User:CapeVerdeWave/Random outbreak

The tornado outbreak of May 5, 1989, spawned sixteen tornadoes in Georgia, South Carolina, North Carolina and Virginia, and was responsible for a combined total of $169 million in damage in the four states. Population in some of the heavily-damaged areas has increased significantly since 1989, raising the potential costs of similar tornadoes, both in terms of monetary losses and lives.

Background
In the mid 1990s, the National Weather Service (NWS) undertook reforms that consolidated weather forecasting areas. At the time of the outbreak, however, several Weather Forecast Offices (WFOs) and smaller Weather Service Offices (WSOs) handled separate responsibilities within the same weather forecasting areas. While the mid 1990s coincided with the adoption of NEXRAD, weather radar in 1989 lacked Doppler technology. As a result, the WSR-57 and WSR-74 radars available to forecasters could not depict storm-scale mesocyclones and tornado vortex signatures. In some of the areas hardest hit on May 5, radars were quite distant from county warning areas and WSOs, hindering communications and the processing of data, so untimely delays frequently occurred during severe weather episodes. Typically, precise estimations of storm location and intensity could not be made or relayed on time, so the issuance of severe weather warnings often relied on visual observations of tornado and wind damage, as well as of unusual features such as funnel clouds. Due to these and other complications, tornado warnings often failed to precede large, intense, or damaging tornadoes.

Conditions on the morning of the outbreak contained contradictory signals as to tornado potential. At 8:00 a.m. EDT (12:00 UTC), a deep trough centered over the Midwestern United States induced separate bands of strong winds: one over the Ohio River valley and another over the lower Mississippi River valley. By 11:00 a.m. EDT (15:00 UTC), the latter occurred in association with a mesoscale convective vortex—a shallow, small-scale low-pressure area, called a mesolow, then crossing the middle of Mississippi. Based on data from on the morning radiosonde launched at 7:00 a.m. CDT (12:00 UTC) in Jackson, Mississippi, overall atmospheric instability was paltry over the warm sector, with most-unstable convective parcels (MUCAPE, or most unstable convective available potential energy) almost nonexistent, but wind shear, including low-level storm relative helicity (SRH) of up to 425 m2/s2, was ample for strong tornadoes. These parameters migrated northeastward with the progression of the mesolow, reaching northwestern Georgia by early to mid afternoon. A quasi-warm-frontal temperature boundary draped itself over western portions of the Carolinas. Anticipating gradual advection of a richer, more unstable air mass into the region, the National Severe Storms Forecast Center (NSSFC), today known as the Storm Prediction Center (SPC), issued a tornado watch effective as of 2:41 p.m. EDT (18:21 UTC) for northern and western areas of Georgia and South Carolina.

Conditions indeed became more favorable, and as supercells generated over the warm sector, developments spurred the NSSFC to issue a more strongly worded tornado watch—this time mentioning a Particularly Dangerous Situation (PDS), with the potential for intense, long-tracked tornadoes. The new watch encompassed most of South Carolina and significant portions of west-central North Carolina, effective as of 4:33 p.m. EDT (20:33 UTC). Several hours later, an radiosonde launched from Greensboro, North Carolina, in the evening indicated low-level SRH of 475 m2/s2, which was sufficient for powerful tornadoes and discrete supercells to form.

Non-tornadic effects
Large hail and wind damage reports were widespread - golf-ball sized hail was recorded near Columbia, South Carolina and Monroe, North Carolina, with severe wind reports from over 100 counties from Georgia to Maryland. Some form of storm damage was noted in almost every North Carolina county between I-95 and the Blue Ridge Mountains. Strong winds associated with the same squall line downed a radio transmission tower in nearby High Point. Winds toppled large trees and caused roof damage in the Emerywood neighborhood of the city.