What Happened? Late-Night Sirens Warrented?

(Sunday, July 5, 2009) – At 12:33 AM, the NWS in Memphis issued a tornado warning (see text below) that included Madison County.  This was based on the rotational signature (see radar image below, note the yellow circle) that was near Cedar Grove in Carroll County.  In the radar image the green against the red in the image was a rotational signature that prompted the warning.  The NWS uses a “storm-based” polygon warning system in which the polygon now projects the path and areas that could be affected by the storm.  This polygon picked up the NE corner of Madison County.  Thus the sirens were triggered. 

At 12:49 AM, the warning was cancelled for Madison County (see text below).

1233 AM CDT SUN JUL 5 2009

THE NATIONAL WEATHER SERVICE IN MEMPHIS HAS ISSUED A

* TORNADO WARNING FOR…
  SOUTHWESTERN CARROLL COUNTY IN NORTHWEST TENNESSEE…
  HENDERSON COUNTY IN SOUTHWEST TENNESSEE…
  NORTHEASTERN MADISON COUNTY IN SOUTHWEST TENNESSEE…

* UNTIL 115 AM CDT

* AT 1234 AM CDT…NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A SEVERE THUNDERSTORM PRODUCING A TORNADO 8 MILES NORTH OF BLUE
  GOOSE…OR 10 MILES SOUTHEAST OF MILAN…MOVING SOUTHEAST AT 20 MPH.

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1249 AM CDT SUN JUL 5 2009

…THE TORNADO WARNING FOR NORTHEASTERN MADISON AND SOUTHWESTERN
CARROLL COUNTIES IS CANCELLED…

AT 1248 AM CDT…WEATHER SERVICE DOPPLER RADAR INDICATED THAT THE THUNDERSTORMS WHICH PROMPTED THE WARNING HAVE MOVED OUT OF THE AREA
…AND NO LONGER POSE AN IMMEDIATE THREAT TO LIFE OR PROPERTY. THEREFORE…THE TORNADO WARNING IS CANCELLED.