Even in the hinterlands of myth, the notion of sex with snowmen seems rather a neglected subject. Hans Christian Andersen tells of a snowman who, promisingly, falls in love, though the object of his affection turns out to be a stove rather than a mortal. One looks in vain for much evidence of an eroticised Frosty in, say, Angela Carter: evidently, such a combination of the twee and the sensuous is too much for most committed fabulists.

Kate Bush, however, is not one to shirk that kind of creative challenge. The centrepiece of 50 Words For Snow, her first album of new songs in six years, is a 14-minute love song to a snowman, one made by her own hands and named “Misty”. Logic, at this point, would suggest that the snowman is a metaphor for a particularly short-lived lover, or a notably frigid one. The evidence, though, seems to demand a more literal explanation. When she wakes after their “one and only tryst”, he has melted away, leaving wet sheets and “dead leaves, bits of twisted branches” on her pillow. Should ambiguity remain, the LP’s cover dissolves it utterly, a bas-relief, apparently made out of ice, portrays a snowman’s puckered lips touching those of a young girl.

It is not the first time Bush has created an image that induces cringes of embarrassment rather than gasps of wonder. “Misty”, though, is extraordinary: a torch song, driven along by the gently kicking jazz of Steve Gadd (drums) and Danny Thompson (bass), that makes nuanced romantic currency out of a truly preposterous idea. “Misty” forms the climax of what we might tentatively call the first movement of 50 Words For Snow; three piano-led pieces (“Snowflake”, “Lake Tahoe”, “Misty”), 35 minutes in total, that take their cues from “Mrs Bartolozzi” and “A Coral Room” on 2005’s Aerial, and from the stripped-back, wistful version of “Moments Of Pleasure” on this year’s Director’s Cut.

As that last album of reworkings proved, Bush’s voice is not what it was. Where once it soared and ululated in such an untethered way, now it is often deeper, warmer, evoking a sort of curdled soulfulness. One of the marked poignancies of 50 Words For Snow is that, while Bush’s subject matter is more evanescent than ever, she addresses it in much more human and earthy tones. Ten-and-a-half minutes into “Misty”, as she details what the snowman has left behind, her voice cracks on “stolen grasses from slumbering lawn”, intensifying the emotional heft of the song so much that its subject matter – to recap: sex with a snowman – is rendered profound rather than ludicrous.

“Snowflake” and “Lake Tahoe”, meanwhile, find Bush contracting out some high notes to other singers. On “Snowflake” – narrated, perhaps inevitably, by a falling snowflake – the lead is taken by her 13-year-old son, Albert McIntosh. McIntosh already has quite a recording history, having talked with the birds on Aerial, been eulogised by his mother on “Bertie”, and appeared in Autotuned form on the Director’s Cut version of “Deeper Understanding”. This time, though, his voice is untreated, revealing its uncanny potency; it sounds as if Bush is being rechannelled through the larynx of an ingenuous choirboy.

Some of the serious lifting on “Lake Tahoe” is handled by two classical singers, Stefan Roberts and Michael Wood, with their Schubert-like passages alternating with bluesier ones sung by Bush. These are slow, long songs, given coherence and momentum by Bush’s piano lines, gracefully reminiscent of Keith Jarrett. From austere, absurd materials, the cumulative effect is remarkable.

It would, though, be expecting a little too much for even Bush to sustain such a heightened atmosphere for another half hour. Consequently, the second phase of 50 Words For Snow is more diverse and less satisfying. “Wildman” is fine, a sensual pursuit of the yeti (though, amid a scree of esoteric reference, that name is never used) delivered by Bush as a kind of incantatory, whispered rap. The music is a sprung cousin to “Somewhere In Between” from Aerial, the chorus shared by Andy Fairweather Low; another musician from a generation, slightly older than Bush, that she has called on throughout her career. That generation, often rather conservative, has magically sounded radical in Bush’s company. Not all dinosaurs, though, can be taught new tricks so easily. “Snowed In At Wheeler Street” charts the progress of two lovers who keep reconnecting at crisis points in history, and features Bush drawn into a stand-off with one of her earliest heroes, Elton John. The backing is nearly ambient, but Bush chronically over-emotes, as if she is straining to match Elton’s histrionics rather than forcing him to play her more subtle game.

The spotlight is also shared on the title track, with Stephen Fry cast as Dr Joseph Yupik (Yupiks being an Eskimo tribe of Siberia and Alaska), goaded by Bush – “Come on Joe, you’ve got 32 to go!” – into finding 50 synonyms for snow. The droll neologising “Wenceslasaire”, “spangladasha”, “shnamistoflopp’n”, is charming enough, and the soft urgency of the music reiterates the genteel rave influence that crept into the second half of Aerial. But at the same time, the way the track is predicated on Fry’s reputation as bibliophilic fount of all knowledge seems somehow crass. Given how much of Kate Bush’s appeal is built on an image of her being blissfully disconnected from the real world, it is disappointing to imagine her coming up with the concept while slumped in front of QI on a Friday night.

This, then, is the paradox of 50 Words For Snow. Kate Bush has never made a record that seems so ethereally disdainful of convention, of the parameters, themes and expectations of a simple pop song. But at the same time, she has never seemed so normal: a little indulgent to celebrity; acutely aware of how time has brought mortal vulnerability to her voice.

50 Words For Snow ends with another beautiful and glacial piano song, “Among Angels”, where she identifies seraphim clustered around her subject. It is, perhaps, a blessing and a curse that Kate Bush can no longer be mistaken for one herself.

John Mulvey