Winter Weather (Paul Kocin)

8/7/2019 Winter Weather (Paul Kocin)

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Winter Storms

by

Paul Kocin

Winter Storm Expert

The Weather Channel

and

Dr. Gerry Bell

Climate Prediction Center


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Outline1. Winter Weather Impacts

2. Winter Forecast Issues

3. Northeastern U.S. Snowfall Impact Scale

4. 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 autocrashes per year.


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Snowandice make up a significant component ofthe

dangersposedtotransportationnationwide.


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Examples: In 2001

5400 deaths linked to rain-slicked roads 1100 deaths linked to snowand 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 snowand ice!


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Winter Forecast Issues


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Winter forecast issuesPrecipitation 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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Predictability

Some storms are easy.

Affect one small region its well forecast

Life is GREAT

Most storms are widespread, multi-day, multi-formevents..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 TopRankedSnowfall Events

Rank DATE NESIS

1 12-14 MAR1993 12.52 2 6-8 JAN 1996 11.54

3 15-18 FEB 2003 8.91

4 11-14 MAR1888 8.34

5 11-14 FEB 1899 8.11


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Nor

theas

tSnowfa

ll

Impact Scale

(NESIS)

Paul J. Kocin & LouisUccellini

The

Wea

ther

Channe

l & NWS/

NCEP


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Measure potential for

DESTRUCTION to property

and loss of life from

tornadoes and hurricanes

Fujita and Saffir-Simpson Scales


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Measurespotential forhumanandeconomic

DISRUPTION

Categories(1thru5)

NESIS


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SNOWFALL

WINDSPEED

TEMPERATURE

DURATION

SNOWFALL RATES STORM INTENSITY

GROUND TEMPERATURES

SNOWSTORM IMPACTDUE TO:


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A measure that is based on the integratedeffects of storm snowfall in the NortheastUnited States

What NESISis

Based on areal coverage of snowfall

amounts and population affected


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LOOKED AT 30 CASES

1950-2000

CONTOUREDSNOWFALL

at 4, 10and at

20 intervals

THOSE CONTOURS

REPRESENT:

(1) anAREA(2) anAFFECTED POPULATION

Feb 1978

Mar1993


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Mostly 4-10, small 10+

NESIS VALUES

Close to1


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Small 4, Largerareaof10+, small 20+

NESISVALUES

Closeto3


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Evenlargerareaof4+, 10+, 20+

NESIS VALUES

Greaterthan8


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NESISCATEGORIES

CATEGORY NESISVALUES # 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 EXT REME

Being tested at NCDC for possible

NWS operational use


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Climate Factors Influencing Winter Storms

1. El Nio/ La Nia cycle

2. North Atlantic Oscillation


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El Nio and La Nia


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SST(C) and Departures

28oC is approximate threshold for deep tropical convection

28 28


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ENSO Tropical Rainfall

El Nio: Tropical convection, jet stream extended eastward

La Nia: Tropical convection, jet stream retracted westward

EL Nio

Enhanced

Convection

La Nia

suppressedconvection


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El Nio:

Extended Jet Stream

More zonal flow over U.S.

South shift of storm track

Weaker Hudson Bay Low

Fewer arctic outbreaks

La Nia:

Retracted Jet Stream

More meridional flow

Blocking over N. Pac

Stronger Hudson Bay Low

More arctic outbreaks


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North Atlantic Oscillation (NAO)


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NAO Air Pressure and Winds

at 30,000 ft

1980s- 2001 1950s-1960s

++-

-

NAO affects the Atlantic jet stream/ storm trackNAO affects the Atlantic jet stream/ storm track

Tremendous differences in poleward heatTremendous differences in poleward heat

transporttransport and temperatures at high latitudesand temperatures at high latitudes


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Positive (warm) Phase of Wintertime NAO

Temperature Precipitation

Warmer Colder Wetter Drier


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NAO: DJF Time Series

50

55

60

6570 7

580 8

5

90

9500

Positive: 1980s-present

Weaker Hudson Bay Low

Arctic air confined to Canada

Milder Temperatures

Negative: 1950s-1960s

Stronger Hudson Bay Low

More Arctic outbreaks

Cooler Temperatures


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Moderate-to-Strong

El Nios

Negative NAO:

Cooler in SE,

Mid-Atlantic, NE

Positive NAO:

Warmer in SE,

Mid-Atlantic, NE

El Nio NAO

Temperature Composites


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Daily NAO Index


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Winter Weather (Paul Kocin)