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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
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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 pastto 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-20th Century examples • Based on points over flood and ranked • Climate data rainfall observations • Where how much when. • Re-analysis data • Reconstruct the cases 20th Century, NCEP/NCAR, CFSR
20thCentury Re-analysis • Used for cases prior to 1949 • 24 pressure levels including 10 hPa • 6-hourly data • netCDF or plot-4-U
MARFC Flood Power RankingsIs 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)
Flood Data Display and Access main access site • Extensive database with pre-20th Century cases • Top floods of all time and Month • Sortable by number, categories, and rankings • Event summaries
Case Example • Flooding Event of 26 May 1946 • 20th Century Re-analysis Example • Wet month with several day wet period • Sunbury, PA wet May
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 • 20th 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 (+5s) • Textbook P A T T E R N
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
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.
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 19th 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 pastto 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)