Thunderstorms and llightning hit St Albans overnight but the heatwave is set to continue today with temperatures reaching 25C.
Firefighters attended seven incidents in St Albans and Watford, and the powerful line of storms left many without power.
A lightning strike on the rail tracks in St Albans is currently disrupting Thameslink train services between Luton and London St Pancras.
Readers have been sending in pictures of the severe weather.
Liz Needham took the picture below from the seventh floor of Telford Court at around midnight.
In Chiswell Green, Mark Coltman took a video of a lightning strike. He said: “Just before midnight we could feel a deep rumbling followed dull flashes.
“We could tell it wasn't close as we counted the seconds in between.
“Then around midnight it was as if Thor himself was having a night out in Batchwood, the whole house lit up and when the thunder hit almost immediately afterwards we knew it was almost on top of us.
“Needless to say both our boys were now fully awake and downstairs. At around one o'clock I tried to herd them back to bed but it was like herding frightened cats.
“As the youngest was at the top of the stairs the whole house seemed to 'crack' and lit up like a flashbomb.
“My wife and eldest were downstairs and felt an electrical jolt through them, the whole house smelt of ozone, just like being at the beach.
“The lights flicker then came back on, the only casualty seemed to be the wifi hub that glowed a dull orange at the front and then died.
“We got to bed about 2 o'clock, eventually.”
Below is Mr Coltman's video.
In Harpenden, Felicity Scriven took the picture below in Stonemason Close.
The property photographer at Hawk & Chadwick also caught the lightning (below).
Despite the turbulent weather last night, much of the county has woken up to rather pleasant conditions today.
Below is a collection of reaction from social media.
Hi anyone else out there in St Albans still awake. Unbelievable storm here- not forecast. Electricity gone off. Car alarms going off
— Katherine Thorogood (@KathCanary) July 3, 2015
I have never driven through a storm like that!! St. Albans is having large down here!
— ILL PHIL (@ILLPHIL85) July 3, 2015
That was the maddest thunderstorm I can remember - purple flashes so bright hurt my eyes #stalbans
— anderew (@anderew) July 3, 2015
I think the world is coming to an end in St Albans. Lightning every few seconds and the loudest thunder I've ever heard!
— Kate Pankhurst (@ktpanks) July 3, 2015
I'm guessing everyone in @StAlbansDNews is awake now then... #thunder #StAlbans
— MrJago (@thisisjago) July 3, 2015
I'm guessing everyone in @StAlbansDNews is awake now then... #thunder #StAlbans
— MrJago (@thisisjago) July 3, 2015
Did you get any pictures or video of the storm? Email charlotte.ikonen@london.newsquest.co.uk
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here