The Met Office has predicted which parts of the UK will swelter in 40C temperatures in the next few days and pin-pointed the areas which will escape the blowtorch conditions.
A national emergency has been declared with a first ever red warning for exceptional heat next week.
Monday and Tuesday could smash records, which will in turn "lead to serious illness or danger to life".
But while he Met Office expects "population-wide" health effects, some areas will be cooler in comparison.
The Red Extreme heat national severe weather warning covers July 18 and 19 for parts of central, northern, eastern and south eastern England.
London is expected the be the warmest part of the UK, with the mercury predicted to burst through 40C in the capital.
Met Office maps show 38C heat on Tuesday across most of the east coast.
By lunchtime on the same day, temperatures in Birmingham will rise to 37c.
England's most cool area will be the south west, with highs of 27c forecast in Devon and Cornwall.
Northern parts of Scotland will be around half as hot as England's baking areas, with Aberdeen expecting a maximum of just 21C.
The north east of England will see 28C warmth on Monday afternoon before 32C heat arrives 24 hours later.
Unlike most places, south Wales will be milder on the Tuesday with Monday temperatures peaking at 35C.
Met Office Chief Meteorologist Paul Gundersen, said “Exceptional, perhaps record-breaking temperatures are likely early next week, quite widely across the red warning area on Monday, and focussed a little more east and north on Tuesday.
"Currently there is a 50% chance we could see temperatures top 40°C and 80% we will see a new maximum temperature reached.
“Nights are also likely to be exceptionally warm, especially in urban areas.
"This is likely to lead to widespread impacts on people and infrastructure.
"Therefore, it is important people plan for the heat and consider changing their routines.
"This level of heat can have adverse health effects.”
The Met Office added: "Temperatures are expected to start to return closer to normal for the time of year from the middle of next week onwards as cooler air pushes across the country from the west."
There is also a high risk of heat-sensitive systems and equipment overloading, potentially causing power loss to essential services such as water and mobile phone services, while speed limits are likely to be imposed on railways to protect tracks.
Check the Met Office forecast in your region here.
London & South East England
Cloud clears on Saturday morning to leave a fine, dry day with long sunny spells and light winds.
Feeling very warm inland, cooler around coasts. Maximum temperature 28C.
On Sunday it stays fine and dry with light winds. Things becoming very hot by Monday, perhaps exceptionally hot on Tuesday.
West Midlands
This weekend will be dry with prolonged intervals of strong sunshine, though some higher-based cloud making the sunshine hazy at times.
Feeling warm with temperatures up compared to Friday. Maximum temperature 26 °C.
Becoming extremely hot by Monday, with exceptionally warm nights as well.
North West
It will be dry with prolonged intervals of strong sunshine this weekend, though some higher-based cloud making the sunshine hazy at times.
Feeling warm with temperatures up compared to Friday. Maximum temperatures of 24C are expected.
Largely dry with sunny intervals, with Monday and Tuesday becoming extremely hot by day - and exceptionally warm nights as well.
North East
Saturday will see a fine, dry day with long sunny spells and light winds, cloud amounts increasing towards the evening.
But rain is possible early on Sunday. Otherwise, staying fine and dry with light winds.
Becoming hot by Monday, and very hot Tuesday, with very warm nights. Breeze increasing by Tuesday.
South West
Another dry day to come on Saturday with lots of sunshine throughout, although this becoming rather hazy at times.
Temperatures starting to rise. Maximum temperature 27 °C.
It will again but sunny on Sunday and Monday and becoming very hot by day, especially further east, with exceptionally warm nights as well. A risk of thunderstorms by Tuesday in the far west.
Wales
It is another predominantly dry day on Saturday with lots of sunshine throughout, although this becoming hazy at times. Maximum temperature 27 °C.
Sunny on Sunday and Monday and becoming very hot by day, especially further east, with exceptionally warm nights as well.
A risk of thunderstorms in the southwest is reported by Tuesday.
Scotland
Dry with plenty of warm sunshine for many, very warm in the south on Saturday. Cloudier across northern and western Scotland with bursts of rain at times.
The outlook is mostly dry and increasingly sunny from Sunday through to Tuesday.
Afternoon highest lifting day by day, particularly across southern areas.
Northern Ireland
Generally dry with a mix of sunny spells and high cloud on Saturday. Temperatures lifting into low 20's again for many.
However some showers later into the weekend, mainly around the north coast. Maximum temperature 22 °C.
Afternoon highest lifting day by day, particularly across southern and eastern areas, with some chance of breaking the all time temperature record on Tuesday.
