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Robert J. Kuhn
There was a major outbreak of severe thunderstorms on June 02, 1998 over Southern Ontario. As a cold front swept in from the west, several severe thunderstorms developed over Southwestern Ontario, producing wind damage and hail in a number of localities as they tracked northeast towards the Muskoka and Eastern Ontario. Two of the supercells produced tornadoes during the mid to late afternoon, one of which caused extensive F1 to possibly F2 damage to buildings and trees in Norwich Ontario, and F1 damage in the Dunnville area. A second tornado touched down near Elmvale, causing F0 to F1 damage in that area. The thunderstorms moved out of Southern Ontario during the evening as the cold front swept into the northeastern US.
The synoptic situation was strongly favourable for the development and maintenance of severe thunderstorms on June 02, 1998. This case, in addition to the Sunday May 31, 1998 severe thunderstorm outbreak, was readily recognisable in the computer model forecast charts as long as three days in advance of the event.
|Warm and moderately unstable air quickly returned to Southern Ontario during the morning of June 02, in the wake of a warm front that produced a few showers and an isolated nocturnal thunderstorm. The warm sector was cloud free (Figure 1) allowing the strong sun to quickly heat up and destabilise the air thanks to a 45 to 50 knot southwesterly low level jet. A couple non-severe thunderstorms moved along with the low as it tracked across northern Lower Michigan during the morning, but conditions remained quiet in the warm sector as the airmass was capped.|
|Figure 1. Surface Analysis 02-June-1998 1200Z showing clear skies in warm sector.|
|By early afternoon (18Z) surface air temperatures had risen to 25 to 28°C with dewpoints near 14°C across most of Southern Ontario (Figure 2). The airmass had destabilised sufficiently for surface based CAPES to rise to near 1000 J/KG across Southern Ontario. However a 1°C cap near 850 mb was delaying the onset of any significant convection in the warm sector, allowing daytime heating to increase CAPES to as high as 2000 J/KG in areas near Lake Erie.|
|Figure 2. Surface Analysis 02-June-1998 1800Z.|
|While the airmass was destabilising during the early afternoon, dynamic support for long lived supercell thunderstorms was also rapidly increasing. A strong vorticity maximum and short wave trough (Figure 3) over Wisconsin at 12Z was expected to dig east-southeast to lie over Southwestern Ontario by 00Z June 03.|
|Figure 3. Strong vorticity maximum and short wave trough approaching Southern Ontario from the Midwest.|
Two strong westerly high level jets associated with the short wave trough passed over and just to the south of the Great Lakes by Tuesday evening, placing Southwestern Ontario under the left exit of the jet maximum over southern lower Michigan. Low and mid level wind fields also became increasingly favourable for long lived thunderstorms with a 50 knot southerly low level jet established over the eastern parts of Southern Ontario and a mid level 60 knot westerly jet passing over Western Lake Erie by evening, as shown in Figure 4. As a result favourable wind shears with storm relative helicities of 150-200 m2/s2 developed during the afternoon as the wind fields strengthened with the deepening low. With strong southwest winds enhancing low level moisture along the moist tongue crossing the area, and the strong mid level westerly jet bringing strong drying aloft during the afternoon, the environment quickly became favourable for the development and maintenance of long lived thunderstorms with potential for evolution into a squall line. The relevant severe thunderstorm parameters in this case are found in Table 1.
|Parameter||Value||Description or Result|
|Lifted Index LI||-4||Severe Tstms likely|
|George's K Index||near 35||60-80 % chance of Tstm
scattered to numerous tstms
|CAPE||2000 J/KG||Cb tops to 40000 feet
|Storm Relative Helicity||150-200 m2/s2||Weak mesocyclone
F0 - F1 tornado possible
|Wind Shear Sfc - 3 km(Metric Wind Shear)||50 knots 10 ms-1km-1||Favourable for long lived thunderstorm cells|
|Bulk Richardson Number||40||Spring Classic Low Topped
Supercells-possible evolution into squall line
Table 1. Some Summer Severe Weather Parameters of the Norwich and Elmvale Tornado Producing Thunderstorms.
