Stuart Broad and James Anderson on opposite sides as Notts bowl out Lancashire for 214.
Surrey's Gus Atkinson takes 6-68 - his first five-for - for 2022 champions against Essex.
Second-placed Hampshire all out for 229 on day one against Warwickshire.
Australia batter Steve Smith makes debut for Sussex at New Road
Jonny Bairstow takes three catches behind stumps for Yorkshire against Glamorgan.
On-loan paceman Henry Brookes takes 6-20 on debut for Derbyshire.
Somerset v Northamptonshire 137-4
What a shame, especially given this was forecast as the best day of the week.
Somerset had clawed themselves back into the match in the 37.4 overs possible but the weather has ended the day early.
Ricardo Vasconcelos made an eye-catching 70 before becoming the first of Lewis Gregory's two scalps.
Fingers crossed tomorrow is better.
Derbys 102-0 v Leics 122
Haider Ali pulls a ball from Chris Wright. He doesn't time it perfectly but three runs takes him to a 59-ball half-century and brings up a 100 partnership with Harry Came.
That will make Haider feel a whole lot better after a disappointing start to his stint at Derby.
Essex 224-6 v Surrey
Since dropping Alastair Cook twice, Surrey's fielding has been outstanding.
Ben Foakes gleefully grabs his third catch of the innings as Michael Pepper attempts a reverse sweep - a poor choice of shot in the circumstances.
Doug Bracewell toddles out to join Simon Harmer. Three wickets gone for 20 runs since tea.
Notts 46-2 v Lancashire 214 - tea
Dave Bracegirdle
BBC Radio Nottingham
Brett Hutton, Josh Bohannon and Tom Bailey have been the stand-out performers after the first two engrossing sessions at Trent Bridge.
Hutton, playing his 50th first class match for Notts, bagged the 13th five-wicket haul of his career in taking 5-66, helping by some outstanding catching from his team-mates.
Bohannon’s 68 kept the home side at bay, until he was bowled by a beauty from Hutton that just nipped back to clip the stumps.
That left Bailey to apply a little long handle at the back end of the Red Rose innings and he twice cleared the ropes in a lusty cameo of 48 not out.
After whipping off his pads, Bailey nipped out both left-handed Bens, Duckett and Slater, to leave the contest on an even keel at tea.
Worcs 264 v Sussex 23-0
Ben Gibbon comes up for a new over and his first delivery is punched to the mid-on boundary by Ali Orr.
Worcestershire will be hoping for a couple of early wickets to put a doubt in the minds of the batters to come - including Australia's Steve Smith.
Hampshire 229 v Warwickshire 0-0
Alex Davies and Rob Yates stride out to begin the Warwickshire reply at the Ageas.
Mohammad Abbas, the leading wicket-taker in Division One, will take the new ball.
Essex 224-5 v Surrey
A big partnership ended with the wicket of Matt Critchley, Surrey also send his partner on his way as Jordan Clark strikes.
Tom Westley drives but doesn't get his foot to the pitch of the ball and a thin inside edge drags it back into his stumps.
Simon Harmer is the new batter for the home side.
Essex 224-4 v Surrey
Michael Pepper has a look at a couple from Will Jacks then launches the next over long-on for six. Quite a way to get off the mark.
Notts 46-2 v Lancashire 214
Image source, Getty ImagesWickets aplenty on an entertaining first day at Trent Bridge.
Brett Hutton's five wickets limited Lancashire, with only some late hitting from Tom Bailey getting the visitors to 214.
Bailey then took two wickets with the new ball, including England opener Ben Duckett clean bowled, to leave this one delicately poised at the tea interval.
Essex 218-4 v Surrey
We saw a brilliant catch by Ben Foakes during the morning session, but how about that by Rory Burns?
Matt Critchley drives at a floated delivery by Will Jacks and Burns somehow clings onto a flying right-handed chance at slip.
Critchley hit two sixes and six fours in his 104-ball innings and put on 114 with Tom Westley, who has been joined by Michael Pepper.
Quote MessageJust watch the reaction of Jamie Smith at short leg, he can't believe that Rory Burns has come up with that. It was behind him and his right hand as well."
BBC Radio London's Mark Church
Yorskhire v Glamorgan 215-8 - tea
Jonathan Doidge
BBC Radio Leeds commentator
Having witnessed a Glamorgan fightback in the back half of the opening session, the afternoon was very much Yorkshire’s.
