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Case Studies of Warm Season Cutoff Cyclone Precipitation Distribution

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. Introduction.

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Case Studies of Warm Season Cutoff Cyclone Precipitation Distribution

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  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. Introduction • Forecasting heavy precipitation associated with warm season cutoff cyclones can be very challenging • These challenges arise from physiographic features and from rapid changes in cutoff cyclone structure • These forecasting problems are particularly difficult in the northeastern US

  3. Motivation • Given these forecasting problems, there needs to be more understanding of the diverse precipitation patterns associated with cutoff cyclones • These precipitation patterns lead to many unforecasted flash floods • Continue previous warm season cutoff cyclone research done by Matt Novak (CSTAR)

  4. Literature Review • Hawes, J. T. and S. J. Colucci, 1986: An Examination of 500 mb Cyclones and Anticyclones in National Meteorological Center Predication Models • G. D. Bell, and L. F. Bosart, 1989: Climatology of Northern Hemisphere 500 mb Closed Cyclone and Anticyclone Centers • M. J. Novak, 2002: Warm Season 500 hPa Closed Lows • B. A. Smith, 2003: Cutoff Cyclones: A Global and Regional Climatology and Two Case Studies

  5. Focus • Stratify precipitation distribution relative to cutoff cyclone tracks as identified in composites developed by Matt Novak (2002) • 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 (2002)

  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. Climatology of Monthly Precipitation Distribution • NCEP Unified Precipitation Dataset (UPD) • 51 year dataset, daily observations from 12Z–12Z • Each day a cutoff with precipitation passed through 34°-48°N and 60°-92°W • June through September (1948-1998) • Calculated daily precipitation and percentage of climatological precipitation

  9. Outer Domain

  10. inches/day mm/day

  11. inches/day mm/day

  12. inches/day mm/day

  13. inches/day mm/day

  14. inches/day mm/day

  15. % of Climo

  16. % of Climo

  17. % of Climo

  18. % of Climo

  19. % of Climo

  20. Climatology of Monthly Tracks • Used NCEP/NCAR reanalysis dataset • Plotted 500 hPa geopotential heights at 30 m intervals • Tracked cutoff cyclones through a subjective hand analysis at 6 hour intervals (1980-1998) • A cutoff cyclone was defined by one closed 500 hPa isoheight for at least 24 hours

  21. Results of the Climatology • There is a general eastward shift of heavy precipitation due to cutoff cyclones from June to September • The most intense daily rainfall associated cutoff cyclones occurs in the month of August • The highest percentage of precipitation due to warm season 500 hPa cutoff cyclones occurs in the month of June and the lowest in the month of August • Daily precipitation associated with cutoff cyclones is most widespread along the Atlantic Coast

  22. 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

  23. 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

  24. Key Players of this Case • Region 1: Severe weather reports due to Midwest nocturnal convection between 00Z and 09Z on 30 June 1998 • Region 2: Severe weather reports associated with a pre-frontal trough and warm sector between 06Z on 30 June 1998 and 14Z on 01 July 1998 • Huge swath of heavy precipitation fell over NY/PA border extending to Cape Cod • Jet-dynamics well in place but no strong baroclinic zone present • 500 hPa trough pivots from positive tilt to a slightly negative tilt

  25. Maximum Precipitation: Woonsocket, RI 3.58 inches/~91 mm 2-day precipitation (in) ending 12Z 1 July 1998

  26. 980630/0000F00 1000 Hght (m) and 1000-500 Thickness (dam) 850 Hght (m) and Isotachs (m s-1) 250 Hght (dam) and Isotachs (m s-1) 500 Hght (dam) and Abs. Vorticity (x10-5 s-1)

  27. 980630/1200F00 1000 Hght (m) and 1000-500 Thickness (dam) 850 Hght (m) and Isotachs (m s-1) 200 Hght (dam) and Isotachs (m s-1) 500 Hght (dam) and Abs. Vorticity (x10-5 s-1)

  28. 980701/0000F00 1000 Hght (m) and 1000-500 Thickness (dam) 850 Hght (m) and Isotachs (m s-1) 200 Hght (dam) and Isotachs (m s-1) 500 Hght (dam) and Abs. Vorticity (x10-5 s-1)

  29. Radar Composite LVL: 1 0800 UTC 30 June 1998 National Composite LVL:1 30-Jun-98 08:00:00 V2 L V1 L – Surface Low V – 500 hPa Vort Max

  30. Radar Composite LVL: 1 1300 UTC 30 June 1998 V3 V2 L V1 L – Surface Low V – 500 hPa Vort Max

  31. Radar Composite LVL: 1 1830 UTC 30 June 1998 National Composite LVL:1 30-Jun-98 18:30:00 V3 L V2 V1 L L – Surface Low V – 500 hPa Vort Max

  32. Radar Composite LVL: 1 2330 UTC 30 June 1998 National Composite LVL:1 30-Jun-98 23:30:00 V3 L V1 L V2 L – Surface Low V – 500 hPa Vort Max

  33. V2 V1

  34. V3 V2 V1

  35. V3 V2 V1

  36. V3 V2

  37. Surface Pressure (hPa) Hand Analysis for 1200 UTC 30 June 1998

  38. ── Potential Temperature (C) ---- Mixing Ratio g/kg 1200 UTC 30 June 1998

  39. ── Potential Temperature (C) ---- Mixing Ratio g/kg 1800 UTC 30 June 1998

  40. http://weather.uwyo.edu

  41. http://weather.uwyo.edu

  42. Conclusions of First Case Study • Antecedent convective system over the OH/TN valley provides a moisture source for large swath of precipitation over NY/PA border • Corridor of heaviest precipitation along NY/PA border and east to southeast New England falls near 200 hPa jet-entrance region and associated 500 hPa vorticity maximum • Heavy rain is concentrated ahead of well defined surface trough but no strong baroclinic zone is present

  43. Conclusions of First Case Study Continued • There is dynamical forcing as evident by strong jets and strong 700 hPa ascent • Precipitation in northern NY and northern New England is likely driven by warm air advection as well as cyclonic vorticity advection beneath the 200 hPa jet • Convection in eastern PA, NJ, and southeast NY, late on the 30th, occurs beneath the 200 hPa jet in conjunction with a strong low-level jet

  44. What to Watch for When Dealing with 500 hPa Cutoff Cyclones…. • Refer to climatology to be aware of favored areas as well as amount of heavy precipitation • Pay attention to the location, speed, and track of cutoff cyclones using real time data • Watch for upper- and lower-level jet dynamics (exit/entrance regions) juxtaposed with vorticity maxima • Look for surface cyclone development creating low-level flows that draw in excess moisture

  45. 558 564 570 558 250 hPa ↓ jet 250 hPa ↓ jet 564 570 ↑ ← heavy rain V1 ← heavy rain 564 570 558 ↑ ← heavy rain 250 hPa jet → V2 V3 V1 V2 t t –Δt V3 V2 t + Δt

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