Winter '14 / '15 - Weakening Polar Vortex ==> Sudden Stratospheric Warming: UPDATE 5

"Overall, the easterly winds descending into the lower tropical stratosphere is continually favorable for redirecting tropospheric waves anomalously poleward, which increases the odds of interaction with the stratospheric polar vortex and hence increases the chances of a SSW event this winter. (AER)

OBS

CPC - Stratosphere-Troposphere Monitoring

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First sign of sudden warming at 30 mb

30-hPa temperature change in a week in the Northern Hemisphere
The contour interval is 5 °C. The pink and light blue shadings indicate warming and cooling, respectively. The red shading denotes warming for values higher than 25 °C.

 

Tokyo Climate Center, Climate Prediction Division

 

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PROGS

NWP projecting a return to above-normal temperatures around mid-JAN.

Have they accounted for the effects from this SSW event?

Winter '14 / '15 - Weakening Polar Vortex ==> Sudden Stratospheric Warming: UPDATE 4

OBS

Expanding area at 10 mb over Siberia (red shading) where the one-week temperature change exceeds 25°C.

 

10-hPa temperature change in a week in the Northern Hemisphere

The contour interval is 5 °C. The pink and light blue shadings indicate warming and cooling, respectively. The red shading denotes warming for values higher than 25 °C.

 

Imagery courtesy Tokyo Climate Center, Climate Prediction Division

 

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PROGS

The 12z / 29-DEC-14 ECMWF suggests the 'split-vortices' SSW portion of the current event will peak between 03 / 06-JAN-15 followed by displacement. on D+10.

Deep-layer easterlies depicted on 03-JAN.
Short-lived daughter vortices appear briefly at the 475K level on 06-JAN.

Displacement

 

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SSW TYPES 

 

 

Winter '14 / '15 - Weakening Polar Vortex ==> Sudden Stratospheric Warming: UPDATE 3

Minor warming in progress INVOF Siberia.

 

10-hPa temperature change in a week in the Northern Hemisphere

The contour interval is 5 °C. The pink and light blue shadings indicate warming and cooling, respectively. The red shading denotes warming for values higher than 25 °C.

 

"A stratospheric warming is called 'minor' if a significant temperature increase is observed ([...] >= 25°C in a ... week or less) at any stratospheric level in any area of winter time hemisphere. The polar vortex is not broken down and the wind reversal from westerly to easterly is less extensive." (REF)

 

Imagery courtesy Tokyo Climate Center, Climate Prediction Division

Major warming appears imminent.

"Major SSWs occur when the westerly winds at 60N and 10 mb  reverse direction. A complete disruption of the polar vortex (PV) is observed.  The PV will either be split into daughter vortices ... or be displaced from its normal location over the pole." (WMO)

Winter '14 / '15 - Weakening Polar Vortex ==> Sudden Stratospheric Warming: UPDATE 2

The 12z / 25-DEC-14 run of the ECMWF continued its current campaign for a sudden stratospheric warming (SSW) event come JAN.

Progs suggest the birthing of daughter vortices around 04-JAN-15 induced by the upward propagation of a large tropospheric Rossby wave in a QBO-east environment.  A 'major' SSW event is indicated.

 

"A major SSW occurs when the 10 mb 60°N zonal mean zonal wind reverses from westerly to easterly and the 10 mb zonal mean temperature gradient increases poleward of 60°N." (.pdf)

 

Another view of the impeding split at the 475K level from a potential vorticity (NASA) perspective ... 

 

 

The downward propagation of the stratospheric easterly circulation (or a significant weakening of west wind) and the establishment of the Arctic Oscillation (AO) in its negative phase usually follows major SSW events.

Winter '14 / '15 - Weakening Polar Vortex ==> Sudden Stratospheric Warming: UPDATE 1

The 12z / 24-DEC-14 run of the ECMWF continued its current campaign for a sudden stratospheric warming event come JAN.

