Flooding and travel disruption is likely in places, with significant snow expected across higher ground in some northern areas.
The Met Office has issued an amber alert for heavy rain in southwest England on Monday and Tuesday.
The region could see 30 to 50mm of rainfall and 60 to 80mm on higher ground, especially in south Dartmoor, increasing the risk of flooding in already saturated areas, the Met Office said.
There are also yellow alert rain warnings in place for more of England - including London, the South East and the South West - and parts of Wales and Northern Ireland on Monday.
Tuesday will bring more bad weather across the UK as Storm Chandra intensifies, with a patchwork of weather warnings blanketing much of the country.
An amber warning for wind has been issued for Northern Ireland on Tuesday, bringing gusts of 60 to 70 mph, reaching 75 mph in some coastal locations, the Met Office said.
Chief forecaster Paul Gundersen said the UK was facing a "complex spell of weather" as a deep area of low pressure moved in, and urged people to stay up to date with weather warnings.
"Initially strong winds will impact the Isles of Scilly, western Cornwall and southwest Wales which are still vulnerable after Storm Goretti, gusts of 70 to 80mph are possible here," he said.
"Heavy rain is an additional hazard as it falls on saturated ground in Dorset and southern parts of Devon, Somerset and Cornwall.
"As Chandra interacts with colder air further north snow becomes a hazard, with 10 to 20cm of snow possibly accumulating over higher ground in the Pennines, southern Scotland and the Highlands."
Yellow alerts are also in place for rain and snow in parts of Scotland, the Midlands, the North East and North West of England and Yorkshire on Tuesday.
Rain will turn to snow on higher ground, with 2 to 5cm falling in places above 300m elevation and 10 to 20cm falling above 500m.
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The Met Office is warning of flooding, transport delays and cancellations, power cuts and landslides.
Some communities face the possibility of being cut off by flooded roads.
Storm Chandra arrives just days after Storm Ingrid battered parts of England's southwest on Friday and Saturday.
Earlier in the month, Storm Goretti brought snow, rain and strong winds to much of the UK.
The weather system has been dubbed Storm Chandra because it is the next name on the list shared between the UK, Ireland and the Netherlands. Under the alphabetical list, the storm that comes afterwards will be named David.
Other recent storms were named by overseas naming centres, with Storm Goretti being named by weather service Meteo France and Portuguese authorities naming Storm Ingrid.
The Israel Defence Forces (IDF) said in a statement it had retrieved the body of police officer Ran Gvili and that his family had been informed.
Identification of the remains was confirmed by the National Institute of Forensic Medicine, in cooperation with the Israeli police, and the military rabbinate, the IDF said.
Mr Gvili, 24, was a sergeant first class in the Israeli police special forces, who was killed at the Alumim kibbutz during the October 7 attacks in 2023, before his body was taken to Gaza.
The announcement that his remains had been found and identified came a day after Israel's government said the military was conducting a "large-scale operation" in a northern Gaza cemetery to locate them.
The discovery of his remains marks the return of the last remaining hostage held in Gaza, fulfilling a key condition of the first phase of Donald Trump's peace plan.
Mr Gvili's family had urged Israeli Prime Minister Benjamin Netanyahu not to enter the second phase of the plan until his remains were recovered.
Now Mr Netanyahu has hailed the return of Mr Gvili as "an incredible achievement", adding that "I promised we would bring everyone home and we have brought everyone home".
Hamas, the Palestinian militant group that has governed Gaza, emphasised its compliance with the peace deal.
Spokesperson Hazem Qassem said: "The discovery of the body of the last Israeli prisoner in Gaza confirms Hamas's commitment to all the requirements of the ceasefire agreement on the Gaza Strip, including the prisoner exchange process and its complete closure as stipulated in the agreement.
"The movement will continue to adhere to all aspects of the agreement, including facilitating the work of the National Committee for the Administration of Gaza and ensuring its success.
"We call on the mediators and the United States to compel the occupation to cease its violations of the agreement and implement its required obligations."
Ahead of the discovery, an Israeli military official revealed there were "several intelligence leads" regarding the possible location of the police officer's remains.
A "targeted operation" was under way in northern Gaza, they added.
Mr Netanyahu's office said on Sunday that, once the search was done, Israel would open the Rafah crossing between Gaza and Egypt.
But a government spokesperson gave no immediate answer when asked when the border crossing would now reopen.
Israel has repeatedly accused Hamas of dragging its feet in the recovery of the final hostage, but the group said it had provided all the information it had about Mr Gvili's remains.
Mr Gvili's body will now be returned to his family for burial.
Some 1,200 people were killed in the Hamas-led October 7 attacks, with a further 251 taken hostage.
At least 180 million people in 37 states - more than half America's population - are affected, according to the National Weather Service (NWS).
Seventeen states and the District of Columbia have declared an emergency, with rescue teams and supplies on standby.
The number of deaths attributed to the storm now stands at 15, officials said.
There were three fatalities in Pennsylvania, three in Tennessee, two in Louisiana, two in Texas, two in Mississippi, one in Kansas, one in Massachusetts and one in Arkansas, Sky's US partner network NBC News reported.
Temperatures plunged to -20C in Texas, while in New Mexico, residents were deluged by 31 inches (78cm) of snow.
"This storm is exiting the East Coast now, with some lingering snow squalls," said Allison Santorelli, a meteorologist with the NWS's Weather Prediction Centre.
"But the big picture story is the extreme cold, it's lasting into early February."
