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What Is A Dry Line, And Why Does It Create Severe Weather?

You've probably heard of a 'dry line', but what exactly is it, and why does it create severe weather? We're going to dig into the details in this article, but first, here's a video of a line of storms that formed from a dry line earlier this year in west Texas. Check it out:

What Is A Dry Line?

Simply put, a dry line is a boundary between moist and dry air masses. Unlike a cold or warm front, one airmass is not rapidly overtaking the other. Additionally, the temperature on either side of a dry line will be similar, meaning there isn't a large temperature gradient.

The biggest difference in the air masses lies in the moisture content.

Where Dry Lines Form

A dry line will typically form north to south in the southern and central planes of the United States. This line represents the boundary between the moist air that is drawn up from the Gulf of Mexico, and the drier air blowing across the deserts of the southwestern United States and northern Mexico.

Sometimes you'll hear a dry line referred to as a Marfa front, after the town of Marfa, Texas. This area commonly sees dry lines during spring and early summer, as well as up and down tornado alley.

Lifting Action Created By Air Mass Differences

The reason dry lines create thunderstorms is due to the difference in density of the air masses.

The point where the two air masses and winds converge is the dry line, that's where the convection starts.

The dry, more dense air acts like a wedge lifting the less dense moist air. This behavior is almost like a mini cold front, but without the strong shearing motion of a cold front, the rising action of the boundary area is typically reduced.

However, with enough wind shear aloft, significant lifting action can occur, like what you saw in the video at the top of the article.

From sunrise to sunset, a dry line will generally move towards the east and reverse its' direction overnight. The point where severe weather is most likely to form along the dry line happens as it moves to the east in the late afternoon.

How To Identify A Dry Line

The easiest way to identify a dry line is with a surface analysis chart. An orange scalloped line means a dry line is present.

You can also identify a dry line by looking at a graphical depiction of the dewpoint.

Another way to identify a dry line is with the weather associated with the east and west sides. You can expect a dry line to have cumuliform-type clouds with extensive vertical development on the east side. On the west side you might see clear skies, or with an unusually strong dry line, dust storms that are caught in the dry line's updrafts.

How Does It Affect Aviation?

Because a dry line doesn't have a powerful temperature gradient like a cold front, the chances of developing severe weather are reduced, but not eliminated. While a cold front can develop severe weather like squall lines, if a dry line develops convective activity, it's typically in the form of individual cells. However, thunderstorm cells from a dry line can still mature into supercells, given enough wind shear.

Have you ever experienced a dry line thunderstorm? Tell us about it in the comments below.

Nicolas Shelton

Nicolas is a private pilot from Southern California. He is currently studying at Purdue University, where he is working on advanced pilot ratings. You can reach him at nicolas@boldmethod.com.

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