Winter '12 / '13 - North Atlantic Oscillation: Analogs

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

It's notable how every analog becomes positive to ever-so-slightly negative during the coming winter. 

ENSO (MEI):
1998 - moderate la Nina.
1993 - warm la Nada after a moderate el Nino
2008 - weak la Nina
2003 - warm la Nada
2004 - weak el Nino

Best match:  2003

PDO:
1998 - weak negative
1993 - moderate positive
2008 - moderate negative
2003 - weak positive
2004 - weak positive

Best match:  2008

QBO:
1998 - weakening easterlies, flip to westerlies in JAN
1993 - strengthening easterlies
2008 - mid-cycle westerlies
2003 - weakening easterlies, flip to westerlies in FEB
2004 - weakening westerlies, flip to easterlies in JAN

Best match:  1998; 2003

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

Next up:  period-of-record trend analysis and the correlation between the northern annular oscillation phase (NAO and the Arctic Oscillation) and sunspots.  Spoiler alert:  not lookin'good.

Winter '12 / '13 - North Atlantic Oscillation: Long-range Signals and Long-term Trends

Up until a few years ago...the UKMET office issued a long-lead forecast of the North Atlantic Oscillation's (NAO) phase for the upcoming winter.  The forecast was based on the correlation between May's sea-surface temperature anomalies (SSTA) in the western Atlantic ocean and the phase of the NAO.  Geo-potential height anomalies at 500 mb in the same general region were also found to have predictive value.

They claimed these correlations had predictive value ~67% of the time...a far cry better than the brain-dean CW about how seasonal NAO forecasting is unpossible.

If May's SSTA matches the pattern in the western Atlantic ocean...then a +NAO is expected to be the dominant state during the upcoming winter.  Above normal SST in the offshore waters of the NE coast...cold water SE of Iceland and warm anomalies to the northeast point toward a +NAO.  If the pattern is reversed...then a -NAO is forecast.

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This year...May's SSTA were a good match to the anomaly pattern shown above off the NE coast (1) but not so much elsewhere (2,3).

Area 1...the offshore waters of the NE...+SSTAs ==> +NAO

Area 2...SW of Iceland...+SSTAs ==> -NAO

Area 3...NE of Iceland...-SST anomalies ==> -NAO

SSTAs offer a decidedly mixed signal.

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At 500 mb anomalies for MAY-12...

Positive height anomalies over Greenland ==> -NAO
Positive height anomalies over western Europe ==> +NAO
The effect of a negative action center INVOF the Azores is unknown.
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This winter's NAO signal based on the UKMET/s long-lead conceptual model is unambiguously ambiguous.

Sea-surface temperature anomalies off the NE coast suggest +NAO while SSTAs off the coast of Greenland suggest -NAO.  Height anomalies at 500 mb over Greenland signal -NAO and a + NAO over western Europe.  The effect of the Azores' strong negative signal is unknown.

Next up:  Analogs

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Earlier posts about the UKMET NAO forecast here.

Winter '12 / '13 - Eurasia Snow Cover - October

Period of record median:  9,599,610 km²
October-12:  11,106,205 km²

October-12 Eurasia snow cover...as reported by Rutgers Snow Lab...is 16% above normal.  This bodes well for a cold and snowy winter in the eastern US...according to the statistically significant correlation between these global two features discovered by AER's Dr. Judah Cohen.

...Eurasian snow cover during this year’s October has increased far more rapidly than...is normally the case (the corresponding index value exceeds two-standard deviations).

Given the large anomaly for the predictor variable, the following winter will be a good test for assessing if the approach is suitable for real-time seasonal forecasts.¹

Eurasia OCT snow cover : season-total snowfall (D-J-F-M) at NE and MA Contest stations in recent winters...
'09 / '10:  11,288,371 km² - 1,225" (observed*) v. 908" (normal*)
'10 / '11:  10,615,933 km² - 1,426" (observed) v. 921" (normal)
'11 / '12:  9,293,740 km² - 393" (observed) v. 934" (normal)

* SBY removed for lack of station snowfall data.



Blue dotted - observed snow cover
Red - 9-point binomial filter
Orange - period of record median snow cover
Yellow dashed - one standard deviation

The 9-point binomial fiter shows the long-term trend by removing noise from the signal.



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Reading room...
- A new index for more accurate winter predictions (pdf)
GEOPHYSICAL RESEARCH LETTERS, VOL. 38, L21701

- Eurasian Snow Cover Variability and Links with Stratosphere-Troposphere

Coupling and Their Potential Use in Seasonal to Decadal Climate Predictions (pdf)

Climate Test Bed Joint Seminar Series

NCEP, Camp Springs, Maryland, 22 June 2011

Winter '11 / '12 - FINAL Standings

After a measley two contest-worthy snow storms...the 13th annual NEWxSFC season for the Winter of '11 / '12 comes to a close.