The hosts struck as early as the third ball of the afternoon, when Mickey Edwards had Sam Northeast caught at third slip by Finlay Bean, although replays appeared to suggest that the former Hampshire batter looked hard done by.
The Tykes then put down a second slip catch of the day, this time Bean putting down Labuschagne’s thick edge off Edwards, with the Australian Test star on 23.
Labuschagne, in particular, and Kiran Carlson then capitalised on some loose bowling, Edwards particularly suffering, to build a fourth-wicket partnership of 52 before Carlson got an inside edge on George Hill’s delivery, drawing a magnificent diving catch down the leg side by Jonny Bairstow.
A lazy-looking flick to Matthew Fisher at mid-wicket cost Chris Cooke his wicket off the bowling of Jordan Thompson, while Michael Neser left a straight one from Edwards, who also had Billy Root caught in a six-strong cordon by substitute Jonathan Tattersall.
A good afternoon was not, however, perfect for Yorkshire, for whom Ben Coad left the field in the 36th over indicating he had a groin problem. Although he did return to the field it may not have been mere coincidence that he didn’t bowl for the rest of the session.
Notts 46-2 v Lancashire 214
James Anderson v Haseeb Hameed is a really good battle on the brink of tea at Trent Bridge.
Hameed survives for now and Jimmy is one of those moods where he can't believe he's not taken a wicket yet.
One over left before tea.
Derbys 99-0 v Leics 122
Derbyshire absolutely and totally in control at the Incora County Ground after bowling out their East Midlands rivals in just 39.5 overs earlier in the day.
Haider Ali is just two runs away from a first 50 for the county at tea, with Harry Came on 39.
Leicestershire have tried five bowlers so far, but have yet to reproduce the penetration that Derbyshire - especially Henry Brookes - achieved earlier in the day.
Hampshire 229 all out v Warwickshire
To say this one has ebbed and flowed would be an understatement.
Hampshire have gone from 83-1 a ball before lunch to 137-7 and are now 229 all out afer Mo Abbas holed-out to Alex Davies two balls before tea was due.
Fletcha Middleton made a fine 49 before falling just after lunch to Chris Woakes who has 3-45 while Chris Rushworth has 3-38.
James Vince was stranded on 75 from 92 balls after clubbing two sixes off old chum Danny Briggs in the previous over, but will be disappointed to have lost Ian Holland, James Fuller and Kyle Abbott to avoidable dismissals.
Yorkshire v Glamorgan 215-8
Image source, Rex FeaturesOnce the third-wicket partnership of Sam Northeast and Marnus Labuschagne was broken shortly after lunch, Yorkshire have taken Glamorgan wickets at regular intervals and should be in a position to be batting before the close of play.
George Hill took the key wicket of Labuschagne for 65, while Mickey Edwards has taken 3-54, but Ben Coad going off injured will be a concern for the home side.
Essex 204-3 v Surrey
An interesting move by Surrey, who hand the ball to England's Will Jacks for the first time today. What can he do with his off-breaks?
It's a good first over - a maiden to Matt Critchley.
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Ollie Robinson takes 7-59 for Sussex at New Road. Is he a certainty to be in England's Test attack for the Ashes series? If not, who should be the first-choice seamers for Ben Stokes and Brendon McCullum. Let us know your thoughts.
Worcs 264 v Sussex 4-0
The final session of the day is under way at New Road and four leg byes gets the Sussex score moving.
Will we see Steve Smith in the middle this evening? Worcestershire are going to need to take three wickets to bring that about.
Tom Clark has been promoted to open with Ali Orr as Tom Haines isn't playing in this game.
Essex 204-3 v Surrey - tea
Nick Gledhill
BBC Essex
After the early loss of Dan Lawrence this afternoon, an unbeaten century stand between Tom Westley and Matt Critchley was exactly what the home side needed.
They had to work hard, Westley adding just 37 in the session and doing particularly well to survive two searing yorkers in the same Kemar Roach over.
Critchley, with his fourth fifty this season, is now delivering the Championship runs that Essex were hoping for when they signed him from Derbyshire.
The pitch is playing well and, despite their long lower order, Essex are set to become the first side to score more than 300 against Surrey this season.
Somerset v Northants 137-4 - rain stopped play
Anthony Gibson
BBC Radio Somerset
It's raining again, and judging by the rainfall radar - currently being pored over by the two umpires and head groundsman Scott Hawkins - that will probably be it for the day.