Convective Check in 2 Supercells.

Overview.

Created from a highly localised vortex these unmistakable cloud structures Supercells are likely created as part of summer low pressure systems and mid latitude storms but can also appear outside summer. They are known as rotating updrafts OR mesocyclones and can be common in places affected by summer weather if the correct ingredients are in place (CAPE/SBCAPE) and Speed shear/Directional shear and other weather mechanisms. There very presence signifies the sight of a highly localised rotating storm and are short lived from 1-7 hrs duration producing typical storm events sometimes severe. Supercells tend to operate not as part of a organised line but sprout up individually and are short lived up to 7 hours in duration. They are uncommon all year but given the correct time of year (Summer) and circumstances (Ground Heating/Convection/Directional Wind shear/Speed shear) Supercells may make there presence known over a week to weeks to a few months duration of irregular appearances in one given region.

There are 3 kinds of Types for the Supercell Family.

• The Classic Supercell (Normal type a hook echo on the doppler radar).
• A HP supercell (High Precipitation).
• Low Precipitation Mode Supercell (LP).

Normal Precipitation supercells may be found for example in Wide grassy expanses on the Rainfade side of Mountain chains, Low Precipitation storms in dry desert environments and HP supercells in places like Maritime environments or Hot Humid environments that provide the water molecules to saturate and warm the updraft usually in summers AND speed shear to tilt the storms structure.

The ingredients for the storm supercell formation for the Classic and HP type (More rain production) is instability (CAPE/SBCAPE in the mid and high levels) and Moisture input to create warmed water molecules rising into a Directional and Speed Wind Sheared environment that cools the parcel of water molecules on the way upwards. This then will saturate the air column of the storm. On the ground this instability can also be then helped greatly by Summer Heating/High Humidity ingested into the mid and high levels of the storm where mostly CAPE/SBCAPE happen. Moist air molecules travel into the supercell via a transport mechanism called low level winds and are then consumed into the supercell storm system. The storms longevitiy is aided by Speed shear that tilts the storms structure and this works in tandem with all other supercell factors to create this storm type.

The LP Supercell is so named when instability in the area of the storm forms the supercell but the storm is drawing in Dry air molecules (Lack of moisture and very Low to none precipitation) these are synonomous with Hail Production.

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First Glimpse The Classic supercell.

A classic supercell appears over the praires with the distinctive rotating updraft and mesocyclone (Taken south of the system in the northern hemisphere).

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Inside the mesocyclone 1 Rotating updraft.

We are seeing in the image of this south view of the mesocyclone the invisible effects of the pressure gradient and in the updraft strong directional wind shear. It is Speed Wind shear that will help to tilt the storms structure whilst directional wind shear creates a warm strong updraft that in turn seperates from the cold downdraft and remembering from our former lesson in Convective Check In 1 this seperate updraft and downdraft helps to sustain the storms lifecycle (shorter lived singular storm engine). This process then creates the unmistakable shape of the mesocyclone and the rotating updraft that is a result of this swirling storm and is highly indicative of a supercell. With the warm strong rotating updraft/seperate cool downdraft put in place by speed shear a classic supercell begins formation and quickly may establish the storms presence for up to 7 hours controlled by the 500mb steering winds to move the storm in a given direction that will normally veer to the right when matured. This may mean a east-north east pathway from the storms origin (Low pressure center) in the northern hemisphere and adverse weather can be expected on this path and for the duration of the storms existence including the possibility of strong tornado production.

The upper image shows also the Anvil of the storm in the upper region and the Overshooting tops held central to the upper storm as the updraft here projects clouds upwards. Finally the region of the beginning of the upper outflow in the storm is shown to the south west of the storm where the cold front resides at surface when the storm is viewed from the south as above.

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Inside the mesocyclone 2 Hail Production.