Congratulations to donsutherland1 for successfully defending his title as Chief forecaster!

Under the 'two-thirds' rule...the best 'two out of three' Z-scores are used to compute the final standings. There were only two events this winter...so only forecasters who entered forecasts for both storms qualified for ranking in the FINAL standings.  Data used to compute the standings are posted at the Contest web site here.

Z-scores are used to standardize / normalize forecast errors for each snow storm so at the end of the season...the 'equalized' scores can be averaged.

An expanded data table with higher resolution graphics and additional measures of forecaster skill available at the Contest's home page.

Looking forward to seeing y'all again next winter!

Winter '11 / '12 - Season-total Forecast Contest - FINAL Results

Roger Smith FTW!
Roger won last year...as well.
Congratulations!

donsutherland1 placed a close 2nd.

Herb @ MAWS takes 3rd.

Honorable Mention goes to Donald Rosenfeld.

PORN is the 'period of record normal' or climatology.

Skillful forecasts are those that beat PORN climatology.

A forecaster's batting average represents how many of their stations had the lowest absolute forecast error.

Everyone's forecast has been verified and posted to the Contest/s web site here.

Hope to see y'all back again next winter.

Winter '11 / '12 - Season-total Snowfall Forecast Contest - Station Summary

Forecast station summary ...



Green shading ==> best 1/3 in category.
Red shading ==> worst 1/3 in category.

SBY carries 2". (UPDATED 04-SEP-12:  VantagePoint reports season-total of 4.2".  No change in standings.)  Maybe there was more.  Hard to know since AKQ no longer reports snowfall data for this station.

Pitiful excuse for a winter this season.

Snowfall totals barely got off the mat at most locations.

Anomalously strong polar vortex persisted well into meteorological winter's second month despite -QBO...further evidenced by the +AO.  NAO remained positive D-J-F save for a few brief excursions below zero.

Up next...forecaster summary and FINAL standings.

Winter '11 / '12 - Meteorological Winter - Month Three

CAR alone enjoyed a 'normal' snowfall this winter.  No other station came even close to normal.

March is the last month for the 'season-total' snowfall forecast contest.  Latest round of long range progs hold little hope for a late rally.

Climo columns are the summed monthly totals for DEC...JAN...and FEB.

Teleconnections for FEB (top) and meteorological winter (bottom).

Winter '11 / '12 - Snow Storm #2 - Final Results

Springfield MA

1st Place - donsutherland1
SUMSQ: 76.05
SUMSQ Z: -1.079
STP: 6.35 (4)
TAE: 20.75 (1)
AAE: 1.60 (1)

2nd Place - Brad Yehl
SUMSQ: 109.66
SUMSQ Z: -0.651
STP: 18.90 (9)
TAE: 26.50 (2)
AAE: 2.04 (5)

3rd Place - TQ
SUMSQ: 117.34
SUMSQ Z: -0.553
STP: 8.05 (6)
TAE: 30.95 (4)
AAE: 2.06 (6)

Honorable mention - ilibov
SUMSQ: 125.21
SUMSQ Z: -0.453
STP: 9.20 (7)
TAE: 33.00 (7)
AAE: 1.74 (2)
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SUMSQ: sum of square errors
STP: storm-total precipitation error
TAE: total absolute error
AAE: average absolute error
(number): category rank

Verified forecasts and storm summary at the Contest/s web site.

Winter '11 / '12 - Snow Storm #2 - Preliminary Verification

Preliminary storm-total snowfalls for Wednesday and Thursday from CDUS41...CXUS51...and PNS...as of 4 PM Friday.

Based on PNSBOX and NOHRSC...no evidence for any accumulation at HYA.  ORH value came from PNSBOX b/c no report was available from climate bulletins.   ORH STP may be revised if new data become available.

Several stations in the data table do not have SN:H2O reported b/c their liquid totals included mixed precipitation.

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Four new daily records.
WED...29-FEB-12
BDL - 4.4" (4.4"; 2008)
ALB - 4" (0.8"; 2008)
ORH - 4" (3.1"; 1968)

THU...01-MAR-12
PWM - 13" (9.3"; 2005)

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Please report any errors and drop a link to the correct data in Comments.

Final results and storm summary Saturday evening.

Winter '11 / '12 - Snow Storm #2 - The Forecasts

Posted at the Contest/s web page here.