Rating Snowstorms Based on Travel ImpactsRating Snowstorms Based on Travel Impacts

Ernie OstunoErnie Ostuno

National Weather Service, GRRNational Weather Service, GRR

Storm Impact: Travel Storm Impact: Travel ConditionsConditions

Recent survey found (not surprisingly) that travel impacts were the leading cause of people altering their normal routines during snowstorms

Two Methods of Ranking Two Methods of Ranking StormsStorms• Pre-Storm:Pre-Storm:

– Saffir/Simpson scale: damage potential

• Post-Storm:Post-Storm:– EF scale: damage assessmentEF scale: damage assessment

Winter Storms: Criteria vs. Winter Storms: Criteria vs. ImpactImpact

• NWS warning criteria based on NWS warning criteria based on amountamount and and raterate of snow of snow

• Impact: primarily the effect on travel Impact: primarily the effect on travel conditions, which we don’t explicitly conditions, which we don’t explicitly forecast forecast

• Zielinski (2002), Grumm and Hart (2001) Zielinski (2002), Grumm and Hart (2001) rated winter storms rated winter storms based on meteorologybased on meteorology

• Kocin and Ucellini (2004) rated winter Kocin and Ucellini (2004) rated winter storms storms based on impactsbased on impacts

• The impacts did not include taking into The impacts did not include taking into account some important variablesaccount some important variables

Northeast Storms Severity Northeast Storms Severity IndexIndex• Based on amount of snow that affects the Based on amount of snow that affects the

greatest area/most populationgreatest area/most population• Somewhat analogous to the EF-scale; tornado Somewhat analogous to the EF-scale; tornado

will likely get a higher rating if it hits a citywill likely get a higher rating if it hits a city• Ranks 11-12 Feb 1983 higher than 6-7 Feb Ranks 11-12 Feb 1983 higher than 6-7 Feb

19781978• Not accounted for: Timing, winds, Not accounted for: Timing, winds,

temperatures, local severitytemperatures, local severity

Variables Affecting Travel Variables Affecting Travel ImpactsImpacts• Snow: Amount, Rate, TimingSnow: Amount, Rate, Timing• Wind: Speed and Duration Wind: Speed and Duration • Temperature: Hypothermia, Road SaltTemperature: Hypothermia, Road Salt• Icing: Freezing rain, rain to snowIcing: Freezing rain, rain to snow

Ranking Historic Northeast Ranking Historic Northeast SnowstormsSnowstorms• February 6-7, 1978February 6-7, 1978

• January 7-8, 1996January 7-8, 1996

• February 11-12, 1983 and 2006February 11-12, 1983 and 2006

• February 16-17, 2003February 16-17, 2003

• April 1, 1997 and April 6, 1982April 1, 1997 and April 6, 1982Ranking Factors: Amount of snow, winds, persistence of deep snow

Societal impacts to account for: Economic disruption, travel bans

Discussion point: which is more important, snow amount or wind?

Drifting snow and snowfall rates are important factors in affecting travel, as well as timing

What makes a storm memorable enough to mark anniversaries of it?

Rankings by Snow, Wind*Rankings by Snow, Wind*

SnowSnow

17.7…2006 17.7…2006

15.5…198315.5…1983

15.4…199615.4…1996

15.1…197815.1…1978

13.1…200313.1…2003

*Average of BDR and BDL snow totals and peak winds

** Top ranking for each category is given 5 points, next highest given 4 points, etc., then added together. Wind is given a weighting factor of 1.5

WindWind

40…197840…1978

37…199637…1996

36…200636…2006

33…200333…2003

28…198328…1983

Rank Rank points** points**

2006…9.52006…9.5

1978…9.51978…9.5

1996…91996…9

1983…5.51983…5.5

2003…42003…4

0

5

10

15

20

25

30

35

40

1 2 3 4 5 6 7 8 9 10 11 12

1978

1983

1996

2003

A Look at One Possibly Important Variable: Snow Depth Following some of the Big Storms

Snow depth in inches (y-axis) measured each day after the storm (x-axis)

Post-storm assessment ranking:

