Flying Cloud Photography

Recently because of my frequent travels to Kansas, it seemed wise to learn more about violent weather.  I took a course to become a weather spotter which only increased my need to know about severe weather. I am sort of the opposite of a storm chaser - I really want to see storms from afar.  This was not the case this last Friday

Shelf cloud vs. Roll cloud

A shelf cloud, also known as an arcus or arc cloud, may be the most frequently submitted cloud photo to our weather.com photo gallery and Facebook page. Based on their appearance, we certainly understand why. 

A more rare variety of this type of cloud, a roll cloud, resembles a giant rolling pin in the sky. The first two photos in the slideshow from Lake Hendricks, Minnesota, on June 20, 2015, show a terrific example of a roll cloud.

To understand how roll clouds form, we first must explain how shelf clouds develop.

Shelf clouds are typically seen at the leading edge of a thunderstorm or squall line of thunderstorms. While menacing in appearance, shelf clouds are not tornadoes or wall clouds.

What you're seeing in a shelf cloud is the boundary between a downdraft and updraft of a thunderstorm or line of thunderstorms.

Rain-chilled air descends in a thunderstorm's downdraft, then spreads laterally when reaching Earth's surface. Warmer, more moist air is lifted at the leading edge, or gust front, of this rain-cooled air. When this warm, moist air condenses, you see the shelf cloud.

As the shelf cloud passes, you feel an abrupt shift in wind direction and increased wind speed, followed within minutes by heavy rain or hail. Wind gusts once the shelf cloud has passed may be quite strong, causing downed trees, tree limbs and power outages.

Unlike a shelf cloud, the roll cloud is detached from its parent thunderstorm(s). Either the gust front surged well away from the parent thunderstorm(s), or the thunderstorm(s) may have fizzled, leaving this remnant roll cloud.

Advancing cold fronts have also triggered roll clouds on occasion. 

Thunderstorm Basics

"Only a small fraction (less than 1 percent) of these storms is classified as severe, producing large hail 3/4 inch in diameter or larger and/or strong downburst wind gusts of 58 miles an hour (50 knots) or greater. A small fraction of the severe storms produce tornadoes.”"must have three conditions present in order to form. The first necessary condition is moisture in the lower to mid levels of the atmosphere. As air rises in a thunderstorm updraft, moisture condenses into small water drops which form clouds (and eventually precipitation). When the moisture condenses, heat is released into the air, making it warmer and less dense than its surroundings. The added heat allows the air in the updraft to continue rising. The second necessary condition is instability. If the airmass is unstable, air which is pushed upward by some force will continue upward. An unstable airmass usually contains relatively warm (usually moist) air near the earth's surface and relatively cold (usually dry) air in the mid and upper levels of the atmosphere. As the low-level air rises in an updraft, it becomes less dense than the surrounding air and continues to rise. This process is often augmented by added heat due to condensation as discussed above. The air will continue to move upward until it becomes colder and more dense than its surroundings. The third necessary condition is a source of lift. Lift is a mechanism for starting an updraft in a moist, unstable airmass. The lifting source can take on several forms. The most common source is called differential heating. As the sun heats the earth's surface, portions of the surface (and the air just above the surface) will warm more readily than nearby areas. These "warm pockets" are less dense than the surrounding air and will rise.”

"All thunderstorms, whether or not they become severe, progress through a life cycle which may be divided into three main stages. The developing stage, called the cumulus or towering cumulus stage, is characterized by updraft . As the updraft develops, precipitation is produced in the upper portions of the storm. As the precipitation begins to fall out of the storm, a downdraft is initiated. At this time, the storm enters its mature stage. The mature stage is marked by a co-existence of updraft and downdraft within the storm. When the downdraft and rain-cooled air reach the ground, the rain-cooled air spreads out along the ground and forms the gust front. Usually the winds associated with the gust front are not severe, but in extreme cases, a downburst can develop and produce severe wind gusts.”"Eventually, a large amount of precipitation is produced and the storm becomes dominated by downdraft. At the ground, the gust front moves out a long distance from the storm and cuts off the storm's inflow. This begins the dissipating stage of the thunderstorm. Even though this thunderstorm has dissipated, its gust front may trigger new thunderstorms as it lifts warm, moist, unstable air.”
"The amount of vertical wind shear in the storm's environment is critical in determining what type of storm will form. Vertical wind shear is defined as a change in wind direction or speed with height. If the amount of vertical wind shear is low (little change in wind speed or direction), then multicellular storms with short-lived updrafts will be favored. Low values of vertical wind shear result in weak inflow to a storm. Because the inflow is weak, the outflow from the rainy downdraft area will push the gust front out away from the storm. This, in turn, will cut off the storm's source of warm, moist air, resulting in a storm with short-“

"As the vertical wind shear increases, storms with longer lived updrafts will be favored. Stronger vertical wind shear results in stronger inflow to the storm. The gust front will be "held" close to the storm, and the storm will have access to the source of warm, moist air for a much longer time. As a result, the storm's updraft will tend to last longer when the environment has strong vertical wind shear. Precipitation will tend to fall down-wind from the updraft rather than through the updraft. This enables the updraft to continue for relatively long periods of time. Closely related to the concept of vertical wind shear is the veering of the wind with height in the lowest mile or so of the atmosphere. Veering is defined as a clockwise turning of the wind direction as we move up through the atmosphere. It is possible to make a rough check of veering winds while spotting. If there are two layers of clouds in the lower levels of the atmosphere, look closely at the directions in which the cloud layers are moving. If the direction turns clockwise between the lower and upper layers, then veering is present.”

- NOAA Advanced Spotter Guide

Tornadoes in Colorado June 2014

June 8, 2014 Mountain Tornado

FAIRPLAY, Colo. — A tornado was spotted in the mountain town of Fairplay Sunday morning.

FOX31 Denver viewer Maureen Stewart sent us a photo of the twister about two miles south of the town around 11 a.m.

At this time, Park County Communications received several reports of a tornado on the ground moving northeast in the area of Black Mountain.

The twister lasted about five minutes. There have been reports of injuries or damage, according to Park County officials.

There was no tornado warnings or advisories for that area at the time.

Viewers also sent us photos of funnel clouds near Lake George to the south and east of Fairplay.

Shortly before 12:30 p.m. Sunday, another tornado was reported just north of the Eleven Mile State Park, heading northeast toward Lake George.

Park County Communications said a reverse 911 call was sent out to residents within 30 miles of the reported location. The tornado was reportedly moving at 10 to 15 miles per hour.

During this same time frame, a funnel cloud formation was reported in the Fairplay area, but this second Fairplay tornado did not touch down.

Sheriff Wegener said a third reported tornado touched down in Lake George at about 12:39 p.m. The tornado hit the Lake George Cabins and RV Park, damaging six trailer homes.

Forest Road 271 closed due to the weather, and Forest Roads 200 and 205 were impassable in some places.

The Storm Prediction Center reported that a total of eight tornadoes touched down in Colorado Sunday.

Tornadoes in Colorado’s high country are extremely rare.  The National Weather Servicesays 95 percent of Colorado tornadoes occur along and east of interstate 25 where heat and moisture in the lower atmosphere are often more abundant.

Fairplay is about two hours from Denver in Park County.