Snowstorms could delay the extradition of wanted Briton Neil Entwistle to the US until the middle of this week.
Entwistle, 27, is waiting to be extradited to face trial for the murder of his wife, Rachel, a former teacher at a Worcestershire school, and nine-month-old baby daughter.
But Paul Dunne, assistant chief deputy for the Boston marshals office, which is responsible for escorting him back, said weather could cause a delay.
He told the Boston Globe marshals were unlikely to fly to England until later this week because of a snowstorm expected this weekend in the north-eastern United States.
He said Entwistle would probably return to Massachusetts by mid-week.
A PA WeatherCentre fore-caster said up to 38cm (15 inches) of snow could fall in Massachusetts over the weekend.
He said a band of heavy snow was moving into the area and temperatures would not rise above freezing until mid-week.
A British Home Office minister signed a surrender warrant on Friday that cleared the US Marshals Service to bring Entwistle back to Massachusetts.
Entwistle agreed to be extradited to the US "as soon as possible" when he appeared at Bow Street Magistrates Court.
His solicitor, Judith Seddon, said: "He believes he will receive a fair and proper hearing in the US on these very serious allegations."
Entwistle, formerly of Worksop, Notts, was arrested at Royal Oak Tube station in west London on Thursday over the murder of his American wife, who was a teacher at St Augustine's Catholic High School in Redditch until last year, and baby Lillian.
Their bodies were discovered by police at the family home in Hopkinton, Massachusetts, on January 22. Entwistle had flown to the UK the day before.
They were killed with bullets from a .22-calibre handgun which, according to a police affidavit, belonged to Mrs Entwistle's father.
Unemployed computer programmer Neil has told police he did not kill them, but found them shot dead when he returned from an errand.