Plenty of sunshine has settled over most of central Pennsylvania during the morning, and with the exception of some afternoon clouds, the sun was expected to stick around through the afternoon.  Head out to sea, however, and there were plenty of clouds bubbled up over the ocean through morning and much of the afternoon.  Why the contrast?

There are a few factors working together to create this scenario.  First, we’ll consider conditions during the morning.  It was chilly, and winds were blowing out of the northwest.  Keep in this in the back of your mind; it will become important later.

Another point to ponder is simple density properties.  Warm air is less dense than cold air.  In the atmosphere, the air is constantly trying to work towards equilibrium, or a state of balance.  Simply stated, warm air will always try to rise in order to reach this balance because it’s a bit lighter.  Cold air will always want to sink because it’s heavier.

Now, let’s pull it all together!  Compared to land temperatures today across the Mid-Atlantic, sea surface temperatures across the ocean were much warmer.  Land temperatures through noon on Friday ranged from the 20s to lower 30s across the Mid-Atlantic.  Sea surface temperatures were in the 40s.  This may seem obvious, but air movement is guided by wind.  With a wind blowing from the northwest, the flow of air is out of the northwest.  This means a northwest wind pulls air from the northwest towards the southeast –the colder air sitting across the Mid-Atlantic is being moved southeastward over the ocean.  The result is cold air above warm air, which not a state of equilibrium.  To correct this, warmer air sitting directly above the sea surface begins to rise.  Rising air cools and condenses on the way up, and the end result is clouds!

Winds are expected to shift to the south late Friday afternoon, and this will allow the cloud cover offshore to diminish.