10 inches or more on the ground 5 days after = 1 point

10 inches or more on the ground 10 days after = 2 points

Final RankingFinal Ranking

Rank points Rank points

1978…11.51978…11.5

1996…111996…11

2006…10.52006…10.5

1983…6.51983…6.5

2003…42003…4

““The Old 1 to 5 Scale”The Old 1 to 5 Scale”

Wind (mph)Wind (mph)Snow (In)Snow (In) Temp (F) Temp (F)

>40… 5>40… 5 >12… 5>12… 5 <15… 5<15… 5

30-40… 430-40… 4 8-12… 4 8-12… 415-20… 415-20… 4

20-29… 320-29… 3 4-8… 3 4-8… 320-25… 320-25… 3

10-19… 2 2-4… 210-19… 2 2-4… 225-30… 225-30… 2

<10… 1<10… 1 <2… 1<2… 1 >30… 1>30… 1

*Amounts can vary based on forecast zones*

Graphical Forecasts Graphical Forecasts Peak WindPeak Wind + Snow + Snow +Temp +Temp

= Impact = Impact

Impact Forecast generated from graphics that are already being produced and calculated as follows:45 % Wind + 40 % Snow + 15 % Temperature

Example: Wind = 35, Snow = 10 and Temp = 20

Impact = 4(.45) + 4 (.4) + 3 (.15) = 3.85

Let’s Look at Some Let’s Look at Some ExamplesExamples

Discussion Discussion points points • Severity vs. ImpactSeverity vs. Impact

• Timing is everything? Timing is everything? • Can we forecast road conditions?Can we forecast road conditions?• What about icing?What about icing?

Two recent cases show the difficulties in assessing Two recent cases show the difficulties in assessing impactsimpacts

Winter Storm of 3 Feb Winter Storm of 3 Feb 20072007

• High impact event with road closures, High impact event with road closures, blizzard conditions and extreme coldblizzard conditions and extreme cold

• Impact mitigated since it hit on Impact mitigated since it hit on weekendweekend

• Highly variable conditions, but frequent Highly variable conditions, but frequent whiteouts in falling and blowing snowwhiteouts in falling and blowing snow

Lake Effect Blizzard with Whiteouts, Low Wind Chills

Winter Storm of 30 Jan Winter Storm of 30 Jan 20082008

• High Impact rain to snow event with High Impact rain to snow event with extremely poor travel conditionsextremely poor travel conditions

• Quick temperature drop with a “flash Quick temperature drop with a “flash freeze” of rain into a sheet of snow freeze” of rain into a sheet of snow covered icecovered ice

• Cold temperatures greatly reduced the Cold temperatures greatly reduced the effectiveness of road salteffectiveness of road salt

• Travel conditions were bad for several Travel conditions were bad for several daysdays

Not a lot of snow, but worst driving conditions EVER

Other high impact winter Other high impact winter events:events:• Black iceBlack ice• ““Clear Air” drifting of snowClear Air” drifting of snow• Localized whiteoutsLocalized whiteouts• Localized dense fog from snowmelt Localized dense fog from snowmelt • Dirt Roads icing over in thaw situationsDirt Roads icing over in thaw situations• High winds after ice storms causing High winds after ice storms causing

continued power outagescontinued power outages

These are high impact events that we must anticipate and communicate better!

Strategy for Communicating Strategy for Communicating Impacts of Winter StormsImpacts of Winter Storms

• A rating system for winter storms based on A rating system for winter storms based on impacts can help communicate how “bad” a impacts can help communicate how “bad” a storm will bestorm will be

• Existing forecast parameters can be used to Existing forecast parameters can be used to calculate impactscalculate impacts

• No easy way to account for so many variablesNo easy way to account for so many variables• Each storm is different; recognize the main Each storm is different; recognize the main

impactsimpacts• Stress major impacts in briefings/NWSChat/AFDsStress major impacts in briefings/NWSChat/AFDs• Choose wording that best conveys what the Choose wording that best conveys what the

major impacts will be major impacts will be

In SummaryIn Summary

Diagnose the Meteorology

Assess the Impacts

Describe the Event