1995 Mayfest Storm
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 NEXRAD radar image of the hailstorm at 6:56 p.m. CST, 14 minutes before striking the Fort Worth Mayfest | |
| Meteorological history | |
|---|---|
| Formed | May 5, 1995 |
| Hail storm | |
| Highest gusts | > 70 mph (115 km/h) |
| Overall effects | |
| Fatalities | 20 |
| Damage | $2 billion |
| Areas affected | Dallas–Fort Worth metroplex (Dallas, Parker, and Tarrant counties) |
The 1995 Mayfest storm was a damaging hailstorm that struck parts of the Dallas–Fort Worth metroplex on May 5, 1995. It was the first singular thunderstorm with a damage toll exceeding $1 billion and at the time the costliest nontornadic thunderstorm in U.S. history.[1] Hail up to 4.5 in (11.5 cm) in diameter fell across Parker and Tarrant counties, producing hail drifts as deep as 3 ft (0.91 m) and damaging numerous buildings. The storm also struck the Fort Worth Mayfest – a local outdoor festival – pelting the roughly 10,000 people in attendance with softball-sized hail and resulting in over 60 hospitalizations. Though there were no hail-related fatalities, the combination of the slow-moving supercell that produced the hail and a larger complex of storms led to deadly flash flooding that killed 17 people in the Dallas area. Overall, 20 people were killed by the storms.
A cold front had become stationary roughly 100 mi (160 km) south of the Dallas–Fort Worth metroplex by 7 p.m. CST on May 4, 1995. Weather models utilizing the concurrent weather conditions projected that the front would slowly recede northward over the course of May 5 in response to an approaching trough over the western U.S., while a nearby warm front would move north but remain well south of the metropolitan area. This depiction suggested that the associated thunderstorm potential for the region would peak after midnight on May 6. Accordingly, the National Severe Storms Forecast Center (NSSFC) and National Weather Service Fort Worth, Texas, both predicted that any severe weather on May 5 would be localized around the distant warm front to the south.[2]
Despite the model projections and weather forecasts, the warm front moved north faster than anticipated on May 5. This unexpected frontal progression was prompted by the arrival of a strong portion of a jet stream over Northern Mexico and Southwestern Texas in tandem with another trough. The front was farther north than predicted on the afternoon of May 5 and ultimately stalled just south of the Dallas–Fort Worth metroplex as the associated warm air butted against cool air associated with a mesoscale convective system over Oklahoma. The warm air mass exhibited convective available potential energy values near 2000 J/kg, indicative of an unstable environment. In response, the local NWS office began issuing forecasts highlighting the potential high wind and large hail for the Dallas–Fort Worth metroplex.[2]
In the early afternoon of May 5, a squall line developed along a dry line straddling the border between Texas and New Mexico. This cluster of thunderstorms moved east towards the Dallas–Fort Worth metroplex. The intersection of this squall line and the warm front led to the development of a mesolow that enhanced helicity nearby. Just after 5:30 p.m. CST, a high precipitation supercell formed roughly 40 mi (65 km) east of the squall line.[3][2] The storm quickly developed near the border between Palo Pinto and Parker counties and acquired supercell characteristics as it tracked across Parker County.[3][4] At 5:48 p.m. CST, the National Weather Service (NWS) issued a severe thunderstorm warning for Parker County.[5] As the storm moved into southeastern Parker County, it exhibited a hook echo and a pronounced bounded weak echo region on weather radar imagery. Hail began to fall from the storm by around 6:17 p.m. CST.[5] The mesocyclone associated with these radar features continued to produce a swath of large hail extending from southern Parker County into central Tarrant County, encompassing downtown Fort Worth.[2] The hailfall struck the Fort Worth Mayfest – an outdoor festival along the banks of the Trinity River – at around 7:10 p.m. CST.[6] The NWS issued a tornado warning on the storm at 7:06 p.m. CST for Tarrant County, though no tornadoes were ultimately reported.[5] A second mesocyclone developed as the storm moved over downtown Fort Worth, producing a second swath of large hail stretching from southern Fort Worth to Arlington. The storm slowed as it moved into Dallas County and ultimately merged with the approaching squall line to the west at around 7:30 p.m. CST.[2][1] The combined complex of storms slowed as a result of the merger, leading to extensive flash flooding in northern and central Dallas through 9:40 p.m. CST;[2] between 7:30 p.m. and 8:15 p.m., the forward speed of the storms decreased from 20 mph (30 km/h) to under 10 mph (15 km/h).[1] Rainfall rates in northern Dallas neared 9 in (23 cm) per hour, with rain gauge observations recording rates nearly three times heavier than that estimated by weather radar.[2] Rainfall amounts neared 2.25 in (57 mm) in 15 minutes.[6]
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