A snow and ice warning for southern Scotland tonight has been issued by the Met Office.
It was followed by severe flood warnings for Inverurie and Kintore in Aberdeenshire, where “extensive flooding” of homes is expected.
The yellow - “be aware” - severe weather alert for snow will be in force from 7pm until 9am tomorrow.
It covers the Borders, Dumfries and Galloway, and parts of South Lanarkshire and East and South Ayrshire.
The snowfall will be mainly over 200m, but may to fall to lower levels for a time.
Roads above that level include stretches of the M74, A76, A68 and A7.
The Met Office said snow is also forecast above 200-300m in eastern Scotland, which could affect sections of the A90 north of Dundee and the A96 in Aberdeenshire.
More snow is likely across Scotland from Monday as conditions turn colder.
A Met Office spokeswoman said: “A zone of rain and hill snow will affect Northern Ireland later on Thursday evening before moving into parts of Scotland and northern England during the early hours of Friday.
“Over ground above 200 to 300 metres, snow is expected to accumulate, especially over Scotland where there is also a chance that snow could fall to lower levels for a time.
“As this rain and snow moves away, skies will clear allowing temperatures to drop and icy patches to form on untreated surfaces.
“Please be aware that rain, snow and icy patches could lead to some disruption to travel.
The two severe flood warnings from the Scottish Environment Protection Agency (Sepa) came as the Met Office updated its amber heavy rain warning for eastern Scotland with concern for “localised, high impacts”.
A further 37 flood warnings are in force for Aberdeenshire, Aberdeen, Moray, Perthshire and Angus.
Sepa said flooding in Inverurie from the River Don and River Urie was expected to include Port Elphinstone and the Old Canal areas.
A paper mill, waste water treatment works and the Aberdeen-Inverness railway line would also be “significantly affected”, and many roads left impassable.
The agency said river levels would “significantly exceed” those seen in 2002 and 2009 when they peak early tomorrow, with levels in the Urie “expected to be the highest in recent history”.
Threatened areas of Kintore, downstream on the Don, include Castle Hill and Kingsfield Road.
The Met Office’s amber warning, for Aberdeenshire, Angus, eastern Perthshire and Dundee, in force until 8am tomorrow, for 40-60mm of rain and more than 80mm over high ground.
Sepa hydrology duty manager Nigel Goody said: “The saturated conditions across Aberdeenshire, Tayside and Angus will mean there is a likelihood of significant flooding during Thursday and overnight into Friday.
“The prolonged heavy rain overnight and throughout today is causing river levels to rise again, with peak times expected to be late on Thursday night and early Friday morning.
“Particular concern today is focused on flood prone areas close to the River Don and River Deveron, which could potentially see severe flooding impacts.
“Other areas at risk of significant flooding impacts today include the River Isla, the lower Tay and Angus rivers.
“Significant flooding impacts are likely to be widespread across the north east in general with flooding expected to affect communities and cause disruption to infrastructure and travel.”
Major roads suffering flooding included the A96, which was closed between Kintore and Aberdeen, along with the A90 near Brechin. The A90 near Forfar and A9 near Blair Atholl were also badly affected.
The Aberdeen-Inverness railway line was closed and trains were also cancelled between Dundee and Aberdeen.