van Dijke, Daniel, Clare Allen, Paul Knightley, Meteo
Group, Netherlands
On Monday 7th May 2012,
a single cell thunder storm which exhibited supercell characteristics formed
near Taunton, in south-west England around midday and tracked north-eastwards
for at least 5 hours over a distance greater than 150 miles. As it passed over
the county of Oxfordshire, tornado sightings were reported along with large
hailstones, rain and high straight-line wind speeds. Across the damage swathe
in which the tornado occurred, a number of buildings and trees were damaged,
including a school, whilst some farm out-buildings were completely destroyed.
The WRF forecast clearly showed a discrete propagating single cell thunder
storm with well defined rotation and clear inflow and outflow circulations. Well
defined classic supercell storms are unusual in the UK, and despite their
rarity the WRF model was highly successful at predicting the development,
evolution, propagation and the broad location of this storm.
In this presentation the
WRF forecast is compared with the actual observations of different sites and
radar data. It will show the quality of WRF in producing a supercell within the
model. The image shows the WRF output at 15 UTC. The red flag is the location
of the tornado. The wind field overlayed on the simulated radar reflectivity
shows supercell characteristics very nicely. WRF was the only model to come up
with this severity of the storm. Duty forecasters could use WRF to warn
different authorities for the thread on extreme hazardous weather. Even though
these types of events are rare in the UK, WRF did a good job representing.