AS the media chatted on the steps of Bute House waiting for the famous black door to open yesterday, the talk was as much about the first decent sunshine of spring as politics.

A couple of optimistic reporters were even sporting Ray Bans.

Few anticipated the thunderclap that awaited them within.

Since the morning after the Brexit vote, when she declared a second referendum “highly likely”, the First Minister has seemed engaged in a never-ending tease campaign.

Somehow the likelihood of a referendum was forever increasing, but it was never in sight.

Despite being “all but inevitable”, it was also strangely intangible.

That ended at 1140 am, when Ms Sturgeon said Scotland “will have a choice” on whether to stick with Brexit in the UK or try an alternative under independence, most probably between autumn 2018 and spring 2019, when a Brexit deal comes into focus.

Although most present already sensed a referendum was coming - SNP ministers have been in campaign mode for weeks - it was still quite a thing to hear.

The First Minister made a few faint nods to a last-minute compromise with the UK Government over her plan to keep Scotland in the EU single market, but only just.

“Even at this late stage, I am not turning my back on further discussions should the UK government change its mind and decide it is willing to agree to our compromise proposals,” she said, offering merely “further discussions” rather than calling off a referendum.

Far more frequent were complaints about shoddy treatment by Westminster.

“Our efforts at compromise have instead been met with a brick wall of intransigence. The language of partnership has gone, completely.”

As an example of that broken relationship, she cited the Prime Minister’s imminent announcement on the triggering of Article 50.

Despite Theresa May saying she wanted a UK-wide approach to Brexit, Ms Sturgeon was still in the dark about the timing, even though it might be just 24 hours away.

Confidently cracking jokes with her audience, the First Minister deftly pulled the rug from under Mrs May’s announcement, while making it synonymous with Scotland's future.

She also avoided the partisan atmosphere of this week’s SNP conference in Aberdeen.

Instead of speaking against a sea of giant foam hands, she made the most of her official residence, insisting she was acting in Scotland’s interests not merely playing to her party’s rank and file.

Asking the Scottish Parliament’s consent next week about a transfer of referendum powers will continue that restrained approach.

But there remained gaping holes in the case for independence, most familiar from 2014.

Time and again, she said voters would be able to make “an informed choice” when they went to the polls.

But asked which currency an independent Scotland would use, she said “all in good time”.

That is unlikely to convert any No voters suspicious of the SNP’s fiscal credentials.

Despite Ms Sturgeon saying she had a clear mandate for a referendum derived from the Brexit vote, she also failed to say such a referendum would reverse Brexit.

Instead, there would be a new relationship with Europe different to the rest of the UK - implying economic or physical borders - but details would have to wait.

It will be hard to argue that Scotland being dragged out the EU demands a referendum, but a Yes vote will not necessarily return Scotland to the EU.

One reason for caution is that a third of SNP supporters voted Leave in 2016, and the party needs to keep them to win next time.

EU or single market membership also means freedom of movement, so immigration, which was peripheral to the 2014 debate, could be integral to a second plebiscite.

The SNP knows EU-style open migration is as unpopular in Scotland as in England.

Hence Ms Sturgeon’s inclusion of numerous other arguments in favour of independence to dilute the EU dimension - the democratic deficit, being ignored, possible Tory rule to 2030, and the recurring question of what kind of country Scotland should become.

Economic questions also loom large.

The recent confirmation by Andrew Wilson, chair of the SNP’s Growth Commission, that oil revenue is now assumed to be zero after independence, means the country could start life outside the UK with a deficit around 10 per cent, the level the UK last faced after the 2008 Crash then reduced during years of painful austerity.

As Paul Johnson of the IFS pointed out yesterday, public spending in the Scotland is also £1000 a head higher in Scotland than the rest of the UK.

Addressing a raging deficit while trying to fund above average spending with average tax revenue could mean deep cuts, big tax rises, or some of each.

The weather may have been set fair for Ms Sturgeon's announcement, but there are surely storms and squalls ahead.