The National Weather Service has concluded that marina damage on Lake Guntersville was due to a gustnado Saturday afternoon. A gustnado is a weak surface-based swirl of high winds that develops on a gust front: strong winds on the leading edge of rain and/or thunderstorms. Rapid changes in wind speed near the surface cause a 'spin' that occasionally develops into something like what you see below:
The National Weather Service's full report on the feature from Saturday is below:
Public Information Statement
National Weather Service Huntsville AL
1014 AM CDT Tue Apr 17 2018
...NWS Damage Survey for 4/14/18 Event...
...Marina Damage on Lake Guntersville Determined to be from
.Little Mountain Marina Damage...
Estimated Peak Wind: 90 MPH
Path length /Statute/: 400 Yards
Path width /Maximum/: 20 Yards
Start date: April 14, 2018
Start time: 211 PM CDT
Start location: 7 SW Langston, Marshall County, Alabama
Start Lat/Lon: 34.4594 / -86.1905
End date: April 14, 2018
End time: 211 PM CDT
End location: 7 SW Langston, Marshall County, Alabama
End Lat/Lon: 34.4589 / -86.1865
A very small path of damage was surveyed near the Little Mountain
Marina northeast of Guntersville. The path begins at the lake
shore where a tree was uprooted. Marina buildings suffered minor
damage; several windows were broken and some roofing was torn off
(which did not face the lake). Several tree branches were broken
and small tree trunks (all 6 inches in diameter or less) were
snapped, and a flagpole and a TV antenna were bent. The final
damage of note occurred near Murphy Hill Road, where two isolated
pine trees were snapped in a larger grove of pine trees.
Witnesses reported seeing a "waterspout without water" form over
Lake Guntersville and move ashore, causing the damage. Another
witness noted that the "waterspout" formed "along the cold
front". All of the eyewitness accounts note that it occurred
without any rain. Approximate timing given by witnesses suggests
that the event occurred between 1:30 and 2:30 PM.
Based on these eyewitness accounts and data from KHTX Doppler
radar, the damage is determined to be caused by a gustnado.
Gustnadoes occur along gust fronts, do not typically have a
condensation funnel, and are not associated with convective
cells (which were not present in the area during the time frame
mentioned). KHTX radar data show two gust fronts intersecting as
move across Lake Guntersville near the Marina at approximately
The National Weather Service would like to extend its appreciation
to local media outlets, eyewitnesses, and Marshall County
Emergency Management for their assistance.
The information in this statement is preliminary and subject to
change pending final review of the event and publication in NWS