Patterns of Historic River Flood Events in the Mid-Atlantic Region Richard H. Grumm NOAA/NWS Weather Forecast Office, State College, Pennsylvania and Charles Chillag NOAA/NWS Middle Atlantic River Forecast Center, State College, Pennsylvania Contributions by Alaina MacFarlane and Ron Holmes

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

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

20 th Century Re-analysisCentury Re-analysis Used for cases prior to pressure levels including 10 hPa 6-hourly data netCDF or plot-4-U

20 th Century Re-analysis site

MARFC Flood Power Rankings Is a arbitrary value weighted according to flood severity Simple Method to rate flood based on – Number of points  raw number bias Power Ranking based on severity/Type of Flood: – minor (1) – moderate(5) – major (10)– unknown (1) PointsMinorModerateMajorUnknownRankingEvent Example Jan Agnes Lee May May 1924

Flood Data Display and Access main access site main access site Extensive database with pre-20 th Century cases Top floods of all time and Month – Sortable by number, categories, and rankings Event summaries

Top 20 Flood Events Ranked by points over flood stage

January record by Events and then Power ranking

May Rankings 1946 event is shown later

June Events

September Events

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

May 1946 provides summary of event type and flood data Flood Statistics Year CountMonth Count TotalMinorModerateMajorMissing Power Ranking 4 of 82 of 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

NAMETYPETotal Precipitation SUNBURYCOOP11.80 SELINSGROVE 2 SCOOP11.32 LANSFORDCOOP11.15 TAMAQUA 4 N DAMCOOP10.96 WATROUS 9 S LEE FIRE COOP10.88 QUAKERTOWNCOOP10.64 LANSFORD FOREMANS SH COOP10.58 TAMAQUACOOP10.53 JIM THORPECOOP10.29 MONROETON 2 SCOOP10.23 TOWER CITY 5 SWCOOP10.19 FREELANDCOOP10.19 SUNBURY APWBAN10.14 BERWICKCOOP10.11 GREENWOOD RSVRCOOP10.09 GRANTVILLE 2 SWCOOP10.04 NEW CASTLE 1 NCOOP9.96 RETREAT 1 SWCOOP9.90 KANE 1 NNECOOP9.89 ALBIONCOOP9.88 RENOVOCOOP9.82 GOULDSBOROCOOP9.70 PLEASANT MT 1 WCOOP9.61 LEHIGHTONCOOP9.60 CANTON 1 NWCOOP9.59 NEW BLOOMFIELDCOOP9.52 WILKES BARRECOOP9.51 BEAR GAPCOOP9.50 EAGLES MERECOOP9.46 Williamsport AreaThreadEx9.45 WILLIAMSPORTWBAN9.45 NEWBURG 3 WCOOP9.45 May 1946 Rainfall For Month over Pennsylvania Rainfall

Sunbury Rainfall May 1946 A wet period Wettest May at Sunbury Several days of rainfall Antecedent conditions played a role. – Some flooding 21 May in NY 1 point!

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  ) Textbook P A T T E R N

End of May Pattern Large ridge 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

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

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.

Patterns with CFSR Cases

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?

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)