North Atlantic Oscillation - Trending South

Blue line is NAO's five-year moving average for meteorological winter (D-J-F) which at the end of last winter dipped below zero for the first time since 1982.

Note how the 5-yr moving average was negative for 21 years between 1953 and 1973...then a nine-year transition period when the sign flip-flopped after holding serve one way or the other briefly for four or five years...followed by 27 years where the NAO's moving average was positive.

Might this herald the start of a protracted...multi-decadal period of negative winter-time NAOs?

Source

In other news...DEC-10 NAO came in at -1.85...marking the 15th consecutive month it's been below zero and the 3rd lowest index value for December since 1950.  Second-lowest December was 1963.  All-time record minimum is DEC-09.

Closest analog year based on least-squares analysis is 1968 / 1969 which was +ENSO...-QBO...and -PDO.

Second-closest analog year based on least-squares analysis is 1977 / 1978 which was +ENSO...+QBO (month-one of west phase)...and mixed PDO.

Winter '10 / '11 - Snow Storm #1 - Final Results - UPDATE

F6 bulletins (CXUS51 - PRELIMINARY LOCAL CLIMATOLOGICAL DATA) for several forecast stations now have data entries or have been revised.  Forecast verifications have been updated to reflect the new information.

Original / Revised Station Data
BGR - 10.3" / 10.8"
PWM - 8.5" / 7.5"
CON - 6.6" / 7.1"
ORH - 17" / 12.7"
ACY - 19" / 20"

No change in the standings for the top three forecasts; however...'ejbauers' and 'Shillelagh' swap 4th and 5th places...'TQ' and 'iralibov' move ahead to 6th and 7th as 'weatherfella' drops to 8th...and 'snowman' jumps over 'Newa' from 11th to 10th after updating the results with new or amended verification data.
---
Original Results
-1.277 1 Senior donsutherland1
-1.033 2 Senior Donald Rosenfeld
-0.929 3 Senior Mitchel Volk
-0.880 4 Intern ejbauers
-0.823 5 Senior Shillelagh
-0.509 6 Journeyman weathafella
-0.488 7 Senior TQ
-0.455 8 Chief iralibov
0.040 9 Journeyman WeatherT
0.179 10 Senior Newa
0.313 11 Senior snowman
0.922 12 Intern Roger Smith
1.331 13 Senior defman27
1.721 14 Journeyman MarkHofmann
1.889 15 Intern Weathermbug

---
Revised Results
-1.274 1 Senior donsutherland1
-1.013 2 Senior Donald Rosenfeld
-0.986 3 Senior Mitchel Volk
-0.868 4 Senior Shillelagh
-0.866 5 Intern ejbauers
-0.512 6 Senior TQ
-0.466 7 Chief iralibov
-0.393 8 Journeyman weathafella
-0.021 9 Journeyman WeatherT
0.246 10 Senior snowman
0.263 11 Senior Newa
1.061 12 Intern Roger Smith
1.233 13 Senior defman27
1.795 14 Journeyman MarkHofmann
1.802 15 Intern Weathermbug

---
The Forecast Verifcation page at the Contest web site will be updated but not the storm Summary page.

Winter '10 / '11 - Coastal Teaser #2

Look familiar?

GooFuS has a coastal storm on the 7th as well; however...its genesis is in the northern stream leaving the SW bowling ball behind.

Graphics courtesty Plymouth State Wx Center.

Winter '10 / '11 - Snow Storm #1 - Final Results

1st
Donsutherland1

SUMSQ: 385.44

SUMSQ Z: -1.277

STP: 3.45 (1)

TAE: 81.25 (1)

AAE: 3.01 (1)

2nd
Donald Rosenfeld

SUMSQ: 526.03

SUMSQ Z: -1.033

STP: 12.85 (4)

TAE: 95.85 (3)

AAE: 3.55 (3)

3rd
Mitchel Volk

SUMSQ: 585.48

SUMSQ Z: -0.929

STP: 20.65 (5)

TAE: 97.35 (4)

AAE: 3.61 (4)

Honorable mention
EJBauers
SUMSQ: 614.01
SUMSQ Z: -0.880
STP: 51.45 (8)
TAE: 104.25 (5)
AAE: 3.86 (5)

SUMSQ: sum of square errors
STP: storm total precipitation error
TAE: total absolute error
AAE: average absolute error
(number):  category ranking

Full forecast verification and summary at the Contest web site.

Winter '10 / '11 - Snow Storm #1 - Snow Cover

Image courtesy NASA's Terra satellite.

