At 3:44 p.m., the NWS issued a tornado warning for the city of Falls Church, southern Arlington county, the city of Alexandria, and eastern Fairfax county. Its warning statement said: “A CONFIRMED TORNADO WAS REPORTED NEAR FAIRFAX... AND WAS MOVING EAST AT 50 MPH. THIS TORNADO HAS BEEN CONFIRMED BY COUNTY OFFICIALS.”
After the storm passed, NWS conducted a post-storm assessment Saturday evening and was unable to identify damage consistent with the effects of a tornado:
TWO SURVEYS WERE CONDUCTED IN RESTON AND A THIRD SURVEY WAS CONDUCTED IN LORTON. THE NATIONAL WEATHER SERVICE HAS FOUND NO EVIDENCE OF A TORNADO AT THIS TIME.
NWS will only use the words “confirmed tornado” in a warning statement if it receives a report of a tornado on the ground from trusted sources, said Chris Strong, the warning coordination meteorologist at the Sterling NWS office. These sources include emergency management, law enforcement, trained storm spotters and NWS employees.
“We don’t take a general public report and take that report verbatim,” Strong said.
Saturday’s report originated from Fairfax County law enforcement officials, Strong said, but turned out to be second hand information.
At the time the report came in through its FEMA circuit - an internal communications line for emergency information - forecasters were told that law enforcement was reporting a confirmed tornado.
It was found after the event that, “Law enforcement had heard from the general public that there was a tornado,” Strong said.
Strong said the flawed report was “unfortunate” noting it’s common for the public to confuse straight line winds with tornado effects.
“There’s only so much fact checking you can do in a fast moving situation such as that,” Strong said. “There’s isn’t the time to fact check it vigorously.”