Turbulence by Giles Foden.
Henry Meadows is a meteorologist, and in the brief sections of the book set in the "present", he's on board a ship made largely out of ice (or, more specifically, a more melt-resistant blend of ice and wood pulp called Pykrete) travelling from Antarctica to the Middle East in 1980 as part of an experimental drought-relief system.
This framing device really just provides a hook to hang the real story off, the real story being that of Meadows' involvement as a keen young twentysomething junior meteorologist in the planning for the 1944 D-Day landings, and specifically the long-range weather forecasting required to fix a date for the invasion in advance.
There's an obvious problem, quite apart from the one of long-range weather forecasting (over a timescale greater than a couple of days) being notoriously error-prone: not only are various advantageous weather conditions (full-ish moon, clear skies, not much wind) required, the element of surprise is also essential and of course the Germans have perfectly capable meteorologists of their own. So the Allies need an edge over the enemy, and Meadows is dispatched to Scotland to sound out the man who just might provide it, Wallace Ryman. Ryman is a maverick meteorologist, who doesn't play by the rules, but dammit he gets results, and those results include the Ryman number, a coefficient which helps make sense of turbulence, something which otherwise wrecks the (already dicey) accuracy of forecasts.
The trouble is, Ryman doesn't seem to be wholly on board with the whole war thing, and seems to harbour some pacifist tendencies, which have led him to largely give up the old meteorology game (hardest game in the world, the old meteorology game) and focus instead on some arcane mathematical theorems for bringing about world peace. Well, you've got to have a hobby, haven't you? So Meadows' assignment is: set up a fake weather-monitoring station just down the road from Ryman's place on the west coast of Scotland, "bump into" Ryman around the neighbourhood and try to get some information out of him.
Although Meadows does strike up a tentative friendship of sorts with Ryman, and they do have some discussions about weather, he doesn't get a lot of useful information out of him. What he does get is a couple of unsettlingly sexually-charged encounters with Ryman's wife Gill, one of which results in a bit of a slapstick oops-oh-no-I've-fallen incident during which bodily fluids are exchanged, though probably not the ones you're thinking of.
All Meadows' ham-fisted scheming comes spectacularly unstuck when his well-intentioned (though slightly drunken) attempt to bring down a Nazi Junkers reconnaissance plane with some booby-trapped weather balloons results, via a rather unlikely sequence of events, in Ryman's death. So with the chances of getting any usable information out of him having reduced from small to zero, Meadows is re-assigned (in some disgrace) to the team collating the various weather readings and predictions from an international team of experts, a more challenging job than it might sound given that none of them seem to be able to agree on anything.
But then Meadows notices some small anomalies in the readings from one of the weather ships in the vicinity of Iceland (no, the other one) and starts to get an inkling of perhaps being able to put some of Ryman's theories to use after all. After a quick dash to the Isle of Wight to make sure the instruments weren't malfunctioning, during the course of which he has a brief reunion with Gill, he returns to the pivotal invasion planning teleconference in the nick of time to persuade everyone that the invasion date should be changed from June 5th to June 6th, as that day will be fine, honest.
And the rest is, quite literally, history. As with all novels of this sort, unless you're going to do some serious post-modern fucking with your audience then the broad details of what's going to happen in the end are not in doubt; in this case that D-Day happens on June 6th 1944 and despite the horrendous casualties is ultimately the platform for the Allies winning the war. So you have to make the story that converges on the known point interesting enough to hold the reader's attention, and Turbulence certainly succeeds there, though not without the odd lumpy moment. As expertly as the circumstances are set up in advance Ryman's death seems contrived and frankly implausible, and while Meadows (from his narrative position in 1980) seems to allude several times to events that happen well after the war is over we never hear about any of that in the main text; instead it's left to what purports to be the text of a commemorative lecture given in 1984 by a German counterpart of Meadows to fill in some of the blanks. And with any novel that features science-y stuff as a central plot feature there's a struggle to fit the necessary exposition in without it being narratively implausible; there's only so much "as you know, Bob, Bernoulli's principle states that...." that you can do without coming over all Basil Exposition.
It's good, though, while probably not quite as good as Foden's first and most famous book The Last King Of Scotland (also filmed). If I'd been obliged to read it without knowing who the author was I'd have made a reasonably confident guess at William Boyd, which I should stress is a compliment. There are obvious parallels to The Book Of Ebenezer Le Page in terms of subject matter, in that World War II features heavily as a plot device. Other novels to feature World War II as a central plot device include Free Fall, The History Of Love, The Office Of Innocence, Island Madness, Restless and The Nature Of Blood. Note that that list is by no means exhaustive.