There were widespread power outages across the US, with 813,498 homes without power just before 11am eastern time on Monday (4pm UK time), according to PowerOutage.us.
Tennessee was the worst-hit state with 250,203 outages reported, followed by Mississippi with 160,751 and Louisiana with 126,207.
Josh Weiss, from the National Oceanic and Atmospheric Administration, said the storm was "unique" due to its broad spread - covering 2,000 miles - and the extreme cold it's forecast to bring over the next week.
More than 14,500 flights were cancelled on Sunday and another 5,500 delayed, according to tracking website FlightAware, making it the worst day for flight cancellations in the US since COVID, aviation analytics firm Cirium claimed.
There were more than 6,400 flight delays and cancellations nationwide on Monday, according to flightaware.com.
Homeland Security secretary Kristi Noem urged people to "stay home" due to "very, very cold" temperatures.
Thousands of bin lorries have been fitted with snow ploughs in New York City, said mayor Zohran Mamdani, who warned of the coldest temperatures for eight years.
In Central Park, where some people used skis to get around, 28cm of snow were reported on Monday.
Students in America's biggest city have been told that Monday will be a remote learning day.
Similar orders are in force in other storm-affected states.
"An Arctic siege has taken over our state," said New York governor Kathy Hochul. "It is brutal, it is bone-chilling and it is dangerous."
New York communities near the Canadian border have already seen record-breaking lows, including -45C (-49F) in Copenhagen, a village in Lewis County.
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Mikie Sherrill, the governor of New Jersey, announced a 35mph speed limit on highways and said she was expecting conditions the "likes of which we haven't seen in years".
In Georgia, senior state meteorologist Will Lanxton said it was "perhaps the biggest ice storm we have expected in more than a decade".
From 2021 to 2023, the country was considered to have "eliminated" the disease, but global health officials say measles transmission was re-established in the UK in 2024.
Vaccination coverage has flatlined in recent years, with recorded measles infections in the UK soaring to 3,681 in 2024.
Spain, Austria, Armenia, Azerbaijan and Uzbekistan also lost their status, and the WHO urged countries to boost vaccination rates to prevent the disease infecting more children.
"It is unsurprising the UK has lost its WHO measles elimination status, following nationwide outbreaks since 2024 and the preventable death of a child in 2025," said Dr Ben Kasstan-Dabush, assistant professor of global health at the London School of Hygiene and Tropical Medicine.
The latest figures for England from the UK Health Security Agency (UKHSA) show that in 2024-25, just 83.7% of five-year-olds had received both MMR (measles, mumps and rubella) vaccine doses, down year-on-year from 83.9%.
This was the lowest level since 2009-10.
Also in 2024-25, some 91.9% of five-year-olds had received one dose of the MMR vaccine, unchanged from 2023-24 and the lowest level since 2010-11.
The WHO advises that at least 95% of children should receive vaccine doses for each illness to achieve herd immunity.
"Infections can return quickly when childhood vaccine uptake falls," said Dr Vanessa Saliba, consultant epidemiologist at the UKHSA.
"Measles elimination is only possible if all eligible children receive two MMRV doses before school.
"Older children and adults who missed vaccination must be caught up."
From the start of January, children have been offered a combined MMRV vaccine, which protects against measles, mumps, rubella and chickenpox, instead of the MMR jab, as part of the childhood routine two-dose vaccination schedule.
Dose one is being offered at one year of age and dose two has been brought forward from three years four months to a new 18-month appointment.
The rollout across the four nations of the UK comes after the combined MMRV (measles, mumps, rubella and varicella) jab was recommended by the Joint Committee on Vaccination and Immunisation (JCVI) in 2023.
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A WHO spokesperson said the UK's change of status "reflects a broader challenge" that the organisation is facing across Europe.
"Outbreaks of measles and other vaccine-preventable diseases are threats to health security in Europe," they added.
Dr Bharat Pankhania, senior clinical lecturer in public health medicine at the University of Exeter Medical School, said: "It's extremely concerning that in the UK we now have pockets of low or no vaccine uptake."
He warned that "we urgently need to remedy this situation".
Sky News understands that insolvency practitioners from Kroll were formally appointed as administrators to Claire's UK and Ireland earlier on Monday.
It comes three weeks after Sky News revealed that the chain's owner, Modella Capital, filed a notice of intention to appoint administrators to both Claire's and TOFS, the discount retailer it also acquired last year.
In a statement on Monday evening, Kroll said: "Philip Dakin, Benjamin Wiles and Janet Burt of Kroll Advisory Ltd were appointed as joint administrators of CAUKI Ltd on 26 January 2026.
"The company is continuing to trade during this period."
Modella bought the company last September, several months after Claire's had filed for insolvency in both the US and the UK.
Retail analysts are sceptical that a buyer will emerge for many of the remaining 156 Claire's stores in Britain and Ireland.
Sources close to the situation said earlier this month that a combination of government policy - with a significantly increased tax burden placed on the retail industry - and demands from landlords to take back swathes of Claires' shops, had rendered the future of the chain unviable.
The retail industry continues to face significant headwinds, with chains including Poundland having closed significant numbers of shops.
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Modella also owns businesses including WH Smith's historic high street estate, which it has rebranded as TG Jones, as well as Hobbycraft.
Claire's had previously traded from nearly 300 shops in the UK, but has been hit by changes in consumer behaviour among its traditional teenage customer base.
Significant numbers of jobs were lost in restructuring processes prior to Modella's purchase of the business.