Close-up of the NE here. 

Winter '10 / '11 - Snow Storm #1 - Teleconnections

Arctic and North Atlantic Oscillations have been below zero...with few exceptions...since mid-NOV thanks to strong hi-latitude blocking over the North Atlantic and Pacific Oceans.

Likewise...the PNA.

Winter '10 / '11 - Snow Storm #1 - Storm Evolution at 500 MB

Short-wave trough comes ashore in southern CA on 23-DEC-10...undercuts the short-wave ridge axis over the Rockies on the 24th...then phases with a northern stream short-wave in over the lower MS River Valley.  Note the strong cold air advection (CAA) driving the northern stream short-wave at 00z on the 26th prior to the phasing which causes the wavelength to shorten and amplify.

The mid-level circulation begins to close off 12 hours later at 12z on the 26th followed by a 12-hour 180 m height-fall between 00z and 12z on the 27th.  Large height-falls at 500 MB indicate strong cooling aloft associated with strong upward vertical motion (UVM).

Stream-phasing was one element behind the flip-flopping of NWP solutions in the run-up to the snow storm.

Graphics courtesy University of Wyoming

Winter '10 / '11 - Snow Storm #1 - Preliminary Verification

Preliminary storm-total snowfalls for Sunday and Monday from CDUS41...CXUS51...and PNS.

No snowfall data in the NWS climate bulletins for SBY.  Verifying storm-total snowfall is the average of two vicinity station reports from AKQPNS.  This station's snowfall reporting fell into a black hole last year and has yet to reappear.

Storm-total snowfall for CON looks suspicious given its relatively low water equivalent; however...vicinity reports carried in BOXPNS suggest the amount is accurate.

Twelve new daily records.

SUN...26-DEC-10
ISP - 11.3" (1"; 2003)
JFK - 10.5" (4.4"; 1969)
ACY - 17.4" (0.2"; 1970)
ORF - 13.4" (5"; 2004)
RDU - 6.7" (T; 2004)

MON....27-DEC-10
CAR - 6.2" (5.4"; 2005)
BGR - 10.3" (4.1"; 1947)
BOS - 8.3" (5.7"; 1894)
BDR - 4" (1.1"; 1963)
BDL - 7" (4.7"; 1944)
JFK - 5.1" (3.2"; 1984)
EWR - 6.5" (4.7"; 1984)

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

Final results and storm summary by WED evening.

Winter '10 / '11 - Arctic Oscillation

Beautiful imagery from NASA/s Earth Observatory showing surface air temperature anomalies resulting from persistently negative Arctic Oscillation.  Red (blue) areas are warm (cold) surface air temperature anomalies.  "This image shows the temperature of the land surface for December 3-10, 2010 compared to the average temperature for the same period between 2002 and 2009."

The monthly Arctic Oscillation index has been below zero...15 out of 18 months since JUN-09.  The AO fell to an all time low of -4.266 in FEB-10.  Last winter's D-J-F average was -2.587.

Persistent HIGH pressure...often associated with a weak polar vortex (PV)...over the north pole allows arctic air to drain into low latitudes.  Daily AO values have been negative since mid-NOV.  This goes against type considering the QBO is in its westerly phase where the AO is typically positive...a consequence of a strong...cold PV.

Winter '10 / '11 - Snow Storm #1 - NYC/s NWS MET Fails Blizzard Test

From the NYT...

"But for all its bluster and powder, the monster storm was technically a blizzard only outside of Manhattan. The winds in Central Park topped out at 36 miles per hour but were not sustained over a period of three consecutive hours, nor was the visibility under a quarter of a mile for that period — both requirements to qualify as a blizzard.

“We didn’t quite make the criteria in Central Park,” said Matt Scalora, a meteorologist with the National Weather Service in Central Park. “But we did meet the criteria at J.F.K. Airport and La Guardia,” he added."

Blizzard conditions were observed at JFK but not at LGA where the SFC visibility never went below 1/4SM.

KLGA 262346Z 35024G33KT 1/4SM +SN BLSN VV001
KLGA 262351Z 35026G37KT 1/4SM +SN BLSN VV001
KLGA 270051Z 35023G38KT 1/4SM +SN BLSN VV001
KLGA 270151Z 35026G43KT 1/4SM SN BLSN VV001
KLGA 270251Z 34025G38KT 1/4SM SN BLSN VV001
KLGA 270351Z 34027G40KT 1/4SM SN BLSN VV001
KLGA 270451Z 33031G40KT 1/4SM SN BLSN VV001