1. A Climatology of Flash Flood Events in the NWS Eastern Region Alan M. Cope National Weather Service Mount Holly, New Jersey Alan.Cope@noaa.gov

2. Part 1: All FF Events Spatial and Temporal Distribution of Flash Flood Events

3. Methodology Do a climatological study of flash flood events only, not warnings or verification. Download data for all flash flood events in NWS Eastern Region, 1996-2005, from the Verification/Storm Data “Stats on Demand” web site. Stratify data by year, time of year, time of day, sub-region, WFO, etc. Plot the results…

7. Flash Flood Events by CWA, 1996-2005

9. Flash Flood Events by County, 1996-2005

13. Ohio ValleyNew England SouthMid Atlantic

17. Part 1 Conclusions Total number of FF Events in NWS-ER varies, from year to year, by a factor of 3 to 4. FF Definition change in 2001 significantly reduced the number of cool season FF Events. Total number of FF Events varies by a factor of 10 or more from one CWA to another in ER. A large majority of FF events occur during the warm season (May through September). Most FF events occur from 1900 to 0300 UTC, especially during the three summer months. In the Ohio Valley, FF events peak in June; in the South, the peak is in August-September.

18. Part 2: Summer FF Events Composite Charts: Means and Anomalies

19. Methodology Looked at FF events in summer months (Jun, Jul, Aug). Looked for "significant" days with >= 10 FF events in each sub-region (>=8 in South and New England). Removed days with a named/organized tropical system anywhere in ER. For multi-day events (<=3 days apart), used only the one day with most FF events. Also noted start time (1 st FF event) to nearest 3 hours. Some days were "significant" in more than one sub-region. Created composites from NCEP/NCAR global re-analysis and NARR data sets, via NOAA/ESRL web sites.

20. Ohio Valley (20 Cases) 1996 06 18 18Z 1996 06 24 12Z 1996 07 19 06Z # 1996 08 08 18Z 1997 06 02 15Z 1997 06 18 12Z # 1998 06 11 15Z 1998 06 27 06Z 1998 08 25 15Z 2000 08 06 12Z 2001 06 06 12Z 2001 07 08 09Z 2001 07 18 06Z 2001 08 12 15Z 2003 06 14 21Z 2003 07 08 06Z 2003 07 21 15Z 2003 07 27 21Z 2003 08 27 12Z 2004 06 15 18Z New England (17 Cases) 1996 06 13 18Z 1996 07 03 21Z 1996 07 31 15Z 1997 07 15 06Z 1998 06 13 15Z $ 1998 06 19 21Z 1998 06 30 18Z 1998 08 17 15Z 1999 08 26 09Z $ 2000 07 16 00Z 2000 08 11 18Z 2003 08 04 18Z 2003 08 11 15Z 2004 06 17 21Z 2005 06 16 18Z 2005 06 29 15Z 2005 07 18 18Z South (18 Cases) 1996 06 09 15 1996 08 12 15 1997 06 01 18 1999 06 29 15 2000 07 24 09 2000 08 04 15 2001 06 25 09 2001 07 29 15 2002 08 28 06 2003 06 08 21 2003 06 16 15 2003 07 06 18 2003 07 13 21 2003 07 29 18 2003 08 05 09 @ 2003 08 16 12 2005 07 07 09 2005 08 09 18 Mid Atlantic (19 Cases) 1996 07 19 09Z # 1996 08 08 15Z 1997 06 18 18Z # 1998 06 13 15Z $ 1998 06 23 21Z 1998 07 08 15Z 1999 08 20 15Z 1999 08 26 21Z $ 2000 07 14 21Z 2000 07 31 18Z 2000 08 12 15Z 2001 06 22 18Z 2001 08 11 15Z 2003 06 12 21Z 2003 07 22 21Z 2003 08 05 18Z @ 2004 07 12 12Z 2004 07 27 21Z 2004 08 12 21Z Flash Flood “Big Day” Cases

22. Ohio Valley New England SouthMid Atlantic NWS-ER “Sub-Regions”

23. Ohio Valley New England SouthMid Atlantic MSLP Composite Mean

24. Ohio ValleyNew England SouthMid Atlantic MSLP Composite Anomaly

25. Ohio ValleyNew England SouthMid Atlantic 500mb Height Composite Mean

26. Ohio ValleyNew England SouthMid Atlantic 500mb Height Composite Anomaly

27. Ohio ValleyNew England SouthMid Atlantic 700mb Specific Humidity Mean

28. Ohio Valley New England SouthMid Atlantic 700 mb SH Composite Anomaly

29. Ohio ValleyNew England SouthMid Atlantic 925mb V-Wind Composite Mean

30. Ohio ValleyNew England SouthMid Atlantic 925mb V-Wind Composite Anomaly

31. Ohio ValleyNew England SouthMid Atlantic 250mb U-Wind Composite Mean

32. Ohio ValleyNew England SouthMid Atlantic 250mb U-Wind Composite Anomaly

33. Ohio ValleyNew England SouthMid Atlantic 250mb Total Wind Composite Mean

34. Part 2 Conclusions Composite analyses show different signals for each NWS-ER “Sub-region”. Ohio valley sub-region seems most different, likely due to being west of the Appalachian Mtns. Negative height anomalies are found to the west of each sub-region, except Ohio Valley. Positive moisture anomalies are found over each sub- region. Positive v-wind anomalies are found over or near each sub-region. Upper-level jet streak pattern indicates favorable position for large-scale upward motion.

35. THE END Expanded version of Part 2 is at ftp.werh.noaa.govftp.werh.noaa.gov /share/PHI/FF_NWS-ER_Study.ppt