Risk of Elevated Thunderstorms - Sunday 9th May

Written on: 08th May 2021

This weekend there is the potential that we may see a few imported elevated thunderstorms track from mainland Europe towards the UK. 

Looking at the Met Office MSLP chart we see a deep area of low pressure just off the coast of Ireland with high pressure across Eastern Europe. This area of high pressure effectively causes the low pressure in the Atlantic to stall, whilst sending a number of weather fronts across the UK. 

This setup with low pressure to the west and high pressure to the east results in a warm southerly flow spreading across the UK and mainland Europe, with cold air moving eastwards overriding this region of warm air at the surface. This results in large instability build-up and combined with strong vertical wind shear (the change of wind speed and direction with height) can lead to nasty thunderstorms developing, with the potential to upscale into a mesoscale convective system (MCS). 

During Sunday we see this low pressure system trying to edge eastwards, confining the warm air to the far SE of the UK with the warmest weather across France. The cold front across the UK marks this boundary between the cool and warm air and the positioning of this front is crucial to where we may see thunderstorms develop.

Large instability begins to build during Sunday across parts of Northern France, with CAPE values approaching 1,000J/kg and this will lead to a few active thunderstorms breaking out across France during mid-afternoon. As we head into the evening, these thunderstorms will increasingly become elevated and will quickly become organised due to strong vertical wind shear (40knts). Unfortunately the low pressure appears to nudge eastwards through the day so it is likely that any thundery activity will be confined to mainland Europe, but there is a small risk that parts of the SE, with Kent in particular, may experience a few elevated thunderstorms. Many of the forecast models currently have storms breaking out and moving into the SE of England late on Sunday, but from experience models often overestimate the westward extent of elevated thunderstorms for our region so there is large uncertainty involved with the timing and location of any storms. Should Sunday play out as forecast, then the conditions will be favourable for thunderstorms to upscale into an MCS with the potential of producing flash flooding, large hail and frequent lightning. 

The charts below show the differences in the forecast models for Sunday evening showing the large uncertainty surrounding these thunderstorms, however if you are situated across Kent and Sussex you may get a lucky surprise. A convective forecast is likely to be issued on Sunday morning highlighting any risk areas involved. Hope you all have a great weekend!

Written By: Ben Sainsbury