National Weather Service United States Department of Commerce

Severe Thunderstorm, Flash Flood and Heat Threats Lead up to Independence Day

Severe thunderstorms capable of mainly large hail and severe wind gusts are possible late this afternoon and into tonight over eastern Montana and parts of the western Dakotas. Excessive rainfall may result in flash flooding today over northern New Jersey, southern New York and western Connecticut. Heat Advisories have been issued today for the Twin Cities of Minnesota and the Artlatex region. Read More >

Slide 18

Lancaster, Texas Tornado of 25 April 1994

On 25 April 1994, an F4 intensity tornado struck the southern Dallas, TX suburb of Lancaster. The image on the right is a radar reflectivity image from the Fort Worth, TX WSR-88D at 937 PM CDT, and clearly shows a supercell thunderstorm moving eastward through the southern Dallas suburbs. The black line overlaid across the red area is the location of Interstate 20. The actual location of the tornado is south of the highway. However, this storm was also producing hail the size of golf balls. The area where large hail was falling was along the interstate highway, as depicted by the high reflectivities (dark reds) along I-20, to the north of the tornado path. Numerous drivers on I-20 that night stopped underneath bridges to shield themselves from the large hail, and in the process virtually stopped the flow of traffic on I-20.

This illustrates the potential for two things. First, this event occurred at night, with low visibility due to the hail and rain. In an event like this, oncoming traffic may not see the stopped traffic ahead and not have enough room to stop, thus causing a large traffic accident. This would be similar to accidents that occur in the Central Valley of California each winter owing to dense fog. And second, a several mile long path of stopped traffic, probably with thousands of people, was created just a few miles north of a violent tornado! Needless to say, had the tornado moved north or northeast instead of east, a parking lot of hundreds of vehicles, all with people inside, could have resulted in disaster.

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