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Northwest Flow – Watch Out: Experience with a Dangerous Canadian Export

Northwest Flow – Watch Out: Experience with a Dangerous Canadian Export. David Zaff Science and Operations Officer Buffalo, NY Weather Forecast Office Oct 25, 2006. A Dangerous Canadian Export. Northwest Flow and Severe Weather.

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Northwest Flow – Watch Out: Experience with a Dangerous Canadian Export

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  1. Northwest Flow – Watch Out:Experience with a Dangerous Canadian Export David Zaff Science and Operations Officer Buffalo, NY Weather Forecast Office Oct 25, 2006

  2. A Dangerous Canadian Export

  3. Northwest Flow and Severe Weather • A classic severe weather outbreak over the Great Lakes region: • Warm frontal boundaries or within warm sector • High dewpoints • BUT some of the worst events have to due with upper air patterns, particularly with northwest flow aloft • Three-fourths of all Upper Ohio Valley events occur with northwest flow aloft Giordano et al. (1991) • Derechoes and MCSs often form under these flow patterns

  4. Northwest Flow and Severe Weather • Definition of Northwest flow: (Johns 1982) • Preceding event: • 500-mb long-wave ridge upwind of event • 500-mb long-wave trough downwind of event • 500-mb flow in event vicinity >280 degrees • Following event • Little change in 500-mb long wave pattern • 500-mb flow in event vicinity >260 degrees

  5. NCEP/NCAR Reanalysis 500mb Geopotential Height Composite Mean 1948-2006 Jul Aug Sep Apr May Jun

  6. Other Factors • Northwest flow aloft • July • Short-waves in the cold upper level trough • Boundaries!! • In particular…lake breeze fronts • Nearly 70% of tornadoes during VORTEX were associated with boundaries Markowski et al. (1998) • Nearly 95% of storms with 60+ dBZ reflectivies were associated with radar-observed convergence lines in a High Plains (CO) study Wilson and Schreiber (1986)

  7. Case studies • Northwest flow events: • (and local interactions with a lake breeze) • 30 July 1987 – F2 Cheektowaga Tornado • 30 June 2006 – F1 Cheektowaga Tornado • 23 July 2006 – Severe Weather • 28 July 2006 – Severe Weather

  8. 30 July 1987 • ~2130Z: F2 Tornado in Cheektowaga • (about 2 mi from the BUF airport) • No fatalities • millions of dollars damage

  9. 30 July 1987 • 500 mb Heights (Contoured) • 500 mb Temps (image) No Sounding for KBUF 12Z Upper Air Observations at 500 mb30 July 1987

  10. Southern Ontario Lake Ontario 30 July 1987 Lake Ontario Southern Ontario • At the surface • Niagara Falls: • KIAG 301800Z 19016KT 12SM BKNXXX 29/21 A2995 KIAG 301900Z 17011KT 4SM TSRA OVC039 18/16 A2994 KIAG 302000Z 35006KT 4SM -SHRA OVC031 22/21 A2996 KIAG 302100Z 27005KT 5SM BR BKNXXX 27/22 A29.95KIAG 302200Z 32010KT 5SM BR SCTXXX 2722 A29.95 • Buffalo: • KBUF 301800Z 23015KT 20SM SCTXXX 28/19 A2995 KBUF 301900Z 23017KT 9SM TSRA BKN040 27/21 A2994 KBUF 302000Z 25009KT 10SM BKN040 A2995 KBUF 302100Z 23010KT 9SM TSRA OVC040 25/19 A2993KBUF 302200Z 34005KT 10SM BKNXXX 26/20 A2996 Western NY Lake Erie Western NY Estimated location of lake breeze Boundary at 2130Z Lake Erie

  11. 30 July 1987

  12. 30 July 1987 Video of Tornado as it moved across parking lot Tornado 2) Keep your eyes on the Chevy Chevette 1) Watch for the car driving From Left to Right

  13. 30 June 2006 (Fast forward 19 years…) • ~1900Z: F1 Tornado in Cheektowaga • (about 3 mi from the BUF airport) • No fatalities • dollars damage??

  14. 30 June 2006 • 500 mb • Winds and Temp

  15. 30 June 2006 • 15 min Water Vapor with lightning (red) • 0945Z-1900Z (to time of F1) “The Canadian Export”: Notice the longevity of the storms as they move southeastward from Lake Huron into Southern Ontario

  16. 30 June 2006 • 15 min Water Vapor with lightning (red) • 0945Z-1900Z (time of F1) • Northwest Flow • (Almost) July • Shortwave • Look for lake breeze…

  17. 16Z 17Z 18Z • 1.5 Refl shows lake breeze boundary better than 0.5 slice Lake Ontario Southern Ontario Western NY Lake Erie

  18. 16Z 17Z 18Z • 1.5 Refl shows lake breeze boundary better than 0.5 slice Lake Ontario Southern Ontario Western NY Lake Erie

  19. 16Z 17Z 18Z • 1.5 Refl shows lake breeze boundary better than 0.5 slice Lake Ontario Southern Ontario Western NY Lake Erie

  20. 16Z 17Z 18Z • 1.5 Refl shows lake breeze boundary better than 0.5 slice Lake Ontario Southern Ontario Western NY Lake Erie

  21. 16Z 17Z 18Z • 1.5 Refl shows lake breeze boundary better than 0.5 slice Lake Ontario Southern Ontario Western NY Lake Erie

