Thunderstorm Gust Front passage with pink lightning at Coalville & Whitwick Weather Station - 17th August 2006

The forecasts earlier on this day threatened the possibility of disorganised storms. A few hundred j/kg of CAPE were expected to be present along with precipitable water values between 25 and 30mm. Lack of significant wind shear however, suggested the majority of storms would be disorganised. The first storm of the day occurred at around 1300Z which I didn't witness, but it did give a rainfall rate in excess of 100mm/hr. Thankfully, although I'd missed it, this was only to be the warm up.

As the evening approached the skies began to darken to the S and the big storm of the day announced intself with infrequent lightning to the S. As we moved towards 1900Z the lightning was becoming increasingly frequent and some low scud became visible which warranted further investigation. This was actually a nice mature gust front with a ragged shelf cloud. Of course the camera came out straight away, but lack of preparation and time had caught me out, so I had to shoot by hand rather than using the tripod. With the sky darkening and an unphotogenic foreground, getting good shots was something of a challenge, but the image below should give some idea of the drama as it approached.

As the gust front approached a distant roar became evident. I assumed this was a mixture of the wind and heavy rain associated with the gust front, but it nicely built the suspense as it became increasingly loud for a couple of minutes. When it hit it was clear a large part of the noise will have been from the pea sized hail that fell. If hail this size can cause hail roar, imagine what tennis ball sized hail must sound like rattling about in a supercell! Some very heavy rain was also accompanying the hail, to the point that the weather station recorded its highest rainfall rate to date - 234mm/hr - albeit only lasting a few minutes. Not the greatest of shots, but you can see the hail below:

The hail was actually deep enough to drop the temperature on the grass down to +0.6°C temporarily, but it didn't half leave a nice trace in the weather stations graphs. Although the air pressure didn't kick as it did in the storm earlier in the afternoon, the wind suddenly increased (bearing in mind the unfortunate sheltered location of the anemometer), air temperature, dew point and particularly grass temperature nose dived, whilst obviously the rainfall rate suddenly kicked up.

Thankfully I'd had the presence of mind to set my weathercam recording through all this, so here's some video footage to enjoy. Notice the lightning is pink because of the refraction of the light through the hail in the cloud. Bear in mind the video is farily large at 10MB, but worth a watch if you're in to storms. Just right click and save as to drop it down to your PC.

Gust Front Video - 10 minutes long, 10MB

Here's how the storm looked on radar at the time (images courtesy of Net Weather). Worth noting that rainfall rates are averaged over the 5km x 5km radar grid, so peak rainfall intensity appears to be no greater than 50mm/hr, yet my experience and my weather station clearly show it was much high if only for a short time.

I guess that you really had to be there, but it's nice to get a reminder every so often of what I love about weather!