Patterns of Historic River Flood Events in the Mid-Atlantic Region - PowerPoint Presentation

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Patterns of Historic River Flood Events in the Mid-Atlantic Region

Richard H. GrummNOAA/NWS Weather Forecast Office, State College, Pennsylvaniaand Charles ChillagNOAA/NWS Middle Atlantic River Forecast Center, State College, PennsylvaniaContributions byAlaina MacFarlane and Ron Holmes

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Motivation

Ability to compare and rank flood events

For impacts and Federal disasters

Learning from the past

to gain knowledge

Understand flood events

Patterns and conditions for flooding

Education

 forecasters, users, students

Knowledge and data should be F U N

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Methods and Data

Mid-Atlantic River Forecast Center Flood data

From archive (points/stages) and research

Extensive dataset with pre-20

th

Century examples

Based on points over flood and ranked

Climate data

 rainfall observations

Where how much when.

Re-analysis data

Reconstruct the cases 20

th

Century, NCEP/NCAR, CFSR

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20th Century Re-analysis

Used for cases prior to 194924 pressure levels including 10 hPa6-hourly datanetCDF or plot-4-U

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20th Century Re-analysis site

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MARFC Flood Power RankingsIs a arbitrary value weighted according to flood severity

Simple Method to rate flood based onNumber of points  raw number biasPower Ranking based on severity/Type of Flood:minor (1) – moderate(5) – major (10)– unknown (1)

Points

Minor

Moderate

Major

Unknown

Ranking

Event

17

5

5

5

2

82

Example

140

34

47

58

1

850

Jan

19

96

120

20

19

81

0

925

Agnes 1972

109

34

43

32

0

569

Lee

32

10

11

11

0

175

May 1946

17

2

7

8

0

117

May 1924

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Flood Data Display and Access main access site

Extensive database with pre-20th Century casesTop floods of all time and MonthSortable by number, categories, and rankingsEvent summaries

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Top 20Flood EventsRanked by points over flood stage

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January

record by EventsandthenPower ranking

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May Rankings1946 event is shown later

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June Events

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September Events

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Case Example

Flooding Event of 26 May 1946

20

th

Century Re-analysis Example

Wet month with several day wet period

Sunbury, PA wet May

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May 1946provides summary of event type and flood data

Flood Statistics

Year Count

Month Count

 

 

Total

Minor

Moderate

Major

Missing

Power Ranking

4 of 8

2 of 2

 

 

32

10

11

11

0

175

Weather Summary

See May 21, 1946 flood. The ridge retrograded about 24 May and a surge of high PW air came up the coast. It was a textbook case with a quasi east-west boundary and easterly flow setting up over the Mid-Atlantic region with a deep southerly jet into it. Heavy rainfall was with strong easterly flow along the boundary and a surge of high PW up the coast. The low was a southern stream low. Similar to the pattern for the March 2010 Boston/RI flood event in many respects. Probably a Frontal to synoptic transition. – (Rich Grumm National Weather Service State College, PA)

Additional Information

MARFC Power Ranking is (Minor = 1 - Moderate = 5 - Major = 10 - Missing = 1)

NOAA Daily Weather Maps Link

NOAA Northeast Regional Climate Center Link

 

 

 

 

 

 

 

 

 

 

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NAMETYPETotal Precipitation SUNBURYCOOP11.80SELINSGROVE 2 SCOOP11.32LANSFORDCOOP11.15TAMAQUA 4 N DAMCOOP10.96WATROUS 9 S LEE FIRECOOP10.88QUAKERTOWNCOOP10.64LANSFORD FOREMANS SHCOOP10.58TAMAQUACOOP10.53JIM THORPECOOP10.29MONROETON 2 SCOOP10.23TOWER CITY 5 SWCOOP10.19FREELANDCOOP10.19SUNBURY APWBAN10.14BERWICKCOOP10.11GREENWOOD RSVRCOOP10.09GRANTVILLE 2 SWCOOP10.04NEW CASTLE 1 NCOOP9.96RETREAT 1 SWCOOP9.90KANE 1 NNECOOP9.89ALBIONCOOP9.88RENOVOCOOP9.82GOULDSBOROCOOP9.70PLEASANT MT 1 WCOOP9.61LEHIGHTONCOOP9.60CANTON 1 NWCOOP9.59NEW BLOOMFIELDCOOP9.52WILKES BARRECOOP9.51BEAR GAPCOOP9.50EAGLES MERECOOP9.46Williamsport AreaThreadEx9.45WILLIAMSPORTWBAN9.45NEWBURG 3 WCOOP9.45

May 1946

Rainfall

For

Month

over

Pennsylvania

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Sunbury Rainfall May 1946

A wet periodWettest May at SunburySeveral days of rainfallAntecedent conditions played a role. Some flooding 21 May in NY 1 point!

Date

Rainfall

1946-05-01

0.00

1946-05-02

0.00

1946-05-03

0.00

1946-05-04

T

1946-05-05

0.09

1946-05-06

0.00

1946-05-07

0.02

1946-05-08

0.66

1946-05-09

0.00

1946-05-10

0.00

1946-05-11

0.02

1946-05-12

0.16

1946-05-13

0.92

1946-05-14

0.00

1946-05-15

0.67

1946-05-16

0.00

1946-05-17

0.23

1946-05-18

0.34

1946-05-19

0.45

1946-05-20

0.00

1946-05-21

1.54

1946-05-22

0.29

1946-05-23

0.00

1946-05-24

0.00

1946-05-25

0.00

1946-05-26

1.44

1946-05-27

1.53

1946-05-28

3.22

1946-05-29

0.22

1946-05-30

0.00

1946-05-31

0.00

Sum

11.80

Average

-

Normal

3.72

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The Pattern for the Event

20

th

Century re-analysis data

250 hPa heights and anomalies

 sharp wave

500 hPa heights and anomalies cut-off

High PW East-west then more north-south

LLJ

Easterly flow north of frontal boundary

Southerly flow in warm sector (+5

s

)

Textbook P A T

T

E R N

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End of May Pattern

Large ridge 20-26 May over northwestern Atlantic

The East Coast and Mid-Atlantic had wet period

Some location had wettest May on record

Sunbury showed wet period

Persistent pattern then big rain

 Flood

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Event Types Emerge

Strong south-north PW surges

With strong LLJ

Maddox Synoptic Pattern

Ridge to EAST often critical

Strong Frontal Systems with easterly flow

Tropical Systems

With Maddox-Frontal often record events

Lesser seen cut-off low events

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Cut-off Events

Lack the high PW air

Slow moving

Cold core

Instability driven? There are fewer of these and typically not many points and low power rankings.

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Patterns with CFSR Cases

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Key Issues and follow-ons

Data base exists to rank and sort floods

Not all the floods have been characterized

The data exist to accomplish this back into the 19

th

Century

Good learning and teaching tool

Good basic student research Project

Could be semi-automated?

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Summary

Ability to compare and rank flood events

For impacts and Federal disasters

Learning from the past

to gain knowledge

Power rankings are helpful

Understand flood events

Patterns and conditions for flooding

Education

 forecasters, users, students

Use our knowledge to improve pattern recognition and perhaps better identify

Extreme Weather Events

(EWE)