Kevin Myatt is The Roanoke Times' weather columnist.

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Sometimes a term can have two very different meanings.

The sentence "Roanoke was affected by a wedge Thursday" could conjure up two completely different images of "wedge" to weather-involved people.

First, the one that is common locally, and was true on Thursday.

A "wedge" to folks along and east of the spine of the Appalachians (roughly along the Tennessee-North Carolina border and then northeastward along the Virginia-West Virginia border) refers to the frequent occurrence when cool, moist air is pressed against the mountains by east or northeast surface winds.

This occurs when high pressure in southeast Canada or New England is present to press cooler air from that region southward.

The Appalachians form a sort of dam that doesn't allow the cooler air to move westward past them. This allows the cool air to pool and thicken on the east side of the mountains.

In winter, we commonly call the wedge a "cold air damming" event. It can have a major impact on winter precipitation situations. Warmer air full of Gulf of Mexico moisture overriding the mountains into an especially cold wedge can trigger ice or snow, depending on the depth of the cold air.

On Thursday, Roanoke was indeed affected by a wedge.

This one was aided by the coastal low that has been spinning just off the East Coast the past few days. It's counter-clockwise spin pulled east and northeast winds into the region, wedging damp, cool air off the Atlantic against the mountains.

As a result, low clouds persisted much of the day and temperatures stayed below normal for this time of year, rising only into the upper 60s and low 70s.

A thicker wedge in midsummer can sometimes result in all-day fog and drizzle with temperatures staying in the low to mid-60s.

But while people's opinions differ about the value of cool, damp weather in summer or early fall, we should all be able to agree that we would never want to directly experience the other kind of meteorological wedge.

"Wedge" is also a term commonly used to describe a tornado that is wider than it is tall.

These are the tornadoes that look like a blob of cloud rolling along the ground below very low base clouds-- no funnel or cone, just a short cylinder between cloud and ground.

Some of the more destructive tornadoes have been wedge-shaped, and certainly, wedges are among the most ominous in appearance.

Thursday's cool air wedge cut down on the instability that was present Wednesday for some heavy thunderstorms.

And the cool air wedge just about precludes any chance of a wedge tornado happening.

Weather Journal appears on Monday, Wednesday and Friday.