The effects of the supercell updraft/downdraft in this occasion on the ground can be felt from Hail Production of the small, medium, and large type with Larger hail encountered nearer the warm updraft and smaller hail nearer the rain output area. Hail production can sometimes if the correct factors are in place produce hail the size of softballs as the rotating updraft speeds increase hail size in the updraft area therefore large hailstone production is not uncommon with Supercells this is also true of LP supercells (Desert scenario) where large hailstone production is possible.

Hail production in a super cell spans the 3 types (Classic, HP, LP) and is a hallmark of supercells with the rotating updraft moving rain droplets high enough to freeze the droplets. It is also important to note that Supercell storms do not all have the same Hail production traits and the hail effects differ from Supercell to Supercell. Hail effects may not effect the ground, Hail may melt in the downdraft entirely and increases rain output, or Larger Hail may partially melt in the downdraft shrinking the hail stones felt on the ground. The convective composition of the supercell and what convective composition is in the region before the storms form is what will affect Hail Production to a large degree and the effects felt on the ground.

The factors that combine to promote Hail production and Hail affecting the ground are:

• Hail falling in the downdraft where there is none rain.
• Hail that is produced larger is more likely to reach the ground along with none rain.
• A seperated strong warm updraft and cool dry downdraft.
• The hail downpour swath is seperate from the rain downpour area.
• The above scenarios are more favoured in the LP type supercell.

The factors that combine to promote Melting Hail that increases rain rates to the ground (rain only) are:

• Hail falling in the downdraft area along with rain.
• Hail that is produced smaller encountering warmth in the downdraft and melting.
• Smaller size hail production in the warmer weaker updraft.
• Weak Storms that are do not have a strong rotating updraft to produce large hail (weak rotating updraft) yet rain load to produce heavy downpours as the hail melts in the downdraft.
• Largest hail melting in the rain downpour and shrinking the hail size and increasing rain droplets size and frequency.
• The above factors could be highly favourable for the HP type of supercell.

Large Hail may as we know fall into the Rain Region and may be melted (Highly Likely) and Hail swaths are created when the updraft of the supercell is weakened and/or when the hailstone size overcomes the updraft and then begins falling towards the ground in either the dry or wet state of the storm. Winds may also move small hail away from the Updraft and then a hail swath happens as the density of the individual hail overcomes air buoyancy away from the updraft region.

Finally LP supercells (Low Precipitation) tend to sometimes produce larger hailstones with little to none rain as there is no rainfall to melt hail and dry cold mid to high cloud structures form with a strong warm vertical updraft that ingests moisture from another source (Mid Level winds). LP supercells are adept at times to produce large hail size swaths.

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Hail to the ground.

As a prime example a hail swath is shown above. Hail can be compared to common items in life like Pea Sized, Penny sized, Golf ball sized, Tennis ball sized to determine hail sizing and hail storm swaths can be hazardous to crops, animals, cars, property, aviation, humans in extreme situations. Your best bet in this occasion is to be alert to a supercell location and intended direction and conditions (Forecast) and to stay alert when a supercell is around (Stay notified).

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Tornado/Twisters.

Due to the rotating updraft and mesocyclonic structure of the supercell they are most likely of the convective storm types to produce Tornadoes. Tornadoes are wind funnels that reach from the cloud structure winding down to the ground of sometimes tremendous highly localised vertical rotating strength and Tornadoes (Twisters) can very in strength. They can at there worst create widespread destruction in the Tornadoes path and present many dangers but only in the central infeed and inflow boundary wind region of the wind funnel that feeds the tornado core that can be a few yards wide to up to over a mile wide (rare). Once again it pays to stay on the forecast and heed the early warnings when one is in the area. The corner area of the tornado holds the brunt of the power of a tornado located at the central Base of the Wind Funnel at ground level where the winds flows into the wind funnel. Lastly the inflow boundary of the wind funnel can have powerfully strong wind factors as the wind funnel draws in wind in this area close to the ground. The wind inflow boundary follows a pre-determined path to the center of the tornado from outside the tornado central wind funnel and as such being within this inflow boundary can be highly hazardous.

