Winter '12 / '13 - Blocking

Blocking forecast to shift from Bering Sea to Greenland by mid-month!



That...and no evidence of the Gulf of Alaska LOW...heralds winter/s over-due arrival on the east coast.

Winter '12 / '13 - North Atlantic Oscillation - Analog Update

NOV/s NAO index:  -0.58



A 2x2 contingency analysis suggests there/s a 57% probability for the NAO index to average negative during meteorological winter (D-J-F) when NOV/s NAO is negative.

Top analog remains 1998...an el Niño winter.  QBO was fading out and flipped from east to west in JAN.  AO averaged positive.  Not good if it comes to pass given winter/s NAO also averaged positive.

Up one tick are 2008 and 2003...the latter being a good match as AO/s top co-analog along with QBO...and a strong showing by SOI.  ENSO was a warm Nada.  DC measured a paltry 13" and RIC 6".  The good snows that winter were in mainly in south coastal NE and the northern M-A [PVD (119%)...BDR (189%)...BGM (137%)...NYC (155%)...ABE (124%)...EWR (177%)...and RDU (199% from a late season low-latitude thump)].

Season-total snowfall at NEWxSFC Contest stations during Winter '03 / '04 totaled 999"...8" above period-of-record normal (PoRN).

None of the analog years look particularly promising  b/c almost all go positive in JAN and FEB.  Negative NAO falls into the nice-to-have category but it's not all that important for it to be in such a constant state.

Winter '12 / '13 - Arctic Oscillation - Analogs

Analog years selected based on the smallest sum of square errors between current year/s monthly AO index and historical values since 1950.

Strongest analog year remains 2003 with the NOV update.
The same year is the top ranked analog for SOI...QBO...and NAO.

The 2x2 contingency table analysis suggests a 76% probability for meteorological winter/s AO to be negative.

Season-total snowfall at NEWxSFC Contest stations during Winter '03 / '04 totaled 999"...8" above period-of-record normal (PoRN).

AO during winter '03 / '04 averaged -0.983.  DEC/s AO of 0.265 was followed by -1.686 in JAN and -1.258 in FEB.

Winter '12 / '13 - Waiting in the Wings

Latest Week2 ensemble forecast from NOAA/s Physical Science Division's Global Forecast System (GFS 1998) shows a decided change in the long wave pattern over the NHEMI.

RED (BLUE) areas are positive (negative) anomalies.

The current high zonal index to an occasional Trof-W / Ridge-E flow regime flips to Ridge-W / Trof-E with a hi-latitude block setting up over Greenland and the establishment a strong PNA ridge.

The sub-tropical jet turns its attention away from the PAC NW gets busy delivering tropical moisture across the southern tier and Gulf of Mexico.

Low-level cold air is indicated east of the Rockies courtesy the strong PNA ridge along 125°W (preferred position for EC snow storms) and the Greenland block.

Winter '12 / '13 - Arctic Oscillation - Meteorological Winter - Day One

Not sure it means anything but here's the state of the AO during its 63-year period of record on the first day of meteorological winter.



BLUE line is the observed AO index on 01-DEC.
RED line is the 9-point binomial filter.  The filter removes noise from the signal to highlight the trend.

The DEC-12 AO is the third lowest on record behind DEC-85 (-3.783) and DEC-97 (-2.603).



Same idea for AO/s sister...the North Atlantic Oscillation (NAO).

Winter '12 / '13 - Season-total Forecast Contest - Forecast Summary

Eleven forecasters this year.
Good to see ya'll back again.

Forecaster's are bullish about an above average season.



YELLOW cell indicates the winner of last year/s season-total forecast contest.
BLUE cells are the 25th percentile.
RED cells are the 75% percentile.
PORN is the Period of Record Normal.



Everyone's complete forecast is available on the Contest/s web site.

Winter '12/ '13 - Arctic Oscillation - Is November A Leading Indicator?

