Middlesex 410 (Stirling 138, Robson 107) and 125 for 4 (Gubbins 38) drew with Glamorgan 288 (Lloyd 59, Labuschagne 51, Cullen 50, Finn 5-75)
Rain washed away hopes of a final-day run chase at Radlett as Middlesex and Glamorgan were forced to settle for a draw.
Middlesex, who held a 247-run advantage when play was halted with 58 overs scheduled to be bowled, appeared to be toying with the idea of setting their visitors a target.
But the bad weather that had already disrupted days one and three returned to dispel any possibility of a positive outcome to the inaugural County Championship fixture at Cobden Hill.
The draw leaves Middlesex with just one victory from their first seven Championship games, while Glamorgan remain undefeated this season and will go into the second half of the campaign occupying a promotion spot.
The initial target for the Welshmen, resuming at 274 for 9 in the morning, was to try and snatch an additional batting bonus point by hitting the 300 mark.
They fell 12 runs short despite the efforts of Graham Wagg, who eventually perished for 48 as he heaved a Tom Helm bouncer into the hands of Nick Gubbins, running in from the boundary.
However, Middlesex appeared reluctant to force the pace and build on their 122-run lead at the start of their second innings, with tight bowling by Marchant de Lange and Lukas Carey restricting them to only two boundaries in the first 15 overs.
Timm Van der Gugten made the breakthrough for the visitors, with Marnus Labuschagne snapping up Stevie Eskinazi at point, while opening partner Sam Robson hit 36 before he fell to Charlie Hemphrey's superbly-judged catch in the deep.
Gubbins did appear keen to accelerate proceedings, blazing four fours and a six in his breezy knock of 38 before he departed lbw, attempting to reverse-sweep Labuschagne, who took 2 for 25.
Dawid Malan followed that up with 18 from as many deliveries, but he was caught behind off de Lange for the second time in the match as the home side struggled to gain traction.
Paul Stirling and George Scott advanced the Middlesex total to 125 for 4 from 33 overs before light drizzle developed into heavier rain and the players left the field at 2.15pm.
Umpires Graham Lloyd and Neil Bainton eventually abandoned the contest at 4pm, with Middlesex taking 12 points to Glamorgan's nine.
