Snow and sub-zero temperatures could arrive in Derry and the rest of the North sooner than originally thought according to the Met Office.
Last week the Met Office said there was an "enhanced risk of snow" for the North towards the end of January and the beginning of February.
However, an update on Met Office website on Monday afternoon suggests that snow could arrive as soon as Saturday.
"Outbreaks of rain, sleet and some snow are likely to move slowly south and eastwards on Saturday, but tending to become lighter and more patchy as it does so," said the Met Office.
"Sunday looks generally quiet, with a good deal of dry and bright weather. Thereafter, it looks set to remain mainly on the cold side, but also unsettled and sometimes windy, with gales possible in the north.
"Any milder spells will tend to be brief, and associated with longer spells of rain.
"The rain could turn to snow at times, particularly across northern, central and eastern areas, especially later in this period.
"Some drier, brighter spells are likely, perhaps with snow showers, during such spells, frost could become widespread and severe."