Wake-Franklin tornado survey

The Raleigh National Weather service office has completed and issued a storm damage survey for the severe thunderstorm that occurred Sunday night, April 25, 2010, along a track stretching across Wake, Franklin, Nash and (as it weakened) Edgecombe counties, and I've included the complete text of the report at the end of this post.

This was an especially interesting scenario, with the atmosphere in a pattern that was supportive of a slight risk of severe storms, but with activity greatly suppressed by the arrival of very dry air aloft earlier in the day. Toward evening, a very small shower/thunderstorm cell formed up just west of Wake County and tracked east-northeast, behaving in a quite benign fashion until suddenly intensifying and taking on a rotating, supercell structure just before 8 pm as it moved into easternmost parts of Wake County. From there into at least central Nash County, the storm showed a classic "hook echo" form in it's radar reflectivity and also signs of notable low-to-mid level rotation in Doppler velocity displays, as seen in some of the images I captured after the fact from the radar archive page at Plymouth State University.

I also included an image from the Iowa Environmental Mesonet County Warning Verification site that illustrates the application of "storm-based" warnings by the NWS. As you'll see, the warning area is much more confined to expected track of the storm in question than the older county-based warnings. Note that those are still in use for NOAA weather radios, so anyone in any part of Wake, Franklin or Nash county would have received an alarm. Also note that rather than being a simple trapezoid, the warning area has a small "notch" toward its southwestern corner. This is included to prevent all weather alarm radios in Johnston county from sounding an alert, since the tornado was considered likely to stay just north of the county line. While weather radio remains a very valuable system, this situation also highlights the benefits of a service like WeatherCall, which would only relay telephone warnings to addresses that fall within the red boxes outlining each storm-based warning update.

It is worth noting that in this case, the sudden development and reorganization of the storm and its rapid production of a weak tornado made it nearly impossible to project that a tornado would form from this cell, and meant that a tornado was already reported on the ground around 5-8 minutes before the first warning was disseminated, so that a funnel cloud or tornado likely crossed a small area west of the starting location of the warning box before any kind of warning was in place. Therefore, some owners of weather radios or subscribers to WeatherCall saw the funnel but did not hear an alarm until a bit later (weather radio) or did not receive a WeatherCall due to living at an address that was a short distance west of the beginning of the warning area. In many other cases, storms will show some signs of potential tornado production prior to a tornado forming, allowing for warnings to provide somewhat more in the way of advance notice.

As you may have already seen, this system was photographed by many of our viewers. There are also at least a couple of good videos of the tornado on YouTube, and I've included links to those here. As you'll see in the report below, this tornado was rated at EF-0, with a track about 75 yards wide by 3.5 miles in length and maximum winds estimated around 80 mph.

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400 PM EDT MON APR 26 2010

COUNTIES NORTH CAROLINA...

INJURIES...0

FRANKLIN COUNTY NORTH CAROLINA ON APRIL 25 2010.

CENTER WERE AROUND 70 MPH.

WHICH FELL WERE LARGE HARDWOOD TREES BETWEEN 3-4 FEET IN DIAMETER.

COUNTY THEN LIFTED OFF THE GROUND.

AND THE MAXIMUM WIND SPEED WAS AROUND 80 MPH.

WINDS NEAR SPRING HOPE WERE ESTIMATED AROUND 65 MPH.

THIS INFORMATION CAN ALSO BE FOUND ON OUR WEBSITE AT WEATHER.GOV/RAH.

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