The normal rule of thumb is that if something looks too good to be true, it probably is. And it has to be said that many of the details of YouGov's new Scottish poll seem almost unbelievably good for the Yes movement in general, and the SNP in particular.

After two calendar years in which no YouGov poll had shown the Yes vote any higher than the 45% achieved in the 2014 referendum, all of a sudden it appears that Yes have essentially drawn level on 49%.

After a prolonged spell during which only a small minority of polls across all firms had suggested that pro-independence parties were on course to retain their majority at the next Scottish Parliament election, YouGov are now reporting that the SNP and Greens are set to effortlessly retain their dominance, with a projected 74 seats between the two parties, compared to the unionist parties' 55.

And even our assumptions about the limits of the SNP's realistic ambitions at Westminster have been rocked by numbers implying that Nicola Sturgeon will repeat her 2015 feat of winning more than 50 of the 59 Scottish seats.

On the latter point at least, there is a degree of corroboration for this poll from elsewhere, because the new Survation poll commissioned by Scotland In Union similarly suggests that the SNP would take 51 Westminster seats in a snap election.

What appears to be happening is that both Scottish Labour and the Scottish Tories are succumbing to a Britain-wide pincer movement from new pro-Brexit and pro-Remain parties, while the SNP vote remains remarkably untouched, and indeed has even strengthened somewhat. That may simply be because The Brexit Party and Change UK have very little to say to pro-independence voters.

As far as the independence and Holyrood numbers are concerned, YouGov are so far on their own in pointing to a major breakthrough, so it remains to be seen whether we'll remember this poll as a weird outlier or as the start of a new trend. But given how dramatically the polling landscape has changed across Britain over a few short weeks, there's nothing inherently implausible about the reporting of a major shift in Scottish public opinion. Remember that this is the first poll from any firm to ask the standard independence question since the end of last year, so it's entirely possible that something important has been brewing for quite a while without us even being aware of it.

One reason why the EU referendum result didn't produce the immediate boost for independence that many expected is that a minority of Yes voters drifted away due to their support for Brexit, while pro-European No voters seemed remarkably resistant to moving in the opposite direction. The details of the YouGov poll suggest that could finally be changing, with the 4% boost for Yes coming entirely from Remainers.

And is it really so hard to believe that the chaos of the last few weeks, and a near brush with No Deal, could have shocked even the most reluctant into reassessing their views on independence? Perhaps we can afford, very tentatively and very cautiously, to contemplate the possibility that, this time, the weather really has changed.