Latest progs point to a weakening and splitting of the stratospheric polar vortex (PV) ... a flip in the high-latitude deep-layer tropospheric flow from W-to-E ... and the ginning-up an anti-cyclonic circulation INVOF 90°N ... all of which point to the near-term development of a negative state for the Arctic Oscillation (AO) and all that implies.

Winter '14 / '15 - Weakening Polar Vortex ==> Sudden Stratospheric Warming

Output from the ECMWF 12z / 21-DEC-14 run shown below forecasts
1)  significant weakening of the PV from 145 KT at initialization to 50 KT on the 240-hr prog and
2)  beginnings of a PV reversal (mean easterly wind above 5 mb)
3)  maintenance of a strong sub-tropical jet (STJ)

"Pronounced weakenings of the NH wintertime stratospheric polar vortex tend to be followed by episodes of anomalously low surface air temperatures and increased frequency of occurrence of extreme cold events throughout densely populated regions such as eastern North America, northern Europe, and eastern Asia that persist for ~2 months."
REF:  http://www.nwra.com/resumes/baldwin/pubs/Thompsonetal_2002.pdf

QBO/s SUPPORTING ROLE 
Winters in a negative / easterly QBO regime favor PV weakening and subsequent SSW events.  In years with low solar sunspot activity ... the polar winter vortex also tends to be disturbed and weak when the QBO is easterly; however ... solar sunspot activity is neither high nor low.

FWIW 
Top three QBO analog years are 1972 ... 1958 ... and 2009.

1972/3 - strong el Nino
1958/9 - weak el Nino
2009/10 - moderate el Nino

QBO phases typically last ~13 months before reversal.
The QBO is seven months into its east phase through NOV-14 and will remain negative throughout this winter.

Winter '58 / '59 snowfall in the southern M-A was well above normal ... central M-A and NNE much below normal ...  and SNE below normal.

OUTLOOK
The time to propagate a SSW-induced west-to-east flow reversal from 10 mb to the near-surface is variable but averages ~3 weeks.  All else equal ... should the 12z 21-DEC-14 ECMWF perfect-prog verify ... the full effects associated with a persistently negative Arctic Oscillation (AO) would not be felt at the surface until late JAN at the earliest.

Winter '14 / '15 - Global Forecast System Wishing You a Very Merry Christmas

Winter '14 / '15 - November/s AO Predicts The State Of Winter/s AO

Does the sign of NOV/s Arctic Oscillation index (AO) of -0.530 have any predictive power for the sign of this winter/s AO?

The 2x2 contingency table below suggests it does.

At the 95% confidence level ... the Chi-square 'Test of Independence shows the negative sign of NOV/s AO and the AO sign for D-J-F are not independent but are related.  There/s a 2.8% probability the test indicates falsely they are not related.

Over the AO/s 64 year period-of-record ... the data shows when NOV is negative ... the winter/s AO will be also negative.

There/s also a statistically significant relationship between the negative sign of NOV/s AO and the sign of DEC/s AO.

False + ==> prediction is False
True + ==> prediction is True

AO Contingency
p = 0.028	Nov +	Nov -	Total
D-J-F +	15	8	23
D-J-F -	15	26	41
Total	30	34	64
True +	50%	24%	False +
False +	50%	76%	True +

Winter '14 / '15 - 14th Annual 'Season-total' Snowfall Forecast Contest: Forecast Summary

Good to see everyone for the 14th Annual NE.Wx 'Season-total' snowfall forecast contest.
Sixteen forecasters this year.
All veterans.

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As always, a wide range of forecasts with one lone forecaster/s season-total precipitation (STP) going under the NCDC period-of-record normal (P-O-R-N) season-total snowfall (934").

MIN STP:  866"
P-O-R-N:  934"
MAX STP:  1,546"
AVG STP:  1,175"
Median STP:  1,162"

Total number of station forecasts:  375
OVER:  307
UNDER:  67
P-O-R-N:  1

Forecasts in the table below are ranked in ascending order by sum-total snowfall for all stations.