|A severe thunderstorm threat box encompassing much of Southern Ontario and the neighbouring states was shown on the severe weather forecast chart valid at 00Z 03-June-1998 (Figure 5). The threat of severe thunderstorms was greatest in Niagara and Haldimand-Norfolk near the east end of Lake Erie where more daytime heating and moisture from the south increased CAPES in the airmass to as high as 2000 J/Kg.|
|Figure 4. Severe Weather Composite Chart Valid 00Z (8.00 PM EDT) 03-June-98|
|Damaging winds and large hail were the main threats in these thunderstorms, along with the possibility of an isolated tornado especially in the Niagara and Haldimand Norfolk regions where higher instability would permit formation of tornado producing supercells. The severe thunderstorm threat box encompassed all areas which had favourable conditions for the development of severe thunderstorms between 18Z (2.00 PM EDT) 02-Jun-98 and 06Z (2.00 AM EDT) 03-Jun-98. All that was needed to initiate thunderstorm development was a trigger.|
|Figure 5. RCTO Severe Weather Chart showing severe thunderstorm threat areas valid 18Z 02-Jun-1998 to 06Z 03-Jun-1998.|
Brief Description of the Thunderstorms
|The morning of 02-Jun-1998 was fairly quiet with the only significant convection being a few thunderstorms near the low and cold front moving from Lower Michigan over Lake Huron. However, as seen in Figure 6, thunderstorms suddenly developed along a convergence line extending northeast from the Rondeau area of Lake Erie to north of London then on to the Mount Forest area. It appears that lake breeze convergence played a part in the initial trigger of the thunderstorms, even though convergence was not evident on the streamline charts at the time.|
|Figure 6. Visible Satellite Photo showing initiation of convection over Southwestern Ontario at 1845Z June 02, 1998. Lake breeze convergence near and north of the shore of Lake Erie (A) in the southwesterly flow appears to be triggering development of convective clouds at this time.|
|Figure 7. Visible Satellite Photo showing tornado producing thunderstorm (A) over Norwich at 2010Z (4.10 PM). A second supercell (B) produced a tornado that touched down near Elmvale, north of Barrie about the same time.|
|Figure 8. Exeter Radar imagery showing a tornado producing supercell thunderstorm (A) over Norwich and a second tornado producing thunderstorm (B) just east of Elmvale at 2010Z (4.10 PM).|
The thunderstorms intensified rapidly, with cells quickly becoming severe just southeast of London and to the west of Barrie by 2000Z (4.00 PM EDT). Figures 7 and 8 show how quickly the thunderstorms intensified, with the thunderstorm passing over Norwich quickly attaining supercell characteristics.
|As seen in Figure 9, the supercell passing over Norwich was clearly the strongest, and it had the highest tops at over 14 km. The supercell, which has just passed over Elmvale, wasn't as high as the Norwich storm, with one pixel showing radar echo tops of above 12 km as seen in Figure 9. Other thunderstorms also had high radar echo tops (Figure 9), with associated strong winds and large hail as discussed below.|
|Figure 9. King Radar Echo tops image from 2010Z. The thunderstorm (A) over Norwich had the highest radar echo tops (above 14 km) at the time, while the thunderstorm (B) which had just passed over Elmvale had lower radar echo tops (above 12 km). Other thunderstorms such as C also had high echo tops, and severe weather associated with them.|
|Interestingly enough, there was little or no lightning observed on the lightning detector network from this thunderstorm when the tornado struck Norwich (Figure 10), while abundant lightning strikes were detected from the Elmvale thunderstorm. Most of the other thunderstorms also had much lightning associated with them.|
|Figure 10. Lightning Strike data at 2010Z for previous 10 minutes. Note lack of lightning strikes at the time from the Norwich storm.|
Severe Weather and Damage from the Thunderstorms
There were a number of reports of wind damage, torrential downpours and funnel clouds associated with the thunderstorms, in addition to the two tornado producing supercells and two reports of large hail (Table 2). Wind damage was by far the most common type of severe weather report.
