The first indications of trouble came early on Sunday morning, April 27, 2002. The Storm Prediction Center in Norman, Oklahoma issued an Outlook for a Moderate Risk of Severe Weather across a large portion of the Mid Atlantic and Northeast as a strong low pressure system moved eastward from the Great Lakes. Accompanied by strong upper level winds, the low pressure system was forecast to cause widespread wind damage. Later outlook continued to emphasize the threat and began to mention the possibility of tornadoes. Persistent cloudiness during the late morning led forecasters to downgrade the threat to slight by noon.
But by early afternoon, the severe weather outbreak was underway and a PDS (Particularly Dangerous Situation) Tornado Watch was issued for portions of Kentucky, Virginia, West Virginia and western Maryland. At mid-afternoon, the severe weather threat was upgraded back to moderate for Maryland and the Mid Atlantic with the threat of tornadoes prominently mentioned. A new tornado watch was issued for most of Maryland at 3:05..
At 6:45 p.m. the NWS Baltimore/Washington office issued a severe thunderstorm warning for a supercell storm moving into Charles and Calvert Counties in Maryland from Virginia. On radar, the storm appeared to be weakening, but a piece of critical information had not been relayed to them: that the same storm had produced tornadoes around 5 p.m. while it was still across the state line. In addition, forecasters were not dividing up duties so that different teams were monitoring individual storms. These factors, along with a fear of crying wolf, led the forecasters to stop short of a tornado warning. As the supercell crossed the Potomac River, it rapidly intensified. At 6:56, the tornado touched down west of La Plata. At 7:00 p.m., forecasters decided to upgrade the warning and were attempting to call the EOC in La Plata, but lines were already jammed with reports of the tornado. When the forecasters finally made reached the 911 center, they were told that the tornado was already doing damage. The tornado caused its first fatalities in at 7:10 p.m. The tornado would remain on the ground for 30 miles, all the way into Calvert County. F4 damage was reported along the path near La Plata. 4 people died and over 100 were injured by the devastating storm. Originally classified as an F5, later damage surveys downgraded the damage to that equivalent to an F4 tornado, one of only three F4 tornadoes ever in Maryland.
The lessons learned are not new: established office policies must be followed to facilitate communication of critical information and ensure proper storm monitoring. Supercells often display cycles of weakening and intensification. Forecasters should always be slow to downgrade from a tornado warning. The severe thunderstorm warning issued at 6:45 did carry the familiar line “Severe thunderstorms can produce tornadoes with little or no advance warning.” This is important advice for all of us whenever severe thunderstorm warnings are issued. When it comes to thunderstorms, expect the unexpected!
