Offshore islands as barriers to fog

June 7th, 2021 |

GOES-16 True-Color imagery, 1301-2101 UTC on 7 June 2021 (Click to animate)

Moist air that moves from the mainland USA to over the north Atlantic will often induce fog formation over those cold shelf waters.  This is a common occurrence (see this blog post, for a recent example) GOES-16 True-color imagery, above, from 1301-2101 UTC on 7 June 2021, shows the northeastward progress of a fog bank. Note how Block Island, Martha’s Vineyard and Nantucket all served as barriers to the fog.  Such behavior is most likely when a strong inversion is in place.  The closest upper air sounding, Upton NY, over eastern Long Island, below, from this site, did show a very strong surface inversion at 1200 UTC as well as brisk southwesterly winds in the lower levels of the atmosphere. The strong inversion would also allow the bow wake to form upwind of the islands, as observed. (The inversion at Upton persisted through the day! 00Z 8 June sounding is here)

Fog does not penetrate far inland along the coast. Solar heating over land will induce vertical mixing that evaporates any fog over land. A similar event occurred on 8 June.

Upton, NY, rawinsonde, 1200 UTC on 7 June 2021 (click to enlarge)