|Event Type or Damage||Location||Time (EDT)|
|140 km/h wind
|Petrolia (SE Sarnia)||2.30 PM|
|100 km/h wind||Brussels (Huron County)||2.45 PM|
|Trees down||Exeter (50 km N London)||2.45 PM|
|2 cm hail||Hanover||3.45 PM|
Extensive damage to trees, buildings, farm machinery
|Trees and hydro poles down
Garage roof ripped off
|Funnel cloud||Woodstock||4.00 PM|
Extensive damage to houses, church, and trees
|Trees down||Cambridge||4.10 PM|
|Trees down||Thornbury (E Owen Sound)||4.10 PM|
|Funnel cloud||Alliston (SW Barrie)||4.11 PM|
|51 knot wind gust||Muskoka Airport||4.20 PM|
|Funnel cloud||Orillia||4.30 PM|
|Trees, power lines down||North York||4.50 PM|
Much damage to farms
|Balmoral - Dunnville||4.50 PM|
|Trees, power lines down||Hamilton||5.00 PM|
|Possible tornado||Simcoe||5.15 PM|
|2.1 cm hail||Richmond Hill||5.25 PM|
|Trees, power lines down||Crystal Beach, Fort Erie||5.40 PM|
|Trees down||Just North of Port Hope||6.30 PM|
|Trees down||Sharbot Lake (50 km N Kingston)||6.40 PM|
Table 2. Reports of severe weather and damage from the thunderstorms on June 02, 1998. Damage is from straight line winds unless noted.
|Most of the thunderstorms raced from the southwest to the northeast, carried by the strong southwest winds aloft. However, the Norwich thunderstorm and tornado tracked east-southeast towards Dunnville (Figure 11), with tornado damage evident as the tornado skipped along the track. The thunderstorm then weakened slightly, but still produced straight line wind damage intermittently as far as the Fort Erie and Crystal Beach areas later in the afternoon, before passing into Western New York State over Buffalo. The storm then intensified again, producing another tornado southeast of Buffalo later in the day.|
|Figure 11. Severe Thunderstorm Tracks and associated damage on June 02, 1998.|
It also appears that the Elmvale tornado producing thunderstorm tracked eastward a short distance, before weakening somewhat then racing northeast towards Muskoka Airport, where 100 km/h winds and hail were reported.
|There were several other severe thunderstorm tracks (Figure 11) as well on June 02. These thunderstorms had supercell characteristics at times as seen on radar and satellite, and produced straight line wind and hail in a number of areas.|
|Figure 12. Tornado observed over Norwich near 4.00 PM June 02.|
|However most of the damage was from the tornadoes that touched down in Elmvale, and in the Norwich to Dunnville track. There was extensive damage in both places, mainly to buildings, trees and farm implements. For example, shortly after the tornado was seen and photographed in Norwich (Figure 12), a church was destroyed (Figure 13) along with severe damage to many neighbouring homes and trees. Figure 14 shows a small barn near Norwich having been impaled by a tree limb from the tornado.|
|Figure 13. Piano and other furniture thrown out of destroyed Church in Norwich.|
|Figure 14. Barn near Norwich impaled by a tree limb.|
|The Elmvale tornado was responsible for considerable damage to buildings, trees and farm equipment, as seen in Figures 15, 16 and 17.|
|Figure 15. Damage to farm equipment near Elmvale. ¾ inch steel bolts were sheared, detaching a steel support leg from the silo.|
|Figure 16. Damage to a barn near Elmvale.|
|Figure 17. Downed trees and damage to a house near Elmvale.|
Watch and Warning Progression and Verification
As mentioned before, the synoptic situation leading to the severe thunderstorms and tornadoes of June 02 was hinted at in the guidance a couple of days prior to the event. After a quick assessment of the situation, a severe thunderstorm watch covering parts of Southern Ontario along and southeast of a line from Brantford to Waterloo to Barrie-Huronia was issued just before 9.00 AM. Upon completion of the severe weather assessment, the watch was then extended to cover remaining parts of Southern Ontario along and south of a line from Barrie-Huronia to Lanark County (just south of Ottawa).
