Winter Storms by Paul Kocin Winter Storm Expert The Weather Channel and Dr' Gerry Bell Climate Predi

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Winter StormsbyPaul Kocin Winter Storm
ExpertThe Weather Channel and Dr. Gerry
BellClimate Prediction Center
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Outline

• Winter Weather Impacts
• Winter Forecast Issues
• Northeastern U.S. Snowfall Impact Scale
• Climate factors influencing winter storms

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Winter Weather Impacts
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Each year, automobile accidents claim an
incredible amount of lives, cause injuries and
property damage.
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• The average/year of auto accidents
• 41,000 deaths,
• 3 million injuries,
• billions in damage.
• About 15 is weather-related

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• Weather related
• 7,000 deaths
• 800,000 injuries
• and billions of dollars in damage per year!

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• Adverse weather is associated with over 1.5
  million auto crashes per year.

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• Snow and ice make up a significant component of
  the dangers posed to transportation nationwide.

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• Examples In 2001
• 5400 deaths linked to rain-slicked roads
• 1100 deaths linked to snow and ice
• 670 deaths linked to fog
• Dept. of transportation cost estimates
• Injuries, loss of life, and property damage cost
  an average of 42 billion dollars annually just
  for snow and ice!

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Winter Forecast Issues
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• Winter forecast issues
• Precipitation type forecasts can be very
  difficult, especially a day or more into the
  future
• Rain vs freezing rain vs sleet vs
  snow
• Model forecast uncertainty
• Different models can often show
  significantly different forecasts beyond a few
  days.

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The main issue rain vs freezing rain vs sleet
vs snow
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• Problems with forecasting heavy snow
• It often occurs close to the rain/snow line
• It sometimes occurs close to the snow/ no snow
  line
• 50-mile errors in location produce big problems!

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Predictability Some storms are easy. Affect
one small region its well forecast Life is
GREAT Most storms are widespread, multi-day,
multi-form events..forecasts can be good one
place, Lousy others
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• More predictability
• Whether big or small, winter storm predictability
  is very variable.
• Some winter storms are amenable to prediction
  even several days in advance
• Other winter storms seem to be unpredictable even
  up to the day of the event

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Mean 4.80
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5 Top Ranked Snowfall Events

• Rank DATE NESIS
• 1 12-14 MAR 1993 12.52
• 2 6-8 JAN 1996 11.54
• 3 15-18 FEB 2003 8.91
• 4 11-14 MAR 1888 8.34
• 5 11-14 FEB 1899 8.11

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Northeast Snowfall Impact Scale (NESIS)
Paul J. Kocin Louis Uccellini The Weather
Channel NWS/NCEP
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Fujita and Saffir-Simpson Scales

• Measure potential for
• DESTRUCTION to property
• and loss of life from
• tornadoes and hurricanes

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NESIS

• Measures potential for human and economic
  DISRUPTION
• Categories (1 thru 5)

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SNOWSTORM IMPACT DUE TO

• SNOWFALL
• WIND SPEED
• TEMPERATURE
• DURATION
• SNOWFALL RATES
• STORM INTENSITY
• GROUND TEMPERATURES

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What NESIS is

• A measure that is based on the integrated effects
  of storm snowfall in the Northeast United States

• Based on areal coverage of snowfall amounts and
  population affected

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• LOOKED AT 30 CASES
• 1950-2000
• CONTOURED SNOWFALL
• at 4, 10 and at
• 20 intervals
• THOSE CONTOURS
• REPRESENT
• (1) an AREA
• (2) an AFFECTED POPULATION

Feb 1978
Mar 1993
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Mostly 4-10, small 10
NESIS VALUES Close to 1
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Small 4, Larger area of 10, small 20
NESIS VALUES Close to 3
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Even larger area of 4, 10, 20
NESIS VALUES Greater than 8
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NESIS CATEGORIES

• CATEGORY NESIS VALUES of CASES DESCRIPTION
• 1 1 2.499 23 NOTABLE
• 2 2.5 - 3.99 22 SIGNIFICANT
• 3 4 5.99 16 MAJOR
• 4 6 - 9.99 7 CRIPPLING
• 5 10.0 2 EXTREME

Being tested at NCDC for possible NWS
operational use
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Climate Factors Influencing Winter Storms1. El
Niño/ La Niña cycle2. North Atlantic Oscillation

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El Niño and La Niña
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SST(C) and Departures
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28oC is approximate threshold for deep tropical
convection
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ENSO Tropical Rainfall
EL Niño Enhanced Convection
La Niña suppressed convection
El Niño Tropical convection, jet stream extended
eastward La Niña Tropical convection, jet stream
retracted westward
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North Atlantic Oscillation (NAO)
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NAO Air Pressure and Winds at 30,000 ft
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1980s- 2001
1950s-1960s
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Positive (warm) Phase of Wintertime NAO
Temperature Precipitation
Warmer
Colder
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NAO DJF Time Series
50 55 60 65 70 75 80
85 90 95 00
Negative 1950s-1960s Stronger Hudson Bay
Low More Arctic outbreaks Cooler Temperatures
Positive 1980s-present Weaker Hudson Bay
Low Arctic air confined to Canada Milder
Temperatures
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El Niño NAOTemperature Composites
Moderate-to-Strong El Niños
Negative NAO Cooler in SE, Mid-Atlantic, NE
Positive NAO Warmer in SE, Mid-Atlantic, NE
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Negative NAO establishes cold air regime and
increases snow threat. Several major Northeast
snowstorms have occurred during strong - NAO
episodes
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Daily NAO Index
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Summary

• Winter Weather Impacts are significant.
• Winter storm forecasting remains a challenge,
  especially Rain/ snow line and snow/ no snow
  line.
• Northeastern U.S. Snowfall Impact Scale (NESIS)
  may be useful scale for categorizing winter
  storms and their impacts.
• Climate factors influence winter storms and
  snowfall throughout the U.S.
• Also cause year-to-year and multi-decadal cycles
  in winter storm activity.