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Winter Storms
by
Paul Kocin Winter Storm Expert
The Weather Channel
and
Dr. Gerry BellClimate Prediction Center
Outline1. Winter Weather Impacts2. Winter Forecast Issues3. Northeastern U.S. Snowfall Impact Scale4. Climate factors influencing winter storms
Each year, automobile accidents claim an incredible amount of lives, cause injuries and
property damage.
The average/year of auto accidents:
– 41,000 deaths,
– 3 million injuries,
– billions in damage.
– About 15% is weather-related
• 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!
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.
Problems with forecasting heavy snow
o It often occurs close to the rain/snow lineo It sometimes occurs close to the snow/ no
snow lineo 50-mile errors in location produce big
problems!
Predictability
Some storms are easy……….Affect one small region – it’s well forecastLife is GREAT
Most storms are widespread, multi-day, multi-form events…………..forecasts can be good one place,
Lousy others
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
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
Northeast Snowfall Impact
Scale (NESIS)
Paul J. Kocin & Louis UccelliniThe Weather Channel & NWS/NCEP
• Measure potential for DESTRUCTION to
property and loss of life from tornadoes and
hurricanes
Fujita and Saffir-Simpson Scales
• SNOWFALL• WIND SPEED• TEMPERATURE• DURATION• SNOWFALL RATES• STORM INTENSITY• GROUND TEMPERATURES
SNOWSTORM IMPACT DUE TO:
• A measure that is based on the integrated effects of storm snowfall in the Northeast United States
What NESIS is
• Based on areal coverage of snowfall amounts and population affected
• LOOKED AT 30 CASES – 1950-2000
• CONTOURED SNOWFALL at 4”, 10” and at20” intervals
• THOSE CONTOURS REPRESENT: (1) an AREA (2) an AFFECTED POPULATION
Feb 1978
Mar 1993
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
ENSO Tropical Rainfall
El Niño: Tropical convection, jet stream extended eastwardLa Niña: Tropical convection, jet stream retracted westward
EL NiñoEnhancedConvection
La Niñasuppressed convection
El Niño:•Extended Jet Stream•More zonal flow over U.S.•South shift of storm track•Weaker Hudson Bay Low•Fewer arctic outbreaks
La Niña:•Retracted Jet Stream •More meridional flow•Blocking over N. Pac•Stronger Hudson Bay Low•More arctic outbreaks
NAO Air Pressure and Winds at 30,000 ft
1980’s- 2001 1950’s-1960’s
++-
-
•NAO affects the Atlantic jet stream/ storm trackNAO affects the Atlantic jet stream/ storm track•Tremendous differences in poleward heat Tremendous differences in poleward heat transporttransport and temperatures at high latitudes and temperatures at high latitudes
NAO: DJF Time Series
50 55 60 65 70 75 80 85 90 95 00
Positive: 1980’s-presentWeaker Hudson Bay LowArctic air confined to CanadaMilder Temperatures
Negative: 1950’s-1960’sStronger Hudson Bay LowMore Arctic outbreaks Cooler Temperatures
Moderate-to-StrongEl Niño’s
Negative NAO:Cooler in SE,Mid-Atlantic, NE
Positive NAO:Warmer in SE, Mid-Atlantic, NE
El Niño – NAOTemperature Composites
Negative NAO establishes cold air regime and increases snow threat.Several major Northeast snowstorms have occurred during strong - NAO episodes
Summary1. Winter Weather Impacts are significant.
2. Winter storm forecasting remains a challenge, especially Rain/ snow line and snow/ no snow line.
3. Northeastern U.S. Snowfall Impact Scale (NESIS) may be useful scale for categorizing winter storms and their impacts.
4. Climate factors influence winter storms and snowfall throughout the U.S.
5. Also cause year-to-year and multi-decadal cycles in winter storm activity.