Table 3 contains a summary of the watches and warnings issued across Southern and Eastern Ontario for this event.
Table 3. Summary of Severe Thunderstorm and Tornado Watches and Warnings
|Bulletin||Issue Time (EDT)||Description||Verification|
|Severe Tstm Watch||8.52 AM||Southern Ontario SE of a line from Brantford-Waterloo-Barrie-Huronia||Hit|
|Severe Tstm Watch||10.52 AM||Rest of Southern
Ontario except for
|Hit except false
alarm for Windsor area
|Severe Tstm Wrng||1.08 PM||Waterloo-Wellington-Dufferin||False Alarm|
|Severe Tstm Wrng||2.14 PM||Peterborough-Kawarthas-Trenton||False Alarm|
|Severe Tstm Watch||2.45 PM,
|Eastern Ontario except Ottawa, Cornwall||Hit|
|Severe Tstm Wrng||3.01 PM||Huron-Perth||Hit|
|Severe Tstm Wrng||3.08 PM||Grey-Bruce||Hit|
|Severe Tstm Wrng||3.41 PM||Southern Ontario SE of a line from London to Barrie||Hit|
|Tornado Wrng||3.50 PM||Barrie-Huronia, Halton-Peel, York-Durham, Waterloo-Wellington-Dufferin||Hit for Huronia
False alarm elsewhere
|Tornado Wrng||4.06 PM||Brantford-Haldimand- Norfolk, Hamilton-Wentworth, Niagara||Hit except false alarm for Hamilton-Wentworth|
|Severe Tstm Wrng||8.14 PM||Prince Edward County||False Alarm|
|Severe Tstm Wrng||9.03 PM||Kingston-Brockville, Frontenac-Lanark||Hit|
Severe thunderstorm warnings for the Waterloo and Peterborough areas were issued early in the afternoon, as strong thunderstorms suddenly developed and raced through these areas. However they weakened quickly, and these warnings turned out to be false alarms.
However, even stronger thunderstorms formed suddenly over Southwestern Ontario during the middle of the afternoon, spawning a number of warnings as shown in Table 3. Several of the thunderstorms quickly attained supercell characteristics, with numerous mesocyclone alerts on the King City Doppler Radar from the tornado producing thunderstorm that passed over Elmvale. Unfortunately, the Norwich tornado producing thunderstorm was just beyond the King City Doppler radar range. However, conventional radar from Exeter showed supercell characteristics including a bounded weak echo region, and overshooting tops in this long lived severe thunderstorm.
Severe thunderstorm watches were issued about 4 to 6 hours before the event. Severe thunderstorm warning lead times ranged from short fuse zero lead times to about 90 minutes. Tornado warnings were issued either upon receipt of tornado touchdown information such as was the case in Norwich, to about 60 minutes in advance of the event such as for the tornado touchdown near Dunnville. Doppler radar imagery was available for the Elmvale tornado, and was an important information source involved in the issuance of the tornado warning about 5 minutes in advance of the event for that region.
All the watches and warnings were discontinued in the evening as the thunderstorms and cold front raced off to the east of the district into New York State and Quebec.
Severe thunderstorms developed rapidly over Southern Ontario during the afternoon of June 02, 1998. Two of the thunderstorms spawned tornadoes, with F1-F2 tornado damage being reported along a line from Norwich to Dunnville, and F1 tornado damage being reported in the Elmvale area in Simcoe County. Straight line wind damage and large hail were observed in a few other severe thunderstorms crossing the district.
Lake breeze convergence, along with convergence from an approaching cold front, appear to be major factors in the sudden formation of these severe thunderstorms. The favourable severe thunderstorm environment was recognised as far as a couple of days in advance of the event, allowing for issuance of severe thunderstorm watches some 4 to 6 hours prior to their development. Severe thunderstorm warnings and tornado warnings were generally well handled, with lead times ranging from zero to 90 minutes for the severe thunderstorm warnings, and zero to 60 minutes for the tornado warnings.
All watches and warnings were discontinued during the evening as the thunderstorms and cold front raced to the east of the district.
Written by Robert J. Kuhn.
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Last Modified: May 27, 1999
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