Late-May 1998 Tornado Outbreak and Derecho

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The Late-May 1998 Tornado Outbreak and Derecho was a historic tornado outbreak and derecho that began on the afternoon of May 30th extending throughout May 31st, 1998, across a large portion of the northern half of the United States (and southern Ontario) from southeastern Montana east and southeastward to the Atlantic Ocean. The initial tornado outbreak, including the devastating Spencer tornado, hit southeast South Dakota on the evening of the May 30th. The Spencer tornado was the most destructive and second deadliest tornado in South Dakota history. 12 people were killed; 6 by tornadoes and 6 by the derecho. Over 2 million customers lost power. Some had to go without power for up to 10 days.

1 Meteorological synopsis
2 Confirmed tornadoes
3 Spencer, South Dakota tornado
4 Southern Great Lakes derecho
5 New York tornado outbreak
6 See also
7 External links and sources

[edit] Meteorological synopsis

NWS damage survey map tracking the tornado families in southeast South Dakota

The first severe weather of the outbreak was reported at 12:30 p.m. in southeast Montana. Several hours later a supercell thunderstorm produced 2.75 inch (7 cm) hail across southeast Montana, kicking off the outbreak in earnest. Numerous reports of very large hail were received throughout the outbreak with the largest official report of 3.00 inches (7.6 cm) 10 miles (16 km) north of St. Lawrence in east-central South Dakota. The hail itself produced thousands of dollars in damage. Many reports of severe straight-line winds and damage were also reported. Numerous storm chaser reports suggest that significant severe weather events also occurred in the sparsely populated area traversed by the storm.

The family of tornadoes that crossed the Spencer area was observed by a Doppler On Wheels (DOW) radar (Wurman et al. 1997, Wurman 2001). The DOW observed the tornado or tornadoes from before 8:04 through 8:45 pm local time (01:04-01:45 UTC)(Alexander and Wurman 2005) and the tornado's passage through Spencer itself from 8:37-8:38 (01:37-01:38 UTC). DOW measurements of tornadic winds over the largely destroyed southern portion of Spencer have permitted the first (and only as of 12/2006) direct comparison of measured winds with F (or EF) Scale damage ratings as reported in the above referenced articles. Peak observed Doppler winds of near 115 m/s (258 mph) corresponded well with the documented F4 damage.

The DOW observations showed that the list of tornadoes derived from damage surveys alone, and the F-scale rating of that damage, may be incomplete and underestimate actual tornado intensity(Wurman and Alexander 2005). Single tornadoes may be mis-characterized as multiple tornadoes due to breaks in the observed damage.

DOW measurements suggest that the tornado may have a a multiple vortex structure as it crossed Spencer.

[edit] Confirmed tornadoes

Table of confirmed tornadoes - after surveys by local weather service offices

Confirmed Total	Confirmed F0	Confirmed F1	Confirmed F2	Confirmed F3	Confirmed F4	Confirmed F5
??	??	??	??	??	??	??

[edit] May 30 South Dakota event

F#	Location	County	Time (UTC)	Path length	Damage
South Dakota
F0	W of Lake Preston	Kingsbury	0002	unknown	First tornado touchdown. Short-lived with no damage.
F1	NW of Fulton	Hanson	0008	2 miles (3.2 km)	This was a fairly large and dusty tornado that affected mostly open ground in rural areas. It was the first tornado of the tornado family generated by the supercell that produced the Spencer tornado.
F2	NE of Fulton	Hanson	0016	6 miles (9.6 km)	Large tornado that produced minor damage, mostly remaining in open fields and trees. This was the second tornado of the Spencer tornado family.
F4	Spencer area	Hanson, McCook	0026	14 miles (23 km)	6 deaths - See section on this tornado
F1	SE of Alexandria	Hanson	0055	2 miles (3.2 km)	Tornado not related to the Spencer tornado family; it formed on a rear-flank downdraft (RFD) of the Spencer supercell and tracked roughly parallel to the south of that storm. Multiple major tornadoes from these two supercells were often ongoing and visible simultaneously. This tornado resulted in moderate damage to crops and several buildings.
F2	S of Salem	McCook	0056	6 miles (9.6 km)	Large tornado that resulted in significant damage to numerous farm buildings and houses, as well as extensive power line and crop damage. This too was a very large and strong tornado incurring about $1.0 million in damages to farm property, power lines, and crops. Tornado was 700 yards (650 m) wide.
F1	W of Emery	Hanson	0101	2 miles (3.2 km)	Related to the Alexandria tornado. Minor damage reported.
F1	W of Canistota	Hanson	0107	1 miles (1.6 km)	Final tornado from the Spencer tornado family. Significant damage reported to one farm.
F0	E of Emery	Hanson	0110	unknown
F1	E of Monroe	Turner	0125	1 mile (1.6 km)	Moderate property damage reported.
Sources: NCDC

[edit] Embedded in derecho

F#	Location	County	Time (UTC)	Path length	Damage
Wisconsin
F2	E of Menomonie	Dunn	0428	1 mile (1.6 km)	Three houses, including a mobile home, were destroyed. Heavy damage also reported on several farms. 8 people were injured.
F0	SW of Mosinee	Marathon	0621	200 yd (180 m)	Brief tornado embedded in the damage from the derecho.
F1	N of Stockbridge	Calumet	0720	1 mile (1.6 km)	Considerable damage reported in the area. Two barns were destroyed, along with a garage and silo. Damage also reported to one house.
Michigan
F0	SE of Lake City	Missaukee	0930	500 yd (450 m)	Numerous trees were snapped.
F0	Torch Lake	Antrim	0935	unknown	Brief tornado touchdown with minimal damage.
F1	N of Kalkaska	Kalkaska	0950	7 miles (11 km)	One mobile home was destroyed and two others were damaged. Extensive tree damage reported.
F0	N of Grayling	Crawford	0955	unknown	Brief tornado touchdown. One house sustained heavy damage.
F0	W of Flushing	Genesee	1025	unknown	Tornado confirmed amidst heavy derecho damage. Minor tornado-related tree and building damage.
Sources: NCDC

