Late-May 1998 Tornado Outbreak and Derecho

The Late-May 1998 Tornado Outbreak and Derecho was a historic tornado outbreak and derecho that began on the afternoon of May 30 extending throughout May 31, 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 30. 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 two million people lost electrical power, some for up to 10 days.

The derecho was the most violent line of thunderstorm observed on earth during the 1998 calendar year according to the National Weather Service review shortly after the year was over.Fact|date=August 2007 It was also the climax of an unusually heavy derecho season in the North-Central United States and adjacent parts of Canada and the Northeast U.S., and this storm combined the characteristics of the two major forms of derecho, the serial and progressive derecho. At various points of its evolution, it displayed textbook and/or record manifestations of supercell and derecho-related phenomena such as the right-mover supercell, evolution of supercells into a linear mesoscale feature which rapidly became a derecho, cumulonimbus with overshooting top and dome, bow echo, bookend vortices, regular and rotor downbursts, gust front, gustnado, rear inflow notch, classic derecho radar signature, effects of infrasound and atmospheric electricity, haboobs, and wind effects on bodies of water including seiches and exposure of bottoms of water features by the wind. The disturbance which was originally the derecho finally disappeared off the coast of Norway more than a week later.

Meteorological synopsis

The first severe weather of the outbreak was reported at 12:30 pm in southeast Montana. Several hours later a supercell thunderstorm produced 2¾ 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 inches (75 mm) 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 pm (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 multiple vortex structure as it crossed Spencer.

Confirmed tornadoes

May 30 South Dakota event

ummary

Overall, the derecho traveled 975 miles (1560 km) from southern Minnesota to central New York in 15 hours at an average speed of 65 mph (104 km/h). It became one of the most damaging derecho events in North America's history, causing $300 million in damage.

Northeastern North America tornado outbreak

That afternoon, as the derecho dissipated, the outflow boundary moved into a very warm and unstable airmass which was in place (CAPE was above 2400 J/kg). Thunderstorms developed along this boundary and quickly became severe. One particularly severe thunderstorm which later went on to produce an F3 tornado in Mechanicville, NY developed at 4:02 pm. At 4:12 pm, the storm shows strong rotation with 64+ kt (33+ m/s) winds at 5,000 feet in the mesocyclone. At 4:15, this storm produced 1 inch (25 mm) hail and a 52 mph (23 m/s) wind gust. At 4:17 pm, rotation increases, and at 4:20 pm the storm produced 1¾ inch (45 mm) hail. At 4:22 pm, Albany Doppler radar shows a strong and deep TVS, with 105+ kt winds. This is also the same time a tornado is reported on the ground.

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.

Several other tornadoes touched down across New York and Pennsylvania with one of the tornadoes causing a fatality in the Salisbury, Pennsylvania area. [ [http://www4.ncdc.noaa.gov/cgi-win/wwcgi.dll?wwevent~ShowEvent~338242 NCDC: Event Details ] ] Another tornado caused major damage to the town of Lyons [ [http://www4.ncdc.noaa.gov/cgi-win/wwcgi.dll?wwevent~ShowEvent~338246 NCDC: Event Details ] ] while another caused major damage around the Binghamton Metro Area including TV station WIVT sustained heavy damage which forced them to be off the air for several months. [ [http://www4.ncdc.noaa.gov/cgi-win/wwcgi.dll?wwevent~ShowEvent~331829 NCDC: Event Details ] ] Activity ceased late in the evening across the southeastern portion of Pennsylvania. A total of 41 tornadoes were confirmed during the post-derecho outbreak.

Confirmed tornadoes

May 31 New York event

ee also

*List of North American tornadoes and tornado outbreaks
*List of derecho events

References

External links

* " [http://www.crh.noaa.gov/mpx/?n=derechoevent Origins And Synoptic Setting For The 30- 31 May 1998 Minnesota To New York Derecho] " (NWS Twin Cities, MN)
* " [http://www.spc.noaa.gov/misc/AbtDerechos/casepages/may30-311998page.htm The Southern Great Lakes Derecho of 1998] " (Storm Prediction Center)
* [http://www.erh.noaa.gov/er/bgm/WeatherEvents/Severe/may311998/ 10-Year anniversary page of the outbreak (NWS Binghamton)]
* [http://www.erh.noaa.gov/er/aly/Past/1998/may31a/may31.htm 10th Anniversary page from the NWS Albany]
* " [http://www.cnn.com/WEATHER/9805/31/midwest.storms/index.html Upper Midwest hit by hurricane-force storm] " (CNN)
* [http://www.stormeyes.org/tornado/spencer/ Detailed SPC overview]
* [http://www.crh.noaa.gov/fsd/storms/spencer/ NWS overview]
* [http://cimss.ssec.wisc.edu/goes/misc/980530.html CIMMS satellite imagery and meteorological analysis]
* [http://www.cswr.org/projects/rotate/spencer.html CSWR Doppler-on-wheels Spencer page]
* [http://www.nws.noaa.gov/om/assessments/spenccov.htm DOC-NOAA-NWS Service Assessment]
* [http://www.sdpb.org/net/oto/spencer/ Informative South Dakota Public Broadcasting website]
* [http://www.geocities.com/sunsetstrip/alley/8239/spencer.html Andy Schmidt's Spencer website with tornado and damage photos and aftermath information]
* [http://www.cnn.com/US/9806/01/s.dakota.tornado/ Original CNN Spencer report]
* [http://www.cnn.com/US/9806/01/storm.roundup/ CNN report on entire outbreak]