Convective Check in 1 Gust Fronts/Squall Lines/Shelf Clouds.
- Gust Fronts/Squall Lines/Shelf Clouds on the move.
- The storms anvil.
- Gust front 1.
- Gust Front 2.
- Hail.
- Squall Lines.
- The Cold Front.
In our first example we see a reference image we used in this article and the unmistakable formation of a trio of convective anamolies all held within one weather system that has an attached cold front. Cold fronts of this type can sometimes stretch for hundreds of miles but are usually only around 30 miles in length like the one in this article. The trio of convective anomolies found in this reference are.
- The Gust Front.
- A shelf cloud system.
- Squall Lines.
Refer to the following examples below to better understand these weather factors of this thunderstorm and weather variety what to expect and why to be alert around them.
Gust Fronts/Squall Lines/Shelf Clouds on the move.
The system image is the reference system above and contains all 3 convective anomolies and a leading cold front and Heavy Showers. By superimposing the composition of the system we can identify the elements and effects this unique weather system has. The red lines depict warmed air rising up the length of this tremendous system and then feeding into a large cloud anvil and overshooting tops (Updraft) which is placed to the eastern section of the formation. In the area of heavy downpours Cold Air (Magenta Lines) moves towards the ground along the eastern Shelf Cloud and in so doing intense rain droplets/rain sheets/heavy showers are created along the length of the Squall (Outflow) to the west of the Updraft. So the effects for this image will bring Heavy Rains, Darkened clouds, a Cooler environment at the Outflow area of the system along the length of the Squall Line/East of the Shelf Cloud. Lastly the direction of this Trio of weather anomolies is moving west to east as one continual line of convection and weather.
The storms anvil.
In this description above the same weather system has produced in this line of convective weather the pronounced Cloud anvil that abuts West of the Cold Front. Also within the top of the thunderstorm formation are probably a line of overshooting tops that define the upper area of the storms updraft. The system still maintains the Shelf Cloud/Squall Line/Gust front features as discussed in the first section.
In the above image the overshooting tops are further to the east of the image and not that defined.
Gust Front 1.
In the same reference system at the eastern length of the storm sits a windy hazard at surface that will give severe sudden gusts and multi-directional winds powerful enough at times to splinter tree branches. These are known as Gust Fronts and are formed on the eastern length where the cool downdraft from the storm meets the ground. They can stir up leaves/sand and dust from the sudden arrival of gusty winds. Campers Outdoor events and the likes need to be wary to watch for the pre-signs of an arriving Shelf Cloud-Squall Line-Gust Front system like the one used in this reference in order to better prepare.
Gust Front 2.
Lastly we see the end view of the system to better understand in the Reference system Squall Line/Shelf Cloud/Gust Front what is going inside the storm system. At the eastern most length of the system sits the Gust front a area of downwards rushing winds that create the severe surface gusts we have been discussing in this article. So in a recap we can say that the reference system will bring weather factors like
- Heavy quick storm downpours.
- Lightning strikes.
- Sudden arrival of powerful gusty winds even more at the gust front.
- A length of weather up to usually 30 miles or longer.
- Weather travelling in a organised line of convection.
- An attached Cold Front whose triangle point gives the direction of travel (On surface chart).
- Hail production in the updraft/downdraft (If ingredients are in place).
Hail.
Lastly within the system Hail can be present with Hail produced when a powerful updraft lifts warmed water droplets up into the storm along the lengths of the storm front to a atmospheric level (Usually at and above 700mb) where they freeze and then the cold downdraft cools them until they reach the ground as hail stones within the storm downdraft. Hail stones can reach the size of small pebbles to the size of golf balls. The stronger the updraft the larger the hail with also a link to how much saturation of the air parcel is taking place in combination to produce hail. Hail is also one of the hallmarks of strong instability features in the front. Hail does not always manifest in all storm types there is a possibility of this.
The last possibility I am familiar with is Hail production in the Updraft but a warm downdraft in this scenario Hail is produced in the storm but melts at some phase in the downdraft. This is known as melting hail that has the added effect of increasing rainfall in the downdraft. Melting hail can also produce unwanted effects for Aircraft as the hail is only encountered in the mid to upper column of clouds although wise air pilots would avoid the storm altogather.
The squall line.
In our last storm discussion for this Cold Front hidden within the length of the straight line storm is the Squall Line. Squall Lines represent a line of organised thunderstorms where summer heating at the surface heats water molecules rising into a colder upper air column with the end result instability.
The meteorological term for this is High levels of CAPE and CAPE values are used to determine the severity of a storms development in forecasts.
With a cold front moving from an elevated region (mountain) towards the rain shadow side that is the direction the Cold Front is moving down a slope remember in this lesson that the front is moving east. The Cold Front will demonstrate quicker forward moving speed across land on the downslope as Cold Fronts often do.
As the front does so clearing the downslope it will encounter this region of CAPE energy and then the entire CAPE fuelled area and the front and the coriolis effect will create the Squall Line formation aka a summer storm.
Lightning strikes and the other factors discussed above will then become common along the line from the system as CAPE values are high in the Northern Summer and a moisture source to fuel the storm completes the picture of this impressive family of convection the Shelf cloud/Gust Front/Squall Line.
In the above image Doppler radar captures the moment that the system has evolved whereby signals are sent from a base station and then emitted back to the station.
Then the signals are processed to represent different types of precipitation for example here the reds-dark oranges represent thunderstorm signals, the squall line bow is evident, as also the area of melting hail from the doppler radar "signature".
The Cold Front.
In this discussion on Cold Fronts one may always identify them on a Surface Weather chart by there symbols a Blue Line along with multiple blue triangles along the line pointing towards the direction the front is travelling. Cold Fronts usually form in the Mid Latitude bands and are active in Summers/Autumns and Winters. This article discusses the Summer Version of this front type.
The last section of this tremendous system is completed by the discussion on the Cold Front. A cold front represents in this summer storm system a Low Pressure front with origins in the Heights of the mountain ranges to the west. This creates a mountain environment that cools the air along the front and then as the air in a mountain range is less dense naturally lowers the air pressure along the front thus creating a cold front boundary along the length of the mountainous cold front.
As the cold front then travels downslope eastwards-south east the system will encounter a warmer moist air mass east of the front that slides up the colder slope air mass of the cold front when the front meets the area of warm air. A process called frontogenesis is also employed the rotates air masses anti-clockwise in the the northern hemisphere pulls in cold-air in one mass and warm air in the other and the front begins cloud production along the front boundary. Frontogensis is also linked to Front Creation/Intensification. They in turn are also linked to the Mid-Latitude storm pattern.
This will then create a region of vertical cloud embankments along the length of the front (A steeper cloud incline then a warm front) and if the correct elements are in place (Instability/CAPE) cumulonimbus clouds will form along with thunderstorms. These vertical clouds and steeper incline along the cold front are highly indicative of a cloud cold front and is how to identify them.
Cold fronts in this mountain scenario are common in summer but also they are known to form and create thunderstorms in autumn/winter if there is ample CAPE-Instability East of the front although thunderstorms may not be of this type (There are other types). The entire system then combines to bring the conditions we have discussed in this article. This discussion is now well rounded to finalise the features of the Cold Front/Squall Line/Shelf Cloud/Gust Front storm used in this reference.
The very last discussion sees the Front either moving offshore still as a storm boundary line or encountering a region that will weaken the storm. When this happens the storm may slowly dissipate. An example that will weaken a storm is when the downdraft region overtakes the updraft area and the storm can no longer power itself. Lastly Squall Lines like the one we have discussed in this article can last up to 7 hours if the correct ingredients are in place.