Lastly the tornado may have a backside windfield that operates in the opposite direction going towards the ground and as this wind meets the ground gusts will spread out from the backside area of the tornado. Tornado formation is most favorable when the cloud base of the supercell is closer to the ground. LP supercells tend to not sprout that strong a version of tornadoes as the cloud base is higher but it pays to be alert around a LP supercell if they are in your region.

Tornado production from supercells are estimated to happen in around 30% of Supercell Storms so paying attention to there presence, staying informed and being aware of the on ground situation becomes important should a Supercell be in the area and therefore prepare for emergency action early not later.

Doopler/Hook Echo Detection.

Here we see the Classic Signature of a supercell captured by Doppler Radar and is known as a Hook echo (center of image) this in turn identifies this storm as a classic Supercell. This is resembled by a colorful pendent shape with a distinct kink on the end that reveals the existance of a Mesocyclone at work (center of image). The Bright Red and Orange colors signify a thunderstorm in action as this supercell is well underway straight out of the oven as they say. Doppler radar can be handy to locate supercells but need constant monitoring to trace where they are and overall development. The environment in a area before a storm mechanism arrives may determine if supercells may form as in CAPE/SBCAPE availability and High Surface Humidity in tandem with the directional/speed sheared wind environment. Last in the ingredients is Hot Summer Ground Heating, if a localised cloud blanket breaks apart in summer this could be a sign something is well underway. Classic supercells sometimes are better resembled using Doppler radar then other types.

HP supercell sighting.

In the above image we see a High Precipitation Mesocyclone at work (HP supercell) and these storms have the standard attributes of the Supercell with the exception that they produce a very heavy blanket of downpours in the rain output area and a possible mix of small hail. As the air column becomes rain loaded this then can highly reduce visibility on the ground and obscure tornado sighting and identification when this happens this is known as a rain wrapped storm as the updraft area becomes obscured by heavy rains that wrap around the supercell storm structure.

On a doppler radar scan one would identify them with the bright red/orange/light yellow dbz signature but this takes advanced skill to master.

HP supercells are common in summers in areas with high surface humidity going up to 500mb (rain loading) and there weather effects outside the Tornado production domain includes weather factors to be made aware of. HP supercells can possibly bring therefore

1. Possible Range of tornados including strong ones.
2. Heavy rains and flash flooding especially in gulleys and lowlands.
3. Possible for Hail production.
4. Strong winds.

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Upper Level Winds/Non-Summer.

When we discussed the formation of the supercell storms there was mentioned that these are highly active in summer heating and convective situations but there are occasions where they may happen outside summer.

In the Northern Hemisphere this situation will arise at the Jet Stream level (30,000 feet) in a pattern known as a negative tilted upper level trough. In this situation the shape of the jetstream field resembles a north west to south east tilted orientation with a polar blast addition at the Jetstream.

This jet stream pattern is conductive to possibly produce an outbreak of supercells only if the correct ingredients are in place in the regions storm producing environment as we spoke of along with the presence of the negative tilted jet stream trough we are seeing above and applies to the northern hemisphere weather patterns outside summer. Lastly a jetstreak is shown in the jetstream that is an amplified area in the Jet stream that has stronger then normal upper level winds and this also helps in the production of severe storm creation in a non winter scenario. Lastly to add extra detection of tornado production in this scenario a measure called "Helicity" can be used to forecast possible tornado creation in a region in combination with the supercells inputs and the above Jet wind pattern.

Once again it is the best bet to follow your local forecasts and stay alert.

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Vorticity and the Parent storm.

In this section we discuss in the supercell creation forefront the possibility that supercells are created/spawned within the mid-latitude storm system. This is entirely plausible if the Mid Latitude storm encounters the necessary elements to create and fuel the supercell such that a supercell will appear for a duration as long as the updraft and downdraft remain seperated as already discussed.

