Case Studies of Warm Season Cutoff Cyclone Precipitation Distribution

1. Case Studies of Warm Season Cutoff Cyclone Precipitation Distribution Jessica Najuch Department of Earth and Atmospheric Sciences University at Albany, State University of New York Advisors: Lance Bosart and Dan Keyser NWS Focal Points: Tom Wasula and Ken LaPenta

2. Outline of Presentation • Explain the motivation and focus behind my research • Look at my progress to date • Climatology of monthly precipitation distribution • Climatology of monthly tracks • Examine two case studies • Discuss preliminary results and future work

3. Motivation • Cutoff cyclones have diverse precipitation patterns • Flash floods are a consistent forecasting problem • National 30-year average for flash flood deaths is 127 • Continuation of Matt Novak’s thesis but focus on the Northeast

4. Arcade, NY June 26, 1998

5. Focus • Stratify precipitation distribution relative to cutoff cyclone tracks as identified in composites developed by Matt Novak (2003). • Map/understand cutoff cyclone precipitation characteristics in composites especially in relation to terrain. • Document mesoscale precipitation signatures in case studies representative of each of the composites.

6. Warm Season Composite Mean Cutoff Cyclone Tracks M. Novak (2003)

7. Focus Continued • Understand role of terrain/low-level jet interactions in determining the precipitation distribution in case studies representative of each of the composites. • Use composites to look for changes in orientation of the cutoff in each case. • Assess precipitation signatures in terms of shear/CAPE profiles in selected case studies.

8. Progress to Date • Created a climatology of monthly precipitation distribution • Hand drew the tracks of all 500 hPa closed lows from 1980-1998 • Graphical and textural record of tracks • Created and studied many composites for two of four case studies

9. Climatology Of Monthly Precipitation Distribution • NCEP Unified Precipitation Dataset (UPD) • 50 year dataset • Each day a cutoff with precipitation passed through a specified domain • Months June through September

10. Outer Domain

11. inches/day mm/day

12. inches/day mm/day

13. inches/day mm/day

14. inches/day mm/day

15. inches/day mm/day

16. Climatology of Monthly Tracks • Used NCEP/NCAR reanalysis dataset • Plotted 500 hPa geopotential height at 30m intervals • Tracked, by hand, cutoff cyclones at 6 hour intervals 1980-1998 • Cyclone was considered cutoff where a height minimum was surrounded by at least one closed contour

18. Cases 1. 6/30/98-7/1/98 -Great Lakes Category of a Closed Low 2. 7/3/96-7/5/96 -Hudson Bay Category of a Closed Low 3. 7/18/96-7/19/96 -Great Lakes Category of a Closed Low 4. 7/29/96-8/2/96 -Great Lakes Category of a Closed Low

19. Case: 6/30/98 – 7/1/98 • Great Lakes Category of a closed low • Produced all types of significant weather, many tornadoes • OH, WV, 6-10” of rain • VT, NY flash floods

20. Tornadoes: 17 Hail: 64 Wind: 283

21. Maximum Precipitation: Woonsocket, RI 3.58 inches 2-day precipitation plot (in) ending 12Z 1 July 1998

22. 980630/1200F000 MSLP (hPa) and 1000-500 Thickness (dam) 500 Hght (dam) and Abs. Vorticity (x10-5 s-1) 250 Hght (dam) and Isotachs (m s-1) 850 Hght (m) and Isotachs (m s-1)

27. 980701/1200F000 MSLP (hPa) and 1000-500 Thickness (dam) 500 Hght (dam) and Abs. Vorticity (x10-5 s-1) 250 Hght (dam) and Isotachs (m s-1) 850 Hght (m) and Isotachs (m s-1)

31. Case: 7/3/96 – 7/5/96 • Hudson Bay Category of a closed low • Flash flood producer • Widespread heavy precipitation in eastern NY, stretching northeastward into Maine

32. Maximum Precipitation: Malone, NY 3.63 inches

33. 960703/1200F000 MSLP (hPa) and 1000-500 Thickness (dam) 500 Hght (dam) and Abs. Vorticity (x10-5 s-1) 250 Hght (dam) and Isotachs (m s-1) 850 Hght (m) and Isotachs (m s-1)

35. 960704/1200F000 MSLP (hPa) and 1000-500 Thickness (dam) 500 Hght (dam) and Abs. Vorticity (x10-5 s-1) 250 Hght (dam) and Isotachs (m s-1) 850 Hght (m) and Isotachs (m s-1)

37. 960705/1200F000 MSLP (hPa) and 1000-500 Thickness (dam) 500 Hght (dam) and Abs. Vorticity (x10-5 s-1) 250 Hght (dam) and Isotachs (m s-1) 850 Hght (m) and Isotachs (m s-1)

39. Preliminary Results • There is a general eastward shift of heavy precipitation due to cutoff cyclones from June to September • Entrance/exit regions of low-level jets assoc. with cutoff cyclones can strongly enhance heavy precipitation • Heavy precipitation normally falls either to the right or left of track, not on track • Cyclonic vorticity advection has much influence on enhancing heavy precipitation

40. Future Work • Continue producing the UPD climatology plots for specific tracks and compare to monthly composites • Analyze precipitation patterns between cutoffs of the same track • Further analyze composites to see how speed and direction of movement of lows affect precipitation distributions

41. Future Work Cont. • Obtain radar data to map/understand how precipitation is associated with the composites for each case study • Determine what percentage of monthly precipitation is due to cutoff cyclones versus any other synoptic or mesoscale feature • Build a user friendly database of cutoffs from 1980-1998 • Put all of this research into one nice thesis!