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 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

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

Jul Aug Sep Apr May Jun NCEP/NCAR Reanalysis 500mb Geopotential Height Composite Mean

Other Factors 1.Northwest flow aloft 2.July 3.Short-waves in the cold upper level trough 4.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)

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

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

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

At the surface –Niagara Falls: KIAG Z 19016KT 12SM BKNXXX 29/21 A2995 KIAG Z 17011KT 4SM TSRA OVC039 18/16 A2994 KIAG Z 35006KT 4SM -SHRA OVC031 22/21 A2996 KIAG Z 27005KT 5SM BR BKNXXX 27/22 A29.95 KIAG Z 32010KT 5SM BR SCTXXX 2722 A29.95 –Buffalo: KBUF Z 23015KT 20SM SCTXXX 28/19 A2995 KBUF Z 23017KT 9SM TSRA BKN040 27/21 A2994 KBUF Z 25009KT 10SM BKN040 A2995 KBUF Z 23010KT 9SM TSRA OVC040 25/19 A2993 KBUF Z 34005KT 10SM BKNXXX 26/20 A July 1987 Estimated location of lake breeze Boundary at 2130Z Western NY Lake Erie Lake Ontario Southern Ontario Western NY Lake Erie Lake Ontario Southern Ontario

30 July 1987

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

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

30 June mb –Winds and Temp

30 June 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

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

1.5 Refl shows lake breeze boundary better than 0.5 slice Western NY Lake Erie Lake Ontario Southern Ontario 16Z17Z18Z

1.5 Refl shows lake breeze boundary better than 0.5 slice Western NY Lake Erie Lake Ontario Southern Ontario 16Z17Z18Z

1.5 Refl shows lake breeze boundary better than 0.5 slice Western NY Lake Erie Lake Ontario Southern Ontario 16Z17Z18Z

1.5 Refl shows lake breeze boundary better than 0.5 slice Western NY Lake Erie Lake Ontario Southern Ontario 16Z17Z18Z

1.5 Refl shows lake breeze boundary better than 0.5 slice Western NY Lake Erie Lake Ontario Southern Ontario 16Z17Z18Z

1.5 Refl shows lake breeze boundary better than 0.5 slice Western NY Lake Erie Lake Ontario Southern Ontario 16Z17Z18Z

1.5 Refl shows lake breeze boundary better than 0.5 slice Western NY Lake Erie Lake Ontario Southern Ontario 16Z17Z18Z

1.5 Refl shows lake breeze boundary better than 0.5 slice Western NY Lake Erie Lake Ontario Southern Ontario 16Z17Z18Z

1.5 Refl shows lake breeze boundary better than 0.5 slice Western NY Lake Erie Lake Ontario Southern Ontario 16Z17Z18Z

1.5 Refl shows lake breeze boundary better than 0.5 slice Western NY Lake Erie Lake Ontario Southern Ontario 16Z17Z18Z

1.5 Refl shows lake breeze boundary better than 0.5 slice Western NY Lake Erie Lake Ontario Southern Ontario 16Z17Z18Z

1.5 Refl shows lake breeze boundary better than 0.5 slice Western NY Lake Erie Lake Ontario Southern Ontario 16Z17Z18Z

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

1847Z 1.5 Refl 1847Z 1.5 SRM 1853Z 1.5 Refl 1853Z 1.5 SRM

30 June 2006

July and June Tornado Track Comparison NWS BUF

1987 and 2006 Tornadoes in Cheektowaga, NY Reason 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!

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

23 July 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

Lapse Rates from RUC at 21Z

23 July 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…

23 July 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…

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

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

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

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

28 July 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

28 July 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

28 July 2006 Wind 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.

30 July mb Temp over KBUF: -11C Classic Northwest Flow Event 30 June mb Temp over KBUF: -17C Classic Northwest Flow Event 23 July mb Temp over KBUF: -14C Trough Axis Event 28 July mb Temp over KBUF: -7C -Trough Axis Event

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.