Winter '17 / '18 - La Nina Teleconnections and Flavors

Image courtesy The International Research Institute for Climate and Society (IRI)

The Flaw of Averages ... not all La Ninas are created equal.

 

 

 Images courtesy NOAA Climate.gov - ENSO Blog

Winter '16 / '17 - Arctic Oscillation (AO) Analog Verification

The analog forecasting technique seeks similarities to the AO state during the multi-month run-up to the coming winter with same AO run-ups of winters past.

The NEWxSFC method ranks analog years by their the sum of square errors (SSE) statistic.
Lower SSE errors ==> stronger analog

Arctic Oscillation (AO) Index Analog Forecast Verification

In the run-up to Winter '16 / '17 ... the leading analog was '12 / '13 followed by '73 / '74 ... '02 / '03 ... '74 / '75 ... and '88 / '89.  A qualitative assessment of the forecast's accuracy would rate the top three analogs as 'poor' ... IOW ... useless.

Winter '12 / '13 NAO oscillated weak negative to strong negative; whereas ... Winter '16 / '17 was essentially a mirror opposite.  The closest analogs ... on the basis of the AO remaining positive throughout the three-month forecast period ... were ranked last ('88 / '89) and next to last ('75 / '76).

Conclusion:  The top three Winter '16 / '17 AO analogs showed little ... if any ... skill.

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An alternative forecasting technique looks at the AO's sign for any calendar-year's month preceding the pending winter as a potential leading indicator of the AO's sign for D-J-F period.

Results from a chi-square 'test for independence' infers a statistically significant relationship ... at the 95% confidence level and a p-value < 0.05 ... between NOV's AO sign and AO's sign of the upcoming D-J-F period.  IOW ... if NOV's AO is negative (positive) ... then average AO state during the upcoming winter will also be negative (positive); although the classification model is stronger ... i.e., lower false alarm rate ... for the predictor's month with a negative sign than positive.

Conclusion:  If NOV's AO is negative ... chances are good the AO state will average negative during D-J-F period.

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Period-of-record AO data here.

Winter '16 / '17 - North Atlantic Oscillation (NAO) Analog Verification

The analog forecasting technique seeks similarities to the NAO state in the run-up to the coming winter with NAO run-up states of winters past. 

The NEWxSFC method ranks analog years by their the sum of square errors (SSE) statistic.
Lower SSE errors ==> stronger analog
Constraining the number of analog winters for analysis to five is arbitrary.

North Atlantic Oscillation (NAO) Index Analog Forecast Verification

In the run-up to Winter '16 / '17 ... the leading analog was '08 / '09 followed by '51 / '52 ... '54 / '55 ... '74 / '75 ... and '11 / '12.  A qualitative assessment of the forecast's accuracy would rate the top four analog as 'poor' ... IOW ... useless.

Winter '08 / '09 NAO was negative to neutral trending positive into MAR; whereas Winter '16 / '17 was weakly positive trending moderate.  The closest analog ... on the basis of the NAO remaining positive throughout the three-month forecast period ... was ranked last ('11 / '12).

Conclusion:  Winter '16 / '17 NAO analogs showed little ... if any ... skill.

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An alternative forecasting technique looks at the NAO's sign for any calendar-year's month preceding the pending winter as a potential leading indicator of the NAO's sign for D-J-F period.

Results from a chi-square 'test for independence' infers a statistically significant relationship ... at the 95% confidence level and a p-value < 0.05 ... between NOV's NAO sign and NAO's sign of the upcoming D-J-F period.  IOW ... if NOV's NAO is negative (positive) ... then the average NAO state during the upcoming winter will also be negative (positive); although the classification model is stronger ... i.e., lower false alarm rate ... for the predictor's month with a positive signs than negative.

Conclusion:  If NOV's NAO is positive ... chances are good the NAO state will average positive during the D-J-F period.

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Period-of-record NAO data here.

Winter '16 / '17 - 18th Annual 'Regular Season' Snowfall Forecast Contest: FINAL Results

Four contest-worthy storms this season.  Tied with Winter '05 / '06 for 15th place.
Under the ‘two-thirds’ rule … forecasters who entered at least THREE forecasts are included in this season's FINAL standings..

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Top 5 Forecasts (Error statistic:  SUMSQ)
SUMSQ is the primary measure of forecaster skill (lower the better).
Accounts for the magnitude and distribution of the storm-total snowfall for all stations.

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Top 5 Forecasts (Error statistic:  Total Absolute Error - TAE)
TAE is the secondary measure of forecaster skill (lower the better).
Accounts for the magnitude of snowfall at each station.

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Top 5 Forecasts (Error statistic:  RSQ)
RSQ is a supplementary measure of forecaster skill (higher the better).
Accounts for how well the variability of the observed snowfall was accounted for by the forecast.


