Standing waves upstream of Nova Scotia
GOES-16 visible imagery above (click to animate) shows the development of standing waves upwind of southwestern Nova Scotia. These winds developed in a region of low-level southwesterly (i.e., onshore) flow, as shown in the 1806 UTC image below that includes surface observations. Higher clouds are moving from a more westerly direction, suggesting veering and warm-air advection.
Note the very warm temperatures over interior Nova Scotia in the image below. This suggests a strong inversion such as is necessary to trap energy that is then manifest as the standing waves. Indeed, the Yarmouth, NS sounding at 1200 UTC shows surface temperatures near 12 C with temperatures closer to 20 C between 900 and 950 mb; that works out to be a potential temperature difference of 16.5 K across the inversion.
(Thanks to Richard DiMaio, Lewis University, for bringing this event to our attention!)