Appendix

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Appendix

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For the Encore:

NYC Blizzard (Dec 25-27, 2010)

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Radar/HPC Surface Analysis December 25-28, 2010

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NYC Blizzard Dec 25 – 27, 2010

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Snowfall Totals

Guidance from 12Z December 22 - Wednesday

Forecast uncertainty led to inaction that increased the overall impact of the

storm

Observed – BlueECMWF – RedGFS - Green

7Guidance from 12Z December 24 - Friday

Observed – Blue12Z ECMWF – Red12Z GFS – Green00Z ECMWF - Brown

Surface Analysis Seven day forecastValid 12Z December 27, 2010

Surface Analysis Six day forecastValid 12Z December 27, 2010

Surface Analysis Five day forecastValid 12Z December 27, 2010

Surface Analysis Four day forecastValid 12Z December 27, 2010

Surface AnalysisValid 12Z December 27, 2010

Forecast Issued 24 December 2010

Three day forecast

Surface Analysis Two day forecastValid 12Z December 27, 2010

Surface Analysis One day forecastValid 12Z December 27, 2010

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3 daysprior

SREF/GEFS Forecasts for Dec 26, 2010: NYC Blizzard

2 daysprior

1 day prior

• Favorable Jet-Streak Circulation Pattern

• Radar Simulation of Snow Bands*

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Short Term Forecasts Point to Potential Heavy Snowfall in NYC and

Surrounding Areas

* 4km NMMB will be operational for next winter

Model Forecasts: 250 MBCoupled Jets (00Z Mon Dec 28 2010)

GFS 24 Hour Forecast

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HPC SFC Map Observed RadarNAM 4km Reflectivity

18 ZDec 26

00 ZDec 27

06 ZDec 27

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30hr fcst

Model Forecast: Simulated Reflectivity33 hour Reflectivity Loop

(03 UTC 26 Dec to 12 UTC 27 Dec)

NAM (run on 00Z Dec 26)Simulated Reflectivity experimental 4 km NMMB

model (to become operational this summer)

*

December 26-27, 2010

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• Potential for major east coast storm highlighted 5 days in advance• Low confidence about model predictions – especially track forecasts – until late December 24• Blizzard warning issued for NYC at 4PM Saturday, December 25 (14 hours prior to onset)• By December 24-25, special effort made to reach out to Emergency managers and airline industry prior to onset of heavy snow in Northeast corridor/NYC• Airline industry takes action• Snow emergency not declared in NYC• NYC/NJ/West CT gets buried by 2+ feet of snow with 50+ mph winds

• Airlines/airports are prepared for crippling event– Cancel thousands of flights– Attempt to mitigate impact on

national and international flight operations

– Fully recover in 3-4 days

• NYC does not declare snow emergency despite blizzard warning – results in major gridlock within city

Impacts:Forecast for 26-27 December 2010

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New York City Report:Preliminary Review of the City’s Response to the

December 2010 Blizzard - Report and Recommendations

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• From Introduction – “On December 26, 2010, a blizzard struck New York City and surrounding areas. Though earlier forecasts had called for only a light to moderate snow falls, the National Weather Service issued a blizzard warning at 3:55 PM on December 25th. At that time, between 11 and 16 inches of snow were predicted, along with high winds and low visibility. Even this forecast underestimated the storm’s ferocity. ”

• Third of six key problems – “Insufficient and delayed deployment of City assets. The weather forecast for the storm got significantly worse rather quickly, culminating in a blizzard warning issued at 3:55pm on Christmas Day. Due to the late change in the forecast, as well as the fact that DSNY has adeptly handled large snowfalls so many times previously without assistance, agencies that are not typically involved in snow removal—such as the Taxi and Limousine Commission --were not mobilized expeditiously.”