Might be... Never thought you can get waves on a flatland. I suspect it must have something to do with that siberian high. Never seen a QNH of 1043 hPa before... Do you have any idea where I could find some additional info on the subject?
On my recent met classes I was told that standing waves could exist many hundred nautical miles away from the mountains. So it is not uncommon at all to get waves over the flat land. According to the UK AIC (144/1997 pink160 30th December) usually waves extend about 50-100nm to the downwind side of mountains but those has been witnessed extendind as far as 250nm from the Pennines or even 500nm from the Andes!
Best Regards,
AM