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Average Z-scores for Forecasters who submitted entries for all four snow storms.

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Winter '16 / '17 was only the third season without a JAN snow storm.

 

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Hope to see y'all again next winter.

Winter '16 / '17 - 18th Annual 'Regular Season' Snowfall Forecast Contest: The End is Nigh

Central Park ... NYC
19-FEB-41

Despite our longing for one more contest-worthy snow storm ... the long wave pattern shows little inclination to alter its ridiculously stubborn regime of processing 'all' SFC LOWs through the Great Lakes region.

Sure hasn/t been a great season for nor'easters in general or nor'easters climbing the coast from low latitudes specifically.

Most seasons ... it/s all said and done by early MAR.
Average date of the last 4" or greater snowfall:
CAR 23-MAR
BGR 15-MAR
PWM 08-MAR
ORH 07-MAR
BTV 06-MAR
CON 06-MAR
ALB 06-MAR
BGM 06-MAR
BOS 25-FEB
BDL 24-FEB

However ... there are exceptions.
Latest date of the last 4" or greater snowfall:
CAR 16-MAY
PWM 11-MAY
CON 10-MAY
ALB 10-MAY
ORH 09-MAY
BGR 24-APR
BTV 23-APR
BGM 22-APR
BDL 21-APR
BOS 10-APR

Source:
NOWData http://www.nws.noaa.gov/climate/index.php

The end of the Winter '16 / '17 snowfall forecasting season appears nigh.
All else equal ... the season will close on SAT ... 15-APR.

Winter '16 / '17 - 16th Annual 'Season-total' Snowfall Forecast Contest: FINAL Results

Complete station-by-station forecaster verifications at the Contest/s web site here.

Two perfect forecasts
Donald Rosenfeld 100" @ CAR
Mitchel Volk 15" @ PHL

Near misses
Jessica_wxgirl 0.05" error @ RIC (7.2")
Shillelagh and Jessica_wxgirl 0.1" error @ MDT (23.9")
donsutherland1 0.1" error @ ORH (75.4")
MillVillWx 0.2" error @ ALB (58.3")
kevinmyatt 0.2" error @ NYC (30.2")
weathermbug ... TQ ... and DAROOSTA 0.2" error @ SBY (9.8")
Herb @MAWS and weathermbug 0.2" error @ ORF (5.4")
snowman 0.3" error @ BTV (91.7") and 0.2" error @ EWR (31.4")
Donald Rosenfeld 0.5" error @ BGM (104.5")

Season-total snowfall from all stations (1041") came in 14% above the period-of-record normal (914").  Winter '16 / '17 ranks 6th highest among other Contest years since winter '04 / '05 ... the season when BGR and BGM were added to the station list. 

Winter '16 / '17 - Season-total Snowfall Forecast Contest: Observed Snowfall Station Summary

New England FTW!

 

Winter '16 / '17 - Season-total Snowfall Forecast Contest: MAR totals

Station snowfall summary for MAR-17.
Rank ordered by percent of monthly normal.

Station snowfall summary for Winter '16 / '17 - Season-to-date snowfall through MAR

Green ==> 75th percentile
White ==> 50th percentile
Red ==> 25th percentile
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Teleconnection indexes and month-over trend (updated as they become available)
AO:  1.365⇧
NAO:  0.74⇩
PDO:  0.74⇧
QBO:  14.35⇩
SOI:  5.1⇧

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Winter '16 / '17 - Last Gasp?

Philly

THU and FRI/s snowfall over our northern forecast stations may have been this winter/s last gasp for a contest-worthy snow storm.

Station / NWS mid-range forecast (") / STP (")
ALB / 3.5 / 1.8
BDL / 0 / 1
BTV / 2.5 / 2.5
ORH / 5 / 1.5
BOS / 5 / 0.6
CON / 10 / 5.7
PWM / 5 / 3

Four measly stations (five if you include the upper limit at ALB) were expected to see more than nuisance snowfalls.   In the end ... but one came through.

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Will keep the window open a little longer for the possibility for one last snow storm.

Over the forecasting contest/s 18 seasons ... there have been five contest snow storms in April ... the last one coming in 2011.  The return period is 4.5 years ... so we're 'overdue' for another.  If not ... the 'Regular' season will end with four snow storms (ranked 15th; top-ranked seasons:  '02 / '03 and '03 / '04 with 10 storms each).

Winter '16 / '17 - Temperature Departure from Normal: Progress Report

UPDATED for MAR anomalies:

  

 

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Cohen has some ground to make up in the east.

 

Will FEB offer a lifeline?

CFSv2 image courtesy WxAmerica