UPDATE (14-DEC-14)
Winter '12 / '13 AO:  -1.222

UPDATE (04-DEC-12)
NOV/s AO:   -0.111.
Probability the average AO is negative for meteorological winter '12 / '13:  76%

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Little doubt NOV/s index will come in negative despite an early 15-day run of above zero values.

A 2x2 contingency table of NOV/s AO index and winter/s average (D-J-F) index suggests there/s a strong association between the two when NOV/s AO is < 0.



When NOV/s AO is < 0...there/s a 76% chance the winter/s average AO will also be negative.  The table's precision is 63%...where precision is the proportion of negative cases predicted correctly [a / (a + c)].

Winter '12 / '13 - Outlooks

Thread updated periodically as new outlooks and forecasts are issued from a variety of sources.

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Dr. Todd Crawford - WSI Chief Meteorologist...

While this El Nino event now appears to be a dud, most of our more skillful climate indicators suggest...very cold air will be in plentiful supply across western and central Canada this winter, with frequent border crossings into the northern US.

Currently, we do not expect the kind of frequent atmospheric blocking in the North Atlantic (otherwise known as the negative NAO) that would result in more extreme and more widespread cold in the eastern US.  However, trends in some of the long-lead indicators suggest...this assumption may be challenged, and...the risk to the forecast in the eastern US is towards (sic) the colder side.

In the NE US...
DEC - colder than normal, except northern New England
JAN - colder than normal
FEB - warmer than normal

More...

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Harvey Leonard, Chief Meteorologist, WCVB-TV (Boston...MA):

...expect a somewhat colder than average winter, with at least average snowfall, and possibly somewhat above average snowfall.

More...

Read more »

Winter '12 / '13 - North Atlantic Oscillation - Trends

Chart 1 - meteorological winter/s average NAO and 9-point binomial filter.
Binomial filter removes noise from signal to reveal trends.

1950s through 1970s...predominantly negative
1980 ...period of transition toward positive
1990s through 2000s...predominantly positive...trending toward negative in the 2010s.



Chart 2 - tally of all monthly NAO sign by calender year.

Noisy signal during most decades; however...positive index began to prevail during the late 1990s.

Value of '6' are years where positive and negative months during the calender year were equal.



Chart 3 (above) - tally of the monthly NAO sign by half-decade.

Slight advantage for negative index during the 1960s through mid-1970s...alternating during late 1970s through the 1980s...strong positive index prevailed during the late 1980s through the early 2000s...and negative ever since.

Value of '30' are periods where positive and negative months were equal.

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Chart 4 - tally of the monthly NAO sign by decade.

Positive decadal index between the 1970s until 2000s after which negative has been the trend.
Value of '60' are periods where positive and negative months were equal.



The 5-year moving average during meteorological winter turned negative in 2009 has been negative ever since.  The last time the 5-year moving average was negative occurred between 1977 - 1981 and 1954 - 1972.

Trending:  negative NAO.

Winter '12 / '13 - North Atlantic Oscillation - November As Oracle

As it turns out...there/s a strong association between the sign of November/s monthly NAO index and the sign of the average NAO index during meteorological winter (D-J-F).  It's strongest when NOV/s NAO index is positive.

A chi-square test on NOV/s monthly values and average value of winter/s NAO suggests the sign of NOV/s NAO has a measure of predictive skill.

The 2x2 contingency counts the number of events when the the sign of winter/s NAO matched the sign of NAO in NOV.

The distribution of events offers these probabilities:
70%  + NOV ==> + Winter
30%  + NOV ==> - Winer

43% - NOV ==> + Winter
57% - NOV ==> - Winter

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If the signs of NOV/s NAO and winter/s NAO events were independent / unrelated...then the distribution of events would follow a normal 'bell' curve where...

Positive NOV and positive (negative) winter:  15 (12) events
Negative NOV and positive winter (negative):  19 (16) events

The 2x2 contingency analysis reveals the sign of winter/s NAO is not independent (3.1% chance of Type I error) from the sign of NOV/s NAO.

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As a footnote...OCT/s NAO has no 'predictive' value b/c it is independent from the sign of winter's NAO.

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CPC/s monthly NAO index here.