The Old Military Road at the Rest and Be Thankful will close to all traffic on Saturday as a safety precaution with heavy rain forecast for the region.
The road will remain open over Christmas Eve and Christmas Day before closing at 3.30pm on Boxing Day.
Traffic will be diverted via Tarbet and Inveraray using the A82, A85 and A819.
BEAR Scotland teams will complete patrols on the diversion route to assist with any issues and help keep traffic moving.
Assessments on the slopes above the A83 indicate that the hillside remains highly saturated as a result of recent weather, and with further persistent heavy rainfall expected on Boxing Day, the decision has been taken to close the road during the hours of darkness from December 26 to 27.
A safety assessment will take place on Sunday to consider the road’s re-opening.
Eddie Ross, BEAR Scotland’s North West Representative said: “A yellow warning has been issued for heavy rain on Boxing Day, with up to 50mm of rain forecast at the Rest and be Thankful over the course of the day.
“The rainfall expected will inundate what is already a highly saturated hillside; however, with further mitigation measures now in place to protect the OMR, and with engineers on site to monitor conditions, we anticipate being able to operate the local diversion route for a period of this weather warning.”
He continued: “Persistent rain is expected over a 24 hour period, presenting the first big test for the new mitigation measures installed on the hillside and adjacent to the OMR, and with this in mind we have taken the decision, with Transport Scotland, to close the OMR from 3.30pm on Saturday afternoon as a safety precaution during the hours of darkness.
“All traffic will be diverted from 3.30pm on Saturday using the standard diversion route between Tarbet and Inveraray, and Western Ferries will continue to operate their scheduled service.
“Teams will carry out a safety inspection from first light on Sunday 27 December to inform the decision to re-open the OMR to traffic.
“We understand the frustration that this causes, however it is essential that we continue to implement a safety-first approach and do everything we can to keep road users safe.
“We thank all road users and the local community for their patience while we address the ongoing situation at the Rest.”