Wintertime Es on 10m?

In amongst the DX calls today I notice callsigns from 4 European countries. I assume the propagation was F layer or F layer backscatter, but it could be wintertime Es which peaks in the northern hemisphere around Dec and Jan. Signal levels suggest Es may be more likely. All the more reason to use WSPR to seek out fleeting Es openings that might otherwise go unnoticed at any time of the year.