Roads were blocked and cars were abandoned in the heavy downpours on Wednesday, just days before the city welcomes world leaders to the UN annual climate change summit.
Residents told of becoming stranded up to their knees in water, while speed limits were imposed on trains and motorists queued on Great Western Road.
Some areas of southern Scotland saw almost 80m of rainfall, according to the Scottish Environment Protection Agency.
“There was nothing for it but to accept it and get wet,” one person said on Twitter.
“When I stepped off of the pavement into the road, the rain water hit my knees. Haven’t seen floods like those here in years.”
Another person said: “Welcome to cloudburst Glasgow, eve of COP26.
One the eve of #cop26 flash floods after intense rain ☔️ creates chaos - cloudburst roads - shocking but sadly unsurprising that @RishiSunak has cut ✈️ fuel duty! Now is the time to act @BorisJohnson #notthisfuture @UofGGES @AdaptationScot @JustinTrudeau @JoeBiden @BBCBreaking pic.twitter.com/xKnDB9spyC
— Larissa Naylor (@biogeomorph) October 27, 2021
“A major artery closed due to pluvial flooding, night shift can’t get to the hospital, cars abandoned, no police so prof by day traffic Marshall by night.”
On Wednesday, a dozen flood warnings were in place as rain hit Scotland south from Glasgow to the border.
Some 25 flood warnings and alerts are now in place, including one at Pollok Country Park where the River Clyde passes through Glasgow city centre, and one in Edinburgh.
Most others were dotted throughout the Borders including Eskdalemuir Observatory, Dumfries and Galloway.
An amber warning for heavy rain also applies in the Lake District until just before midnight on Thursday.
Spells of sustained rainfall are expected further south throughout the day, with a yellow warning issued for heavy rain to spread across south-east Wales before clearing to the east through Friday, the Met Office said.
More rain is expected throughout the weekend with heavy widespread rain developing on Sunday when COP26 is set to begin.
Monday will see occasional downpours along with chilly, northwesterly winds, according to forecasters.
Pascal Lardet, flood duty manager for Sepa, said: “River and surface water flooding is likely, particularly in eastern Dumfries & Galloway and western Scottish Borders.
“There could be localised flooding to low-lying land and roads, disruption to travel and flooding in parts of communities. We are monitoring the situation closely with partners in areas such as Hawick, Newcastleton and Langholm.”