  22. 16Z 17Z 18Z • 1.5 Refl shows lake breeze boundary better than 0.5 slice Lake Ontario Southern Ontario Western NY Lake Erie

  23. 16Z 17Z 18Z • 1.5 Refl shows lake breeze boundary better than 0.5 slice Lake Ontario Southern Ontario Western NY Lake Erie

  24. 16Z 17Z 18Z • 1.5 Refl shows lake breeze boundary better than 0.5 slice Lake Ontario Southern Ontario Western NY Lake Erie

  25. 16Z 17Z 18Z • 1.5 Refl shows lake breeze boundary better than 0.5 slice Lake Ontario Southern Ontario Western NY Lake Erie

  26. 16Z 17Z 18Z • 1.5 Refl shows lake breeze boundary better than 0.5 slice Lake Ontario Southern Ontario Western NY Lake Erie

  27. 16Z 17Z 18Z • 1.5 Refl shows lake breeze boundary better than 0.5 slice Lake Ontario Southern Ontario Western NY Lake Erie

  28. 16Z 17Z 18Z • 1.5 Refl shows lake breeze boundary better than 0.5 slice Lake Ontario Southern Ontario Western NY Lake Erie

  29. 1.5 Refl shows lake breeze boundary better than 0.5 slice Lake Ontario Southern Ontario Western NY Lake Erie

  30. 1853Z1.5 Refl • 1847Z1.5 Refl • 1847Z1.5 SRM • 1853Z1.5 SRM

  31. 30 June 2006

  32. July 30 2006 and June 30 2006Tornado Track Comparison NWS BUF

  33. 1987 and 2006 Tornadoes in Cheektowaga, NYReason for similarities • Northwest flow aloft • Time of year • Climatology suggests July is the most active month for tornadoes over Western NY • (Short-wave) • Lake breeze boundary • These tornadoes probably take a local lake breeze circulation and tilt it into the vertical under a strengthening updraft • Non-descending tornadoes • very difficult to pick up on radar • Little or no lead time!

  34. 23 July 2006 • Minor Severe event • The “Canadian Export”: • A Strong outflow boundary moving into lake breeze front • Microburst over KIAG (Niagara Falls) • Funnel clouds

  35. 23 July 2006 • 500 mb • Winds and Temp • *Note: • The flow aloft doesn’t quite fit the Northwest flow definition • The trough is still upstream (instead of downstream) • Northwest flow definition fits for lower levels • (ex 550mb) • Trough Axis moving overhead

  36. Lapse Rates from RUC at 21Z

  37. 23 July 2006 • 15 min Water Vapor with lightning (red) • 1212Z-2045Z (to time of Severe Weather) “The Canadian Export”: Southern Ontario convection starts by 16Z and slowly moves southeastward, then interacts with lake breeze boundary along Niagara Peninsula and develops outflow boundary…

  38. 23 July 2006 • 15 min Water Vapor with lightning (red) • 1212Z-2045Z (time Severe Weather) “The Canadian Export”: Southern Ontario convection starts by 16Z and slowly moves southward, then interacts with lake breeze boundary along Niagara Peninsula and develops outflow boundary…

  39. 0.5 Velocity 0.5 Reflectivity Niagara Peninsula (Southern Ontario) Buffalo Airport Warning at 1933Z was issued With eye on outflow boundary Composite/lightning/Obs Southern Ontario Lake Erie

  40. 23 July 2006Funnel clouds, wind and ¾” hail • Trough Axis moving overhead • Developing Northwest Flow • July • Short-wave • Lake Breeze Boundary

  41. 28 July 2006 • One more case…. • Minor Severe event • Some wind damage.

  42. 28 July 2006 • 500 mb • Winds and Temp • *Note: • The flow aloft doesn’t quite fit the Northwest flow definition • The trough is still upstream (instead of downstream)

  43. 28 July 2006 • 15 min Water Vapor with lightning (red) • 1315Z-2200Z (to time of Severe Weather) “The Canadian Export”: Low topped convection develops with a shortwave around 17Z and moves, then interacts with lake breeze boundaries along Niagara Peninsula and near Niagara Falls area

  44. 28 July 2006 • 15 min Water Vapor with lightning (red) • 1315Z-2200Z (to time of Severe Weather) “The Canadian Export”: Low topped convection develops with a shortwave around 17Z and moves, then interacts with lake breeze boundaries along Niagara Peninsula and near Niagara Falls area

  45. 28 July 2006Wind Damage • Trough Axis moving through • July • Short-wave • Lake breeze front • This was a localized event • All activity died before it got to KBUF • Some enhacement possible due to extra low level moisture from morning precipitation.

  46. 30 June 2006 500mb Temp over KBUF: -17C Classic Northwest Flow Event 30 July 1987 500mb Temp over KBUF: -11C Classic Northwest Flow Event • 28 July 2006 • 500mb Temp over KBUF: • 7C • Trough Axis Event 23 July 2006 500mb Temp over KBUF: -14C Trough Axis Event

  47. Summary • A Mesoscale Severe weather effect: • Over Western NY, (primarily Niagara and Northern Erie Counties) Northwest Flow aloft combined with short-wave energy and sustained upstream convection, can combine with lake breezes, developing rapid intensification with a severe weather potential. Lake breeze circulations can spin up under updrafts to produce funnel clouds and occasionally tornadoes.

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