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

Winter '10 / '11 - Snow Storm #1 - NYC-area Blizzard Conditions

03z SFC analysis

JFK and HPN (White Plains) get the brass ring.  Other surrounding stations came close but failed the three-hour restricted visibility criterion.

Blizzards are high-wind storms where falling or blowing snow severely restricts the surface visibility for a period of three hours or more.

The blizzard began at JFK at 0151z (8:51 PM EST). The hour's METAR carries 0SM which is the tower visibility. SFC visibility is reported in the remarks as 1/8SM.

The wind was at or above the 30 kt threshold before and after the visibility condition was met. Blizzard conditions prevailed for three hours until 0451z (11:51 PM EST) when the SFC visibility improved to 1/4SM.

KJFK 270051Z 36029G38KT 1/4SM SN FZFG BLSN VV002
KJFK 270151Z 34034G42KT 0SM SN FZFG BLSN VV001 SFC VIS 1/8
KJFK 270251Z 34037G49KT 0SM SN FZFG BLSN VV001 SFC VSBY 1/8
KJFK 270351Z 34035G49KT 0SM SN FZFG BLSN VV001 SFC VIS 1/8
KJFK 270451Z 33031G44KT 1/8SM SN FZFG BLSN VV004 SFC VIS 1/4
KJFK 270459Z 34029G42KT 1/8SM SN FZFG BLSN VV005 SFC VIS 1/4

Similar story at HPN...
KHPN 270056Z 34024G32KT 1/4SM SN BLSN VV002
KHPN 270156Z 34030G41KT 0SM SN BLSN VV002
KHPN 270256Z 33028G45KT 0SM +SN BLSN VV001
KHPN 270356Z 33032G44KT 0SM +SN BLSN VV001
KHPN 270456Z 33034G48KT 0SM +SN BLSN VV001
KHPN 270556Z 33028G42KT 0SM +SN BLSN VV001
KHPN 270656Z 33030G43KT 3/4SM +SN BLSN VV002

Blizzard conditions began in White Plains at 8:56 PM (0156z) and ended at 1:56 AM (0656z)...lasting two hours longer than JFK.

These was a similar storm sixty-three years ago to the day (requires free Djvu plug-in).

Winter '10 / '11 - Snow Storm #1 - Snow Melt Water

NYC/s 8th Avenue
27-DEC-47

ACY...EWR...and ORF observed not only record-setting snowfalls yesterday but also impressive snow melt water.  Not as generous as the historic 26-DEC-47 storm where 2.53" of melt water was measured in NYC from the 26" snowfall.

ACY - 1.60"
EWR - 1.23" (1.06")
ORF - 1.22"

SN:H2O
ACY - 10.9:1
EWR - 14.2:1 16.7:1
ORF - 11:1


Updated 12/29 to revise EWR data.

Winter '10 / '11 - Snow Storm #1 - OKX - 0z SkewT-logP

Potent sounding out of OKX tonight.

The rawinsonde's initial low-level flight drifted to the SW over open waters before veering toward Newark...NJ (EWR) and continuing to the north across western New England.  EWR reported TSSN around the time of OKX's 0z balloon flight.

There's a deep...saturated moist layer between the SFC and 600 mb with 50 mb of conditional instability sitting on top.

The specific humidity in the crystal factory @700 mb is 4g/kg or more which can easily support snowfall rates over 1" / hr.  Note the excellent WAA nose @ 700 mb forced strongly by a 40 kt SE wind.

Cloud-tops located near 600 mb (~14K' AGL) where the saturated air temperature is < -15°C ==> perfect conditions for stellar dendrites!

Sounding courtesy NOAA's Storm Prediction Center

Winter '10 / '11 - Snow Storm #1 - Countdown to Blizzard Conditions

Common usage of the term 'blizzard' has come to mean excessive snowfall when in fact...a blizzard is a high-wind event (sustained wind or frequent gusts > 29 kts) that causes a reduction in surface visibility to less than 1/4 SM for at least three hours.

Blizzards are truely rare birds in the eastern CONUS where winter storms usually fail the visibility duration criterion.  One such event may be in the offing tonight...as evidenced by these early observations.

SPECI KTEB 262326Z 36020G30KT 1/16SM R06/1200V1800FT +TSSN BLSN FZFG OVC001 M05/M07 A2943 RMK AO2 PK WND 35031/2258 TSB20 OCNL LTGICCC P0001 $

METAR KJFK 270151Z 34034G42KT 0SM R04R/1600V2200FT SN FZFG BLSN VV001 M06/M07 A2921 RMK AO2 PK WND 35048/0140 SFC VIS 1/8 PRESFR SLP891 SNINCR 1/6 P0003 T10561072 $

METAR KEWR 270251Z 34025G35KT 1/8SM +SN BLSN VV001 M04/M06 A2926 RMK AO2 PK WND 35039/0221 TWR VIS 1/4 SLP909 SNINCR 3/14 P0018 60046 T10441056 58047 RVRNO $

METAR KHPN 270256Z 33028G45KT 0SM +SN BLSN VV001 M08/M11 A2918 RMK AO2 PK WND 34045/0250 SLP891 P0005 60013 T10831106 56058 $

Thunder snow (TSSN) reported at Tetterboro (KTEB)!

Winter '10 / '11 - Snow Storm #1 - The Forecasts

15 entries
3 Intern forecasters
3 Journeyman forecasters
9 Senior forecasters including Chief Forecaster Iralibov

Great turn-out and a great storm for the season opener.
All 27 stations in play making this an excellent test of synoptic-scale snowfall forecasting ability.

All forecasts have been posted to the Contest's web site. Follow the link from Winter '10 / '11 Storm Contest >  Forecasts > Storm #1.

Entries are ranked in ascending order by 'storm-total' snowfall.  Please check you entry for accuracy.

Broad range of expected storm-total snowfall...
Min: 80" (Weathermbug)
Max: 354" (Roger Smith)
Avg: 233"
Median: 254"
STD: 77"

Consensus heavy snowfall axis (+12") between PWM - BOS - PVD - ISP - JFK - EWR - BDR - BDL - ORH - CON - PWM.

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

Off-shore waters of GA starting to churn...

Wind picking up...gettin'gusty.
Pressure falling nicely now.