[edit] May 31 Northeast event

[edit] Spencer, South Dakota tornado

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The Spencer tornado then began at 7:26 p.m. 2 miles (3 km) north of Farmer in extreme eastern Hanson County and lifted at 7:52 p.m. 4 miles (6 km) southwest of Salem in McCook County, traveling 14 miles (23 km).

[edit] Southern Great Lakes derecho

This derecho got its start from a developing low pressure system that moved into the northern Great Plains and Great Lakes. The derecho formed from the same storm system that spawned the Spencer, SD Tornado, which killed six people. The supercell thunderstorm which produced that tornado transitioned into the derecho which killed another six people.

Late in the evening on the May 30, the tornado-producing supercells merged and became one squall line. It developed further and became a bow echo system.

It would become the most destructive natural disaster to hit the Upper Midwest in recent memory.

Timeline of the derecho

[edit] Minnesota

The most damage in Minnesota occurred at the northern edge in Sibley and McLeod Counties. Winds ranged from 80-100 mph in those two counties.

After the derecho raced through Minnesota, tens of thousands of trees were blown down. There were 500,000 customers without power. Over 100 homes were destroyed or damaged beyond repair. Twenty-two people were injured. The derecho caused $50 million in damage in southern Minnesota and northern Wisconsin.

[edit] Wisconsin

The derecho raced across Wisconsin in only three hours killing one person in Washington County when a tree fell through the roof and onto her bed where she was sleeping. It injured 37 people in Wisconsin. Many utility companies and emergency customers said that this was the most damaging straight-line wind thunderstorm event in 100 years. Five thousand homes and businesses were damaged and 24 were destroyed.

An area of south-central, south-east, and east-central Wisconsin reported wind gusts of over 100 mph (160 km/h) from this thunderstorm complex with an all-time official state record gust of 128 mph (206 km/h) 1½ miles (3 km) north-west of Lebanon in Dodge County. As with other derechos like the 4. July 1977 blow-down in northern Wisconsin, there were other unofficial reports of higher winds as well as estimates of such, including winds of 102 mph (165 km/h) sustained for a number of minutes and gusts up to 140 mph (225 km/h) also in Dodge County and/or adjacent sections of Fond du Lac County.

The derecho also caused boating accidents by generating a seiche on Lake Michigan which was reported to be around 10 feet (3 metres) high as it first struck the Michigan coastline of Lake Michigan further north in Muskegon County.

[edit] Central Great Lakes

The storm raced through Michigan in only two hours at an average speed of 70 mph. Four people were killed in Michigan, and 146 were injured. Total damage was estimated at $172 million (1998 dollars). 250 homes and 34 businesses were destroyed. In Grand Haven the Story & Clark smokestack at the Piano Factory Condominiums was destroyed when the force of the high wind caused it to crumble, and trees collapsed all over the city, some falling onto roofs. Damage in Spring Lake was worse, due to a highly localized zone of higher winds. The Mill Pointe Condominiums suffered serious damage, including the collapse of one unit. Others were subsequently removed. A factory lost its roof in the storm, and a number of businesses were damaged severely, one beyond repair. Country Estates Mobile Home park also suffered serious damage. A woman was killed in Pinconning, about 130 miles north of Detroit, when a tree fell on her house. Extensive damage to Grandville (approximately 30 miles inland) led to the city being closed off, with no traffic allowed to enter in the day after the derecho's passage.

This derecho would go on to break the record for biggest power outage ever in the state of Michigan (but later surpassed by the 2003 North America blackout). 860,000 people lost power, slightly more than the amount from the Southern Great Lakes Derecho of 1991. It blew down five 345-kilovolt transmission towers owned by Consumers Energy.

Thirteen counties in Central Lower Michigan were declared federal disaster areas.

One person drowned in Ontario when his boat turned over from the derecho's strong winds. Buildings in Toronto lost numerous windows and significant damage was observed in areas such as Trenton, Napanee, Picton and Kingston. Heavy thunderstorm activity was also reported in Ottawa and Montreal, Quebec but without damage.

It caused $300,000 worth of damage in central New York before reforming into a tornado outbreak at around 11 A.M. on May 31.

[edit] Summary

Overall, the derecho traveled 975 miles from southern Minnesota to central New York in 15 hours at an average speed of 65 mph. It became one of the most damaging derecho events in North America's history, causing $300 million in damage.

[edit] New York tornado outbreak

That afternoon, as the derecho dissipated, the cold front moved across farther east and broke up. The redeveloped system caused severe thunderstorms and tornados in Saratoga, Albany, Rensselaer, and Washington Counties in New York and Bennington County, Vermont.

The most destructive tornado of the day tore through Mechanicville and the adjacent town of Stillwater. It caused major damage to the town's old industrial section located on Route 4 and 32 along the Hudson River. One of the two historic smokestacks (visible from 2 miles away) was knocked down by the tornado. In 2005, the other smokestack and the conjoined building were bulldozed. The tornado was rated F3 on the Fujita scale.

[edit] See also

List of notable derecho events

[edit] External links and sources

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