Vorticity represents the spinning-movement and direction of large masses of molecules within a wind field and movement-directional energy for this larger vortex and for the supercell holds prominence in the creation and sustaining of them essentially being a highly localised vortex (supercell) within a larger one (Mid Latitude storm) for the Mid Latitude storm as shown above. As Mid Latitude storms affect the synoptic scale (larger surface areas) vorticity aids in the moving of large masses of air of two differing types cold-warm as shown above. Lastly in the Northern Hemisphere the vorticity direction for the above mid latitude storm always moves anti-clockwise that in turn signals a low pressure system is evident.

The weather factors that influence and create a mid latitude storm in this scenario are typical of all mid latitude storms being.

1. A low pressure center.
2. A cold front eminating to the south west of the storm at this stage of the storms creation.
3. A warm front that places to the East of the low pressure center.
4. Warm moist air entering to the south of the system from a moisture source.
5. Cold air to the north - nth west of the system entering to the system.
6. The unmistakable wind field rotating in a anti clockwise direction on the synoptic scale.

In this section we discuss in the supercell creation forefront the possibility that supercells are created/spawned within the mid-latitude storm system as shown by the doppler radar ideal. This is entirely plausible if the Mid Latitude storm encounters the necessary convective elements we have explained to create and fuel the supercell such that a supercell will appear for a duration as long as the updraft and downdraft remain seperated as already discussed. The weather factors that influence and create a mid latitude storm in this scenario are typical of all mid latitude storms being.

In the above image this shows how a mid latitude storm appears on a surface pressure chart, this is possible supercells may form in the storm cells area depicted with enough warm moisture and convective fuel and directional/speed wind shear in the secondary air vortex to sustain the supercell structure in this idealised situation as the supercell sub structure forms in the rotational field of the main storm. The Warm front and moist inflow sustains the inflow of the child storm (Supercell) whilst the cold front will promote the outflow area of the child storm the sign that speed shear is at work. The typical movement of Mid Latitude storms in the northern hemisphere is west to east movements but check your local forecasting charts to confirm. Mid latitude storms are ideal in winter weather to produce winter weather and are so named as they appear in the mid latitude bands in all weather.

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The shear factor.

There are two important wind factors that are part of the creation of and sustaining of a supercell being Directional shear and Speed shear. In the above image the effects of directional wind shear is shown on the right that is vital to creating and sustaining the supercell as in each of the vertical areas of the storm vertical structure wind direction changes creating the highly localised mesocyclone. On the Left of the image lastly represents Speed shear that has wind speeds that travel straight but at each individual level in the air column the wind speed increases gradually and creates a tilt in the storms structure to seperate the warm rotating updraft and cooler downdraft necessary for stormy weather supercells creation and sustaining. Thus the two wind shear factors must be present for the supercell storm to announce a presence in the area.

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Supercell Ingredients 1.

These are the ingredients that are essential to creating a supercell with each ingredient having a scientific measure that quantifies the storm ingredient. This quantification is a measurement and the ingredient and measurement combine in the supercells environment to determine what type of supercell is created, what is within the supercell and how the supercell is affected over time.

• Instability Increased heating at surface (Hot Summers) and a cooler mid (700mb/500mb) to jet level (300mb). SBCAPE/MUCAPE/CAPE are scientific terms to help quantify Instability in a regions environment.
• Moisture An available source of low level input will feed saturated air molecules into the supercell represented at the highest range of measurement by High Dewpoints of 75% or more. The higher the dewpoint the more saturation of the storm will take place (HP supercell). 75% dewpoint represents a invisible state that water molecules are packed into a parcel of air.
• Increased Surface warming will create in the Planetary Boundary Layer expanded air (warm and less dense) that rises and is essential to supercell creation. The scientific measurement is PBL temperature.
• A strong Low