Blue cells:  <= 25th percentile
Red cells:  >= 75th percentile
P-O-R-N is the Period of Record Normal.
CONSENSUS is the average of all forecasts.

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No majority opinion for UNDER snows anywhere.
Unanimous opinion for OVER @ BGR .... CON ... and BOS.

Largest AVG OVER
PHL (168%)
BDR (146%)
BGR ... SBY (142%)

OVER / UNDER forecasts
RDU (9 / 7)
BDL ... BGM ... EWR (11 / 5)
ORH ... MDT ... SBY ... ORF (12 / 4)

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These prizes for 1st place will be delivered post-paid right to the forecaster/s front door.

"The Snow Booklet" by Nolan J. Doesken and Arthur Judson
http://ccc.atmos.colostate.edu/snowbooklet.php

"Snow in America" by Bernard Mergan (hardcover)
http://artsbeat.blogs.nytimes.com/2009/03/02/snows-of-yesteryear/?_r=0

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

Winter '14 / '15 - ENSO Takes A Second Step Toward el Niño Event

Is it el Niño or is it el Noño?

DEFINE the BEGUINE
One definition holds the Oceanic Niño Index (ONI) has to:

... met +0.5°C threshold for five straight months of a 3-month running mean.  For historical purposes warm 'episodes' are defined when the threshold is met for a minimum of 5 consecutive over-lapping seasons.

Another holds North America's operational definitions for El Niño, based on the ONI index is:        

El Niño: A phenomenon in the equatorial Pacific Ocean characterized by a positive sea surface temperature departure from normal (for the 1971-2000 base period) in the Niño 3.4 region greater than or equal in magnitude to 0.5 degrees C (0.9 degrees Fahrenheit), averaged over three consecutive months.

WHAT'S THE EVIDENCE?
The latest SST anomaly (SSTa) for ENSO Region 3.4 from NOAA's Climate Prediction Center (CPC) is +1.0°C (26-NOV-14).  This brings the 13-week (i.e., three months) moving SSTa average in ENSO Region 3.4 to 0.58°C.

Last week/s 13-week ENSO Region 3.4 moving SSTa average of 0.54°C breached the 0.5°C threshold for North America's operational definition for El Niño.  The week previous:  +0.492°C.


ENSO Region 3.4 SSTa (BLUE) and 13-week SSTa Moving AVG (ORANGE)
JAN-10 to Present

WTF?

In spite of these developments ... what's the hold-up in recognizing the beginning of el Niño 2014?  It is b/c of how a 'month' is defined?

A month starts on the 1st and ends on the 30th or 31st (piss off FEB). 
Anyone think there's a Gregorian calendar hanging over ENSO Region 3.4?

 Just b/c the ENSO Region 3.4 SSTa havn't been above the +0.5°C threshold for three consecutive calendar months doesn't mean +ENSO hasn't started.  The 13-week moving average (i.e., 3-month) ENSO Region 3.4 average SSTa exceeded the el Nino threshold during the week of 19-NOV-14.


CPC/s foot-dragger report
ENSO: Recent Evolution, Current Status and Predictions (01-DEC-14)

Winter '14 / 15 - Arctic Oscillation Analysis and Forecasts

New blog devoted to the Arctic Oscillation (AO) ... Siberian snow cover ... and more authored by Atmospheric and Environmental Research's (AER) Judah Cohen and Jason Furtado.

Cohen ... et al ... discovered the strong correlation between the areal coverage ... advancement rate of Eurasia/s OCT snow cover and the character of northern hemisphere's winter as modulated by the AO.

Snow Advancement Index (SAI)

The chart reports a correlation index (r) of 0.810 indicating the AO and SAI often move in tandem. 

Squaring the correlation index gives the 'coefficient of determination'; a measure of how much of the variability of one (DJFM AO) is explained by the other (SAI). The SAI 'explains' 66% of DJFM/s AO variability.

 

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Cohen/s 2013 interview with the WAPO

Cohen/s 2014 interview with the WAPO

Snow cover data from Rutgers Global Snow Lab

 

 

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