Monday, August 25, 2014 - 5:28pm

What is the Recipe for a Thunderstorm?

Weather Talk

POSTED: Tuesday, July 8, 2014 - 12:41pm

UPDATED: Wednesday, July 9, 2014 - 2:14pm

The atmosphere needs the right ingredients and conditions, mixed together in a precise way to produce a thunderstorm

Just like when you are baking the perfect dessert or making that special dish,  you need the correct ingredients in the precise amounts mixed together in the right order in order for the food to come out tasting the way it should. The same goes for the recipe in creating a thunderstorm, you need the right ingredients in the proper amounts mixed together in the right atmospheric conditions. In today’s “Weather Talk”, I will talk  about what ingredients or conditions and mechanisms are needed in our atmosphere to create and fire off thunderstorms.

The National Oceanic and Atmospheric Administration (NOAA) National Weather Service says there are approximately 1,800 thunderstorms occurring at this moment, resulting in about 16-million thunderstorms each year. Most thunderstorms last about 30 minutes and are typically about 15 miles (24 km) in diameter. The two biggest threats associated with most thunderstorms are lightning and flash floods. If we understand the basic components or ingredients of a thunderstorm, we then understand why they occur most often during the warmer months. Thunderstorms thrive under certain conditions.

Here are the main ingredients needed in the creation of a thunderstorm:

• Moisture
• Instability (rapidly rising warm air)
• Lifting Mechanism

The two most crucial ingredients in a thunderstorm are moisture and warmth. So it makes sense that thunderstorms happen more often in the spring and summer, especially in the more humid areas like the southeastern United States. The high humidity, in combination with warm temperatures, creates massive amounts of warm, moist air rising into the atmosphere where it can easily form a thunderstorm.

Water temperature also plays a large role in how much moisture is in the atmosphere. The National Weather Service reminds us that “warm ocean currents occur along east coasts of continents with cool ocean currents occur along west coasts. Evaporation is higher in warm ocean currents and therefore put more moisture into the atmosphere than with cold ocean currents at the same latitude. Therefore, in the southeastern U.S., the warm water from the two moisture sources the Atlantic Ocean and Gulf of Mexico. This helps explain why there is much more rain in that region as compared to the same latitude in Southern California.”
During the southwestern US “monsoon season”, the main source of warm, humid air for the Borderland comes from the Gulf of Mexico, some from the Baja of California/Pacific, and a weak stream that travels all the way from the Yucatan north over mainland Mexico.

The atmosphere is considered to be unstable if a bubble or parcel of air is pushed upwards and it continues to rise or it is pushed downwards and it continues to sink.
As this bubble or parcel of air rises, it also cools and some of the water vapor will condense on debris ( dust, sea salt, pollution), which turns into cumulus clouds. The energy released from this condensation causes more condensation which grows the clouds sometimes into thunderstorms.

Lifting Mechanisms
A source or mechanism is normally needed as the initial start of a thunderstorm. This “Spark” initiates the upward motion, something that will give the air an upward bump. This upward nudge is a direct result of air density.
The National Weather Service explains air density as: “Some of the sun's heating of the earth's surface is transferred to the air which, in turn, creates different air densities. The propensity for air to rise increases with decreasing density. The difference in air density is the main source for lift and is accomplished by several methods.”
Differential Heating-The sun's heating of the earth's surface is not all the same. A parking lot or a paved street heats up faster than a grass covered golf course or a body of water. A body of water will heat slower than the land next to the water. This produces two air masses next to each other with different densities. The cooler air sinks, pulled toward the surface by gravity forcing up the warmer, less dense air, creating thermals. When these thermals rise, the water vapor in the air condenses and forms clouds. Strong thermals or rising parcels of air can produce thunderstorms.

Mountains or Terrain- A traveling air mass runs into a mountain and forced upward because of the ascending terrain. Strong winds can also force these air masses up a mountain. Up Slope thunderstorms are common in our region over our area mountains and especially the Rocky Mountain west during the summer monsoon.

Fronts, Drylines and Outflow Boundaries

Fronts- are the boundary between two air masses of different temperatures and therefore, different air densities. The colder, denser air behind the front lift is warmer with abruptly less dense air . If the air is moist, thunderstorms will often form along the cold front.

Drylines-are the boundary between two air masses of different moisture content and separates warm, moist air from hot, dry air. Moist air is less dense then dry air. Drylines, therefore, act similar to fronts in that a boundary exists between the two air masses of different densities. The air temperature behind a dryline is often much higher due to the lack of moisture. That alone will make the air less dense, but the moist air ahead of the dryline has an even lower density making it more buoyant. The end result is air lifted along the dryline forming thunderstorms. This is common over the plains in the spring and early summer.

Outflow boundaries -behave similar to fronts. As rain cools, colder air rushes downward from a thunderstorm hitting the ground and pushing up more warm, humid surface air to create more storms. This happens most often when down bursts occur from a dying thunderstorm and the air is dragged towards the surface by the rain, hail, and colder air.

Now you can better understand how all these ingredients and atmospheric conditions come together to form a thunderstorm. Warm, humid air are the keys, then we need a mechanism to lift that air upward and finally a dash of instability to keep air rising. Hopefully all these ingredients come together many more times over the next few months here in the Borderland to help our parched desert come back to life!

Chuck DeBroder, Chief Meteorologist
KTSM, NewsChannel 9, NBC, El Paso, TX

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