Gloucestershire 76 and 63 for 8 (C Overton 4-25, Davey 4-25) trail Somerset 237 and 223 for 1 declared by 322 runs
Craig Overton and Josh Davey continued to wreak havoc with Gloucestershire's batting as Somerset were defied by the weather on the third day of the Bob Willis Trophy match at Taunton.
What little play there was saw the visitors stumble from 14 for 3 at the start of play to 63 for 8, chasing an unlikely 385 to win.
Overton and Davey ended the day with identical figures of four for 25 and their team were clearly unhappy when umpires Ian Blackwell and Paul Baldwin deemed the light too pour to continue with a possible five overs remaining.
While the Gloucestershire batsmen made for the sanctuary of the pavilion, Somerset's fielders remained on the outfield and head coach Jason Kerr stood in lengthy conversation with the umpires. Clearly concerned that more rain is forecast tomorrow, Kerr and his players were desperate to complete victory, having been denied an almost certain win by the elements in their previous group match against Warwickshire.
Heavy overnight rain followed by showers meant no play before tea. When the players finally emerged from the dressing rooms at 4pm, Somerset had a potential 39.4 overs to clinch victory with a day to spare.
But at 5.25pm the rain returned, with Gloucestershire 61 for six, and a further ten overs were lost. When play restarted at 6.05pm, only eight remained in the day. With three of them bowled and with the floodlights on, the umpires made the ruling on the light to complete a day of intense frustration for Somerset.
Craig Overton had made the first breakthrough of the day, comprehensively beating George Hankins' defensive shot and uprooting two of his stumps in the first full over to make the score 23 for 4.
Ryan Higgins confidently off-drove his first delivery for four and then top-edged a six over third-man off Overton, but soon it was 49 for five as Graeme van Buuren's loose shot saw him caught behind off Davey.
Gareth Roderick failed to trouble the scorers, carelessly chipping a catch to Eddie Byrom at mid-wicket off Davey and at 49 for six, a three-day finish looked in prospect.
But the former Middlesex pairing of Higgins and George Scott survived for eight overs as Jamie Overton and Jack Brooks took up the attack.
After 40 minutes more were lost to rain, Craig Overton struck with the sixth delivery of the resumption, pinning Higgins lbw for 21.
But soon the light was not considered good enough to continue and Somerset will be praying overnight that there is sufficient play tomorrow to complete a dominant performance.