If you live close to the Chesapeake Bay, you are very familiar with the late spring and early summer phenomenon of the marine layer. Thick fog or low cloud cover can easily overtake the immediate shoreline on a mild day, possibly ruining your plans to soak up some afternoon sun! Sometimes, the clouds migrate further inland, like they did today, overtaking the DC Metro area. But by mid-morning, the clouds were pretty much gone! What gives?
First of all, It takes a lot longer for water to warm up than air. So while our average high temperature is now in the 70s, the water offshore in the Atlantic Ocean is still in the 50s, and even 40s in some spots! Even the Chesapeake's surface water temps are still in the 50s for the most part.
A persistent wind from the east will bring some of this cooler, moisture-laden air inland. On Monday and Tuesday of this week, we had to deal with dreary weather that was brought in by the east flow. After a sunny Wednesday, a temperature inversion developed overnight under clear skies. A temperature inversion occurs when temperatures rise with ascending height (this is the opposite of what's normal). An inversion can act as a barrier to opposing air flow. But as the sun rose, the temperature inversion quickly dispersed, allowing the easterly wind to bring some Atlantic moisture in to the DC Metro in the form of low clouds.
The marine layer didn't stick around very long today, because the strong May sun continued to heat the atmosphere, mixing through the low cloud cover and dispersing it. However, with similar conditions persisting tomorrow and Saturday, we might see this same deck of morning clouds again before the week is over.
The marine layer is usually gone by the summer here in the DMV, because the relatively shallow water of the Chesapeake Bay warms into the upper 60s and 70s.