Winter '09 / '10 - White Xmas

Winter '09 / '10 - WSI - December Update 2

Dr. Todd Crawford - WSI seasonal forecaster:

""The combination of the current El Niño event, cold north Pacific, and weakened stratospheric vortex are favorable for a continuation of widespread below-normal temperatures across the US for the upcoming season"...

""There may be a relaxation of the current cold pattern in the Northeast during January, followed by a return to more consistent cold in February and March."

"In January, WSI predicts regional temperature anomalies as follows:
Northeast - Warmer than normal, except PA/NJ/DE

"In February, WSI sees the monthly breakdown as:
Northeast - Colder than normal

"In March, WSI forecasts:
Northeast - Colder than normal"

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The stratospheric vortex began to weaken and split late last month continuing into early DEC; however...the two PV circulations have since merged and the upper level anticyclone has dissipated.  The effects of the weakened PV took about three weeks to reach the bottom of the troposphere...as evidenced by near-record low AO index.

Today/s 10 mb geo-potential height / air temperature analysis (courtesy U of WY) shows a strong... consolidated PV centered near the pole.

Winter '09 / '10 - Snow Storm #1 - Final Results

NEWxSFC Chief forecaster donsutherland1 picked up where he left off last winter with another top-ranked synoptic-scale snowfall forecast.

His 27 station forecasts verified with 344.2 SUMSQ error points (Z-Score = -0.915)...a 67% improvement over the average error of 1056".  The 220" storm-total precipitation (STP) forecast for all stations came within 5% of the observed 213.4" snowfall.

Donsutherland1/s issued perfect forecasts @ BOS and BGM.

Congratulations donsutherland1!

2nd Place:  Donald Rosenfeld (SUMSQ error: 372.9"; Z-score:  -0.878)

3rd Place:  Newa2010 (379.16"; -0.870)
Honorable Mention:  Herb @ MAWS (383.2; -0.865)

Full forecast verification and results summary here.

Winter '09 / '10 - Arctic Oscillation

The Arctic Oscillation (AO) was headed toward near-record levels during the past weekend while an historic storm buried many locations in the mid-Atlantic and southern New England with record snowfalls. 

A minor stratospheric warming event preceded the east coast snow storm by three-to-four weeks. The polar vortex (PV) weakened after splitting in two during late NOV and early DEC...as reported on the NEWxSFC web log here...here...and here.

The PV/s stronger half shifted from the eHEMI to wHEMI...where opposing flow between the two circulations created weak ridging near the pole.  With time...the ridging aloft made its way to the surface where an arctic anti-cyclone pushed the AO to levels seldom seen.

The last time the AO was less than or equal to 21-DEC-09/s -5.668 value was over 20 years ago on 01-JAN-85.

The AO has been this low...or lower...on just 15 days since modern record-keeping began in 1950  (NOV-59, JUN-64, JUL-64, MAR-70, JAN-77, JAN-85).  The odds of an AO index value at or below -5.668 are 1 in 1460 (0.07%).

The record negative value of -7.433 was set 15-JAN-77 during a borderline +ENSO (MEI = 0.484)... strong +PDO (1.65)...and an east QBO (-14.91).

Winter '09 / '10 - Snow Storm #1 - Preliminary Verification

Preliminary storm-total snowfalls for Saturday and Sunday from CDUS41...PNS...and CF6 bulletins.

Nine new daily records.

SAT...19-DEC-09
ISP - 9.6" (5.6"; 1995)
PHL - 22.5" (9.2"; 1945)
ACY - 11.4" (4.5"; 1979)
DCA - 15" (7"; 1945)

SUN...20-DEC-09
BOS - 10" (7.7"; 1995)
PVD - 14.3" (6.3; 1995)
ISP - 14.3" (4.2"; 1995)
JFK - 4.7" (3.8"; 1995)
EWR - 4.3" (3.2"; 1964)

Please report errors in Comments.

Final results and storm summary Tuesday evening.

Surface analysis:  19-DEC-1945.
Daily snowfall records last set in 1945...fell at PHL and DCA during Storm Day 1.  The 1945 Miller 'A' nor'easter originated in Galveston Bay...TX...then tracked NE to a position near HSE.

Surface analysis:  20-DEC-1995
Daily snowfall records set in 1995 at ISP...JFK...BOS...and PVD during Storm Day 2.  The 1995 MIller 'B' nor'easter formed near HSE...passing just south of the 'benchmark' at 40/70.

Winter '09 / '10 - Snow Storm #1 - ECMWF Verification

Outstanding NWP performance!
ECMWF/s 96-HR (4-day) Forecast

Miller-hybrid 996 mb surface LOW south of HSE.
Open 5H trof over OH river valley
Occluding 2ndary surface LOW over NE OH

Observed

Miller' A' 989 mb surface LOW due E HSE.

Closed 5H LOW over OH river valley

2ndary surface LOW over southern OH / NE KY

GooFuS didn/t have a clue...projecting the storm off-shore near the VA Capes...then out to sea.

Winter '09 / '10 - Snow Storm #1 - Blizzard Conditions

Blizzard conditions were observed at Islip...NY between 10:30 PM EST...19-DEC-09 through almost 2 AM EST...20-DEC-09.

Three conditions are needed for a blizzard:

1 - Visibility frequently less than 1/4 SM (< 1320')...

2 - Sustained wind speed or frequent gusts of 30 KTs (35 MPH) or higher...and

3 - Restricted visibility and high-wind conditions observed for at least three hours.

Note the METAR reports of SNINCR 3/xx (three inches-per-hour followed by the amount on the ground...rounded to closest whole number) in the 0456z...0556z...and 0656z observations (Sunday midnight - 3 AM EST)

SPECI KISP 200328Z 36017G27KT 1/8SM +SN BLSN FZFG VV001 M04/M07 A2955 RMK AO2 PK WND 01030/0300 P0001 $

METAR KISP 200356Z 36020G30KT 1/8SM +SN BLSN FZFG VV001 M04/M07 A2952 RMK AO2 PK WND 36031/0330 SLP998 SNINCR 1/7 P0001 T10441067 $

METAR KISP 200456Z 36019G30KT 1/16SM +SN BLSN FZFG VV001 M04/M07 A2949 RMK AO2 PK WND 01034/0441 SLP987 SNINCR 3/10 P0003 T10441067 410111050 $

METAR KISP 200556Z 36020G35KT 1/8SM +SN BLSN FZFG VV001 M04/M07 A2948 RMK AO2 PK WND 35035/0554 SLP985 931114 4/013 SNINCR 3/13 P0002 60013 T10441067 11039 21050 56023 $

METAR KISP 200656Z 35021G32KT 1/8SM +SN BLSN FZFG VV001 M04/M07 A2950 RMK AO2 PK WND 36032/0649 SLP989 SNINCR 3/15 P0003 T10441067 $

METAR KISP 200756Z 35016G22KT 1/4SM +SN FZFG BLSN VV002 M04/M07 A2953 RMK AO2 PK WND 36030/0717 SLP999 SNINCR 2/17 P0003 T10441067 $
 
Blizzards are wind storms where visibility is restricted by falling or blowing snow.
 
Blizzards defined here and here.

Winter '09 / '10 - Snow Storm #1 - Snow Cover

Snow cover as of 20-DEC-09 at 12z.  Heavy snow axis 18 - 21" runs through ROA - DCA - BWI - DOV - southern NJ - eastern LI.

Image courtesy NOHRSC

Winter '09 / '10 - Snow Storm #1 - The Forecasts

26 forecasters...including 10 rookies...issued 550 stations forecasts for this season/s inaugural snow storm.  Forecasts are ranked by storm total precipitation (STP) in ascending order.  Blue (red) values are in the 25th (75th) percentile.

Forecasts here.

Consensus heavy snowfall axis from IAD - DCA - BWI - PHL - EWR - JFK - ISP -ACY - IAD.

Amplifying flow regime evidenced by rising PNA and cold air source indicated by strongly negative values for NAO and AO.  Oscillations come on the heels of a minor stratospheric warming event that slowed and split the PV.  Arctic region surface pressure rose as the one piece of the PV moved from eHEMI to wHEMI...where opposing flow between the two circulations created weak ridging near the pole.

986 surface LOW over HSE SAT 19-DEC-09 at 12z crawls to a position abeam the southern end of Delmarva peninsula 12 hours later laying down a wide swath of heavy snow from VA to MD on its way to SNE.

Verification period ends 11:59 PM EST...SUN 20-DEC-09.  Preliminary storm-total snowfall totals will be posted the evening of MON 21-DEC-09.

Winter '09 / '10 - Early Snow...Cold Snap Hits NW Europe

"The iconic Eiffel Tower was closed to visitors, and train and bus services were delayed in many areas, as daytime temperatures dropped below zero for the first time in the year and black ice coated northern roads.

"Snow also fell in Britain, Germany, Belgium and the Netherlands and weather experts forecast worse to come, with disruption especially in Scotland and northern England.

"The northern Netherlands experienced the worst falls in four years, with snow up to 25 centimetres deep in places..."

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