The yellow weather warning for rain came into force at midnight on Thursday and is set to lift at midday on Saturday.
It covers Central, Tayside, Fife, Strathclyde, Highlands and Eilean Siar, and predicted widespread heavy rain falling from Wednesday, right through until Saturday daytime.
Warnings of floods and damage to buildings, as well dangerous driving conditions and delays have been issued by the forecaster.
Despite the heavy rainfall expected in the west, the next few days are going to be uncharacteristically warm for this time of year.
In the Lothians and Dumfries and Galloway, Friday could reach a maximum temperature of 19 degrees. Occasional rain is forecast but it is expected to be largely dry and sunny in the afternoon.
Fort William is covered by the warning and will see almost constant rain today. Temperatures are expected to reach 16 degrees at 9am, and are forecast to hover there until 9pm.
Glasgow and Strathclyde will see some patchy rain, though it will be heavy across Argyll. Longer dry spells will be seen in the afternoon developing from Glasgow and moving south eastwards. A high of 16 degrees is expected in the afternoon.
Tomorrow will be a bright start in the east but cloud and rain in the west will spread across the country during the morning. The rain is expected to ease in the afternoon, as the yellow weather warning lifts but it will remain a dull, drizzly day for most.