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Why does I-95 seem important to NC weather?

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I’ve been asked this question a few times: Why does it always seem like storms are going east of I-95, west of I-95, or right along I-95 in North Carolina? Is it just a convenient landmark that most people recognize, or is there something else to it?

As recognizable as I-95 is, the answer is that there’s more to it. I’ll explain, although I am running the risk of over-simplifying it here.

If you look at a road map of North Carolina and a relief map of North Carolina next to it, you will see that I-95 basically runs along the border between the state’s coastal plain and the piedmont – two of the three major geographic regions of the state.

Each region has its own characteristics that can affect the weather and climate including elevation, soil types, and available moisture. The mountains’ higher elevations tend to get more snow. The piedmont tends to have greater variations in weather through the year. The coastal plain has more available moisture and more moderate temperatures with the ocean on its eastern edge.

Often when storms are moving across the state from west to east, they lose some of their energy as they cross the mountains. Depending on many factors, a storm might reorganize as it reaches the piedmont, or it may not regain its former glory until it hits the coastal plain.

On the flip side, if a hurricane or other coastal storm is approaching from the Atlantic side of the state, it may only affect the coastal plain if it stays far enough out to sea. If it moves closer to shore, the piedmont might be affected, but in a different way than the coastal plain. Take, for example, our typical winter coastal storms that move up the Atlantic coast to become Nor’easters. If the storm stays far enough off shore, the coast may just see rain. If it moves right up the coast line and cold air is in place over the piedmont, we in the Triangle may see snow or a wintry mix. Sometimes the mountains get snow from those systems and sometimes they don’t. It depends on the size of the storm and its proximity to shore, among other things.

During the winter, the ocean tends to moderate the temperature near the coast by keeping it warmer because large bodies of water take longer to lose their heat than the drier air in the atmosphere. (They also take longer to gain heat once the weather starts to warm back up.) The warmer ocean waters affect the air nearby and keep temperatures at the coast milder than they are inland.

Elevation and soil types can also play a role in the weather, but I will save those topics for future blog posts.

In the meantime, the next time you hear a meteorologist say, “along or east of the I-95 corridor,” you will know why.

road map of NC

Road map of North Carolina, credit: geology.com.