The phrase "almost severe" is correct and usable in written English.
It can be used to describe a situation or condition that is close to being severe but not quite there.
Example: "The storm was almost severe, with strong winds and heavy rain, but it didn't reach the level of a hurricane."
Alternatives: "nearly severe" or "borderline severe".
His playing is refined, almost severe.
Its 72 rooms are furnished in a sleek, almost severe fashion, but the marble baths are elegant and spacious.
In contrast, the overall effect of the 11 songs on "Telling Stories" -- first-person narratives all -- is one of almost severe design.
"I had noticed that Mr. Clemens always assumed a dignified pose at such times, with a serious, almost severe expression of face," she wrote.
Then there's Sasabune, which wants you to know that you're entering a world — well, a white-walled nook with an almost severe lack of adornment — in which the rules of engagement are established and mostly unwavering.
The church itself, like most 18th-century Spanish mission sanctuaries, is simple, almost severe, its cool stone walls rising around rough wooden pews; its now-worn facade was once ornately decorated with tile and colorful frescoes.
The limestone facade is severe, almost spartan, like the empty buildings in de Chirico's Surrealist paintings.
We need to accept that there is a nascent human stage in our development where we – all of us – have severe and almost dangerous impulses to chase boys with haircuts over war memorials.
Putin's resentment of Clinton was always manifest; it is almost as severe as Trump's.
Before the concerto, Esa-Pekka Salonen delivered an impressively precise and almost intimidatingly severe account of a selection from Prokofiev's three suites from his Romeo and Juliet ballet score.
The buildings are old but not in a cozy way; they are eerie and dark, and the cases here are almost all severe.
