The warnings precede a 10-day scorcher that kicks off this weekend and lasts through mid-July.
Temperatures are set to skyrocket in the coming days as forecasters warn that continued, extreme heat will push Britain into heat wave territory.
As the highways soften, gritting trucks may be brought out to scour the roads — a phenomenon more common in the depths of winter.
RAC spokesman Rod Dennis said: “As the weather warms up, so will the roads, and you can pretty much guarantee that the road temperature will be significantly higher than the air temperature, especially where the sun is shining.
“The heat can lead to some softening of the road surface – blacker areas of asphalt is the tell-tale sign.
“If temperatures really skyrocket, it may also be necessary to deploy litter trucks, as salt can help improve vehicle grip on slush roads.”
Weather models reveal ground temperatures under blazing sunshine reaching 40C by mid next week.
Air temperatures, which are more commonly used in weather forecasting, can exceed 30°C before the middle of the month.
James Madden, Exacta Weather forecaster, said: “We are experiencing an ongoing period of very warm weather from the weekend to the middle of the month.
“This could push temperatures to 30°C, with maximums of 35°C now possible in some isolated spots.
“This is an important period of warm weather and the country could be facing a major heat wave.”
Rising temperatures caused weather models to collapse over the weekend, predicting air temperatures of 40C.
Contrary to extremely high ground temperatures, 40C has never been recorded during a summer in the UK and is ‘highly unlikely’ next week.
John Hammond, meteorologist for Weather Trending, said: “One or two computer models will indicate temperatures of up to 40C in the next week or two.
“That would be unprecedented, but highly unlikely.”
The mercury will skyrocket from today, reaching the mid-to-high 20°C by the end of the week and as high as 30°C by the end of the week, he warned.
He said: “After the middle of the week with more extended sunshine and light winds, temperatures will climb quite a bit to mid to high 20Cs in southern and eastern areas and by the weekend, not far from 30C.
“It will probably be the southernmost areas that will see the peak of the heat and this will be especially around coastal areas where there will be less cloud cover.”
“It is the south and east that will see the highest temperatures later this week.”
“Next week the heat will continue and the high pressure will dominate and I don’t see many signs of significant rain in the coming days.”
Scotland and northern England are likely to remain cooler in a northwesterly wind and may see some rain, he added.
Drought fears amid forecasts of no rain in parts of the UK have sparked fears of a garden hose ban and water shortages.
Officials have urged Britons to use water wisely while showering rather than bathing and using washing machines sparingly.
Jim Dale, a meteorologist for British Weather Services, said: “I see a period of 10 days to two weeks where parts of the country will have no rain at all.”
“This could be problematic as river levels drop and put these regions in a drought situation.”
The heat wave will be driven by a huge area of high-pressure buildup in the Atlantic and about to engulf Britain, he explained.
He said: “The Azores will start to stretch into Britain in the next few days and it’s the weekend that temperatures can really start to soar.
“This is the picture until about mid-month, and while we largely expect temperatures to reach the high -20°C, it wouldn’t be out of the question to reach 30°C.”
Bookmakers have lowered the odds of a series of warm weather odds, with Coral offering 1-2 on a hose ban and 4-5 of 2-1 on melting the 38.7C record.
Spokesperson John Hill said: “With temperatures steadily rising, we’ve reduced the chances of breaking the UK’s highest-ever temperature this month.
“It looks like we’re going to have a period of dry weather in the coming weeks, and as a result of that forecast, we now have a good chance for the UK to impose a garden hose ban this summer.”
Ladbrokes is offering 10-11 on temperatures for the next week, bringing home its hottest July ever.
Spokesperson Alex Apati said: “There is a good chance that this month will be the hottest July on record, if the last chances are just a little bit longer.”