Gustnadoes and Shelf Clouds - 24th May 2018
May 24th involved a storm chase in north-west Kansas - after driving south from North Platte, Nebraska, we took up residence to the north of Oakley, Kansas just to the north of I-70 - where there was an agitated cumulus field developing just to the west. We sat in the same location for over 3 hours, watching the cumuli slowly bubble and gradually become more vertically extensive. Some cumulonimbi developed right on top of us, and we waited patiently as they slowly grew, throwing out deep rumbles of thunder all the while.
Surface weather map, valid for 10:00 (Central Time) on the 24th May 2018. All of the Plains sit in the broad warm sector of a weak surface cyclone located over the Canadian praries. Weak moisture advection from the Gulf resulted in dewpoints in the mid to high 60s Farenheit. 
Credit: NOAA/Weather Prediction Center.​

SPC convective outlook issued at 11:42 CDT. A slight risk was issued for the Northern and Central High Plains. Tornado risk remained below the 2% threshold. 
Credit: Storm Prediction Center.

The first cumulonimbi of the day. This storm eventually developed after we waited for over three hours for the cumulus field to explode.
The storms seemed to develop on a slight shear line, and we soon decided to drop south to intercept the most tasty storm on radar. By this point, a good number of thunderstorms had developed in a quasi-linear fashion close to I-70, and a several had become severe-warned. We ended up just to the south of Oaklay, where we parked up on a dirt track and had an awesome view of mammatus developing from the anvil of the storm. We sat in the same spot for about 30 minutes, watching the mamatus in an ever-changing cloudscape which saw the storm's outflow track steadily towards us from the west.
Super-res reflectivity and velocity for the storms developing in NW Kansas. I-70 runs through the middle of the images. Tilt 1. Credit: Radarscope.
Some of the mammatus we saw. This photo had extra definition already added, as it was taken through the tinted glass roof of the car.
However, our time watching this storm was limited - the storm was outflow dominated, and so strong straight-line winds could soon be seen racing towards us over the fields. The downdraft was made clear by the dust it blew from the dry fields - looking similar to a haboob. We turned our cameras to the dust and wind racing straight towards us, when in the distance, we were fortunate enough to witness a gustnado spin up in the outflow. It must have been about a mile away, alough was clearly visible as it kicked-up a significant quantity of dust and dirt, and crossed a main road. This was something that none of us had ever seen before, and so it felt like a small win for us. 
Super-res reflectivity and velocity images of the storms as they became increasingly outflow dominated. The line of dust being kicked up by the outflow between Oakley and Scott City was heading straight towards us at the time. Tilt 1. Credit: Radarscope.
Blurry image of the gustnado - taken on a shaky 300mm lens - it was getting windy as the gust front approached.
The gust front and outflow was soon upon us after the above photo was taken. We rushed to get inside the car as 40-50mph winds and blowing dust slammed us. A scary episode ensued when the car boot wouldn’t close properly, and we attempted to shut it - three times - while we wondered if we would be unlucky enough to be hit by another gustnado. In the kerfuffel, my hat was blown into a field - which I hastily ran after before it was blown into oblivion - and then my watch strap broke as I tried to agressively slam the boot shut. Thankfully, we eventually managed to get it shut. Although this was nowhere near funny at the time, this is now something we can look back and laugh at, and the whole episode has been immortalised with a short video created by Ben.​
The storm then merged into a quasi-linear line, which developed into an impressive mesoscale convective vortex on radar. We raced east, to get back ahead of the storm, as a linear shelf cloud developed on its leading edge. This shelf was very photogenic, especially so as, with the disk of the Sun visible through the storm's base, cloud-to-ground lightning strikes were being kicked out too. We had two excellent photo opportunities before it got dark, as we allowed the storm to catch up to us before racing ahead and then stopping for a second time. 

The finale of the day came just to the south of Hays, Kansas, where we watched the shelf pass right over us in full darkness. The lightning show was impressive, with almost constant cloud-to-cloud lightning and lots of cloud-to-ground lightning too. Unfortunately I have no pics, as I couldn't get my camera to focus properly!

Shelf cloud 1.
The Sun setting behind the shelf cloud - with a bonus lightning strike too.
Shelf cloud 3.