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Climatology and Environments of Derecho-Producing Convective Systems

Climatology and Environments of Derecho-Producing Convective Systems. Mike Coniglio CIMMS/OU BAMEX Forecasters Workshop March 18-19, 2003. Outline. Derecho definitions & climatology of 15 May - 15 July events 500-mb flow patterns Parameter distributions

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Climatology and Environments of Derecho-Producing Convective Systems

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  1. Climatology and Environments of Derecho-Producing Convective Systems Mike Coniglio CIMMS/OU BAMEX Forecasters Workshop March 18-19, 2003

  2. Outline • Derecho definitions & climatology of 15 May - 15 July events • 500-mb flow patterns • Parameter distributions • wind speeds derived from NCEP/NCAR Reanalysis • proximity soundings

  3. “Mid-End” Derechos (Johns and Hirt, 1987) • progressive or swaths of wind gusts  26 ms-1 with a major axis length  400 km. •  3 reports, separated by 64 km or more, of either F1 damage, or gusts  33 ms-1 • no more than 3 h can elapse between successive wind gust reports. • multiple swaths of wind gusts must be a part of the same MCS and show linear/bowed radar signature

  4. “Low-End” Derechos • progressive or swaths of wind gusts  26 ms-1 with a major axis length  400 km. •  3 reports, separated by 64 km or more, of either F1 damage, or gusts  33 ms-1 • no more than 3 h can elapse between successive wind gust reports. • multiple swaths of wind gusts must be a part of the same MCS and show linear/bowed radar signature

  5. “High-End” Derechos • progressive or swaths of wind gusts  26 ms-1 with a major axis length  400 km. •  3 reports, separated by 64 km or more, of either F1 damage, or gusts  33 ms-1 • no more than 3 h can elapse between successive wind gust reports. • multiple swaths of wind gusts must be a part of the same MCS and show linear/bowed radar signature •  3 reports of F2 damage or gusts  40 ms-1 during the initial and mature stages

  6. Distribution of all Derechos (131)

  7. Distribution “Low-End” Derechos (46)

  8. Distribution of “Mid-End” Derechos (54)

  9. Distribution of “High-End” Derechos (31)

  10. Temporal Distribution of all Derechos within BAMEX (99)

  11. Patterns associated with Derechos (Johns, 1993) “Dynamic” Pattern “Warm Season” Pattern

  12. Variability of 500-mb patterns among BAMEX events (99) • Dominant synoptic-scale influence: • Ridge (39%) • Upstream trough (35%) • Broad, long-wave trough (16%) • Upstream trough/ridge couplet (12%) • Upstream trough/zonal flow (8%) • Zonal (13%) • Others (13%)

  13. Ridge example:

  14. Broad, Upstream Trough example:

  15. Upstream Trough/Ridge Couplet example:

  16. Upstream Trough/Zonal Flow example:

  17. Zonal Flow example:

  18. Other example:

  19. 925-mb Wind Speeds Derived from Large-Scale Analyses (99):

  20. 500-mb Wind Speeds Derived from Large-Scale Analyses (99):

  21. 200-mb Wind Speeds Derived from Large-Scale Analyses (99):

  22. CAPE/0-2.5 km shear Derived from Proximity Soundings (38):

  23. CAPE/0-5 km shear Derived from Proximity Soundings (38):

  24. CAPE/5-10 km shear Derived from Proximity Soundings (38):

  25. Vertical RH Distribution Derived from Proximity Soundings (38):

  26. Vertical e Distribution Derived from Proximity Soundings (38):

  27. Summary • Climatological distributions • “Low-End” events favored in southern & eastern portions of BAMEX domain • “High-end” events favored in northern corridor • Temporally, peak in midpoints spread between 2000-0800 UTC • 500-mb large-scale patterns • Upstream trough occurs with nearly equal frequency to “classic” warm-season derecho pattern • Remaining events (26%) occur under zonal flow and mixture of the three regimes

  28. Summary (cont.) • Parameter distributions • 500 and 200-mb wind speeds (derived from NCEP/NCAR Reanalysis) are significantly larger for “high-end” events • 0-2.5 km shear is mostly weak to moderate; 0-5 km usually shear moderate to strong • Shear above 5 km is usually non-zero  mid-upper-level environment is usually baroclinic • 3-4 km AGL is often relatively dry • Vertical decrease in e relatively large  large convective instability

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