse Midwinter?

By Joe D'Aleo
Tuesday, November 25, 2008

 

Given the cold late November and early December start, the question most forecasters are wrestling with is whether the late winter will see a reversal to warmth (those that see it are projecting to either late December or late January). We have indicated that warming would be a virtual certainty if a stronger La Nina returned because La Ninas with a westerly QBO (the case this winter) were quite warm in the east and central (most notably 1973/74, 1975/76).

 

Most people recall the winter of 2000/01 where November and December were the coldest ever for the lower 48 states. Midwinter saw some easing but cold and incredible snows returned late winter for parts of the northeast. The also may remember 1989 which had a brutal December but that gave way to a very warm flip in January that lasted the rest of the winter.

 

ONE CASE STUDY

I took a look at New York City which has data back to 1870 and did a November/ December average and listed them in descending order of departure and compared to anomalies in January, February and March. Ironically the majority of cold early winters gave way to cold mid to late winters (65% Januarys were cold, 67% of Februarys and 61% of Marchs were below normal. In 48% of the years, New York January’s were more than 5F below normal. 

 

The results showed some reversals including even the brutal winter of 1976/77 when a frigid December gave way to an even more frigid January but then normal February and warm March.

 

New York City Monthly Anomalies

Yr NovDec

NOVDEC

JAN

FEB

MAR

1880

-8.33

-7.26

-3.93

-3.50

1917

-7.63

-10.26

-2.23

1.90

1872

-7.08

-3.36

-3.13

-4.50

1871

-6.93

-3.16

-2.73

-9.70

1882

-6.03

-6.76

-2.43

-7.50

1876

-5.88

-4.26

4.37

-4.40

1976

-5.13

-9.86

0.87

6.60

1989

-5.13

9.44

7.17

4.90

1910

-4.78

4.34

-1.33

-5.50

1904

-4.58

-2.66

-7.83

0.20

1875

-4.33

4.64

-0.83

-5.80

1873

-4.18

2.24

-1.33

-3.10

1903

-4.08

-6.66

-7.23

-3.80

1890

-4.03

1.84

3.87

-4.40

1926

-4.03

-1.06

3.77

2.80

1955

-3.93

0.04

3.97

-2.80

1886

-3.83

-2.86

-0.63

-7.90

1933

-3.68

2.74

-12.73

-2.90

1962

-3.58

-1.86

-4.33

3.50

1869

-3.43

5.54

-1.33

-6.10

1887

-3.33

-8.96

-3.33

-10.20

1919

-3.23

-8.56

-4.13

-0.30

1901

-3.23

-1.36

-2.93

4.20

1892

-3.13

-8.26

-3.23

-4.70

1883

-3.08

-7.26

1.37

-2.50

1995

-2.93

-1.46

1.27

-1.30

1914

-2.88

2.54

3.27

-3.40

2000

-2.73

1.64

3.27

-0.60

1878

-2.63

-5.06

-4.63

-0.20

1980

-2.38

-5.66

6.67

2.10

1874

-2.33

-8.16

-7.43

-6.10

1921

-2.33

-3.76

0.97

0.80

1958

-2.28

-0.86

-0.53

-0.10

1893

-2.23

1.64

-4.03

2.60

1884

-1.98

-2.56

-9.93

-9.60

1942

-1.88

-1.16

1.97

0.00

1947

-1.83

-6.56

-1.93

1.90

1894

-1.78

-2.16

-8.53

-4.80

1924

-1.73

-3.56

5.27

4.00

1943

-1.73

1.94

0.57

-2.60

1944

-1.73

-6.86

1.27

10.90

1935

-1.63

-2.66

-6.93

5.00

1945

-1.63

2.14

-0.93

9.60

1925

-1.58

0.04

-3.43

-4.50

1922

-1.28

-1.96

-6.43

-3.40

1916

-1.18

0.94

-4.33

-0.90

1870

-1.13

-3.66

-2.43

4.00

1906

-1.08

2.94

-6.73

2.30

1915

-1.03

4.04

-4.73

-7.80

1969

-1.03

-6.86

0.37

-1.50

 

 

 

 

 

 

 

65% BN

67% BN

61% BN

 

 

48%>5F BN

18%>5F BN

20% >5F BN

 

We have discussed that a neutral ENSO or weak La Nin usually have greater intraseasonal variability, mainly due an active MJO which causes the Southern Oscillation Index to bounce around which causes the PNA to flip signs favoring alternating western troughs and eastern troughs.

Hurd “Doc” Willett in a paper (October 1974 Monthly Weather Review) discussing solar cycle variability and seasonal and decadal weather regimes, showed how the 22 year Hale Cycle where successive solar cycles flip magnetic polarity of leading and following spots in pairs, also seemed to influence variability of temperature as well as daily Boston winter temperatures. The current solar minimum should favor lower than normal variability (certainly was the case last winter which was also favored by strong La Nina in bar chart above) and cold Boston winters.

The dashed line represents the maxes and minimums of the maximum (positive) solar cycle. Valid around 2000/01 and 2002/03 and now 2007/08-2008/09. Note these phases had persistent cold while the opposite cycle persistent warmth with a brief cold around the normal January thaw time.

 

THE ANALOG PATTERN THIS YEAR

 

The upper pattern in the most similar years suggest the cold air source will be over Canada much as was the case last year with cold from the Rockies to the northeast. This is the opposite of the CPC forecast, which is always an encouraging factor to us in private industry. They have done some remarkable research in the 1980s and early 1990s but now ignore there own findings  reverting back to relying solely on ENSO and trends and with pressure from above they are always biased warm. If it were not verboten in the old days, a neutral ENSO would lead them to predict a cold winter. Now they use trends ignoring the fact that trends reverse (take for example 2007/08) as factors such as solar and PDO change modes and are forecasting warmth in this neutral ENSO event, although acknowledging low confidence.

 

Here is my expected mean December to March 500mb map. It is on numerous factors, including many of those identified by CPC research. Blue is below normal height and temperatures. It suggests cold in Canada and the northern US and eastern Asia and western Europe, milder in Siberia.  It shows a lot of Atlantic and Davis Straits blocking, evident early so far.

Once again, should La Nina strengthen as the CFS and a few other climate model suggest, the late winter reversal would be more likely as the southeast ridge would rear its ugly head and build west.

 

With the exceptions of three outliers, most of the 21 climate models suggest a neutral (La Nada) or weak La Nina this winter, withy many weakening it late in winter.

 

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