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Well, let's see.
What do we have ?
For starters, the anal vein very clearly does NOT reach the wing margin. Hence, it is Ceromyia, rather than Ceranthia. Moreover, Ceranthia are less grey.
Else:
The Cu-vein is bare. The R1-vein seems bare as well, but difficult to see. The R4+5 vein has only a few bristles.
The abdomen has lateral discals.
The third antennal segment is remarkably elongated and the arista is thickened on basal half or slightly more.

There is only one species with these kind of features, fasten your seatbelts;

Female Ceromyia monstrosicornis.

Date and habitat fit.

Now, this is an extremely rare species indeed and I'd loved to be able to check many other relevant features. But I am not.
I'd say the identification is 90 + or even 95 + % certain.
Up to you if you'd call it monstrosicornis or ?monstrosicornis.

And please submit to the gallery for later use, we'd probably have to wait 25 years for the next shot.

Theo