The Ocean Effect

I find today's weather particularly interesting because it shows the immense power of bodies of water like oceans or lakes.

Here is a look at forecasted temperatures for 2 p.m. today from the National Weather Service (NWS).

NWS forecasted temps for 2 p.m. (NWS) 

And here are current temperatures throughout the Northeast from Weather Undergrounds Wundermap (I am writing at 1:20 p.m. eastern time).

1:20 p.m. temperatures (Weather Underground)

Notice that in both of these temperature maps, inland areas are (and forecasted to be) much warmer than areas along the coast like Maine, Long Island, and Nantucket. Although one would think that areas at a higher latitude in the northern hemisphere would typically have cooler temperatures, we see the ocean effect at play here.

The equation relating heat energy (Q) and temperature change (△T) is Q = m*c*△T, where m is the mass of the substance of interest and c is that substance's specific heat. Water has a relatively high value for c, meaning that it requires lots of energy Q to change T by a small a small amount.

What does this mean for the weather that we see today? Well inland, temperatures are much warmer. This is because there is no body of water limiting the temperature increase for inland areas. In other words, Q is low for these inland areas. It hasn't required much energy to warm these inland areas today. On the flip side, near the ocean, lots of energy is required to warm the land because m and c are both large. Therefore, lots of energy (Q) is required to warm the temperature a small amount, and we are seeing cooler temps near the ocean today.

In the winter time, the ocean effect has the opposite effect, causing interior areas to generally be cooler, while spots along the coast remain more temperate. 

The ocean effect is particularly evident in California, where a place like Santa Monica on the Pacific ocean can be 75 °F, while temperatures in Pomona (about 40 miles east of Santa Monica) can be near 100 °F.