After the highest temperature recorded in the UK since July 2015
was recorded, a News
Release from the Met
Office described how the hot conditions would end in a bang, with intense
thunderstorms forecast.
Summer
showers and
thunderstorms are notoriously difficult to forecast, we know if the conditions
are right for them to develop, but predicting the exact time and location can
be likened to trying to predict bubbles in a pan of boiling water! That said,
thanks to WOW observations, Meteorologists now have one more
tool to help predict when and where damaging thunderstorms are likely to occur.
High
resolution surface analyses, which include input from WOW observations, were being trialled by Met Office Meteorologists to help
inform where thunderstorms were most likely to break out on the 26th
and 27th July. The thunderstorms on the 27th July produced damaging
winds and hail across Eastern England.
26th
July
These plots,
based on data from WOW observations, are from the afternoon of 26th
July. The shading shows surface temperatures, the lines are surface pressure, and
the arrows are wind vectors. A growing area of cooler air and higher pressure can be
seen over North East England. This was a ‘cold pool’ associated with an area of
thunderstorms, which can be seen on this rainfall radar image from around the
same time:
Cooler,
denser, air from the downdraught of a thunderstorm meeting warmer air at the surface
can lead to further developments. The thermal boundary between cooler and
warmer air highlighted on the plots from the WOW observations pinpointed where
further heavy showers and thunderstorms would develop over the coming hours. An
hour later the thunderstorms had developed further and the radar image looked like this:
27th
July
These plots from July 27th show convergence, where air travelling in
different directions meets (converges) and is forced to rise. Rising air is one
of the ingredients for heavy showers and thunderstorms. The pink areas over East
Anglia and Lincolnshire on the plots, which are again based on WOW data,
highlighted an area likely to see thunderstorms develop on the 27th.
Thunderstorms were expected to develop here once the temperatures were high
enough for them to do so. Reaching a certain ‘trigger’ temperature is often
another ingredient for thunderstorm development.
Nothing can be
seen on the radar image over East Anglia in the morning, but by late afternoon intense thunderstorms had developed in this area:
There were other
factors that led to the development of these thunderstorms, in addition to
those discussed above, and Met Office Meteorologists would have been using all
the different sources of information available to them to monitor the
situation. The analyses drawn up from the WOW observations are just one of many
tools our Meteorologists use, but the observations provided by our voluntary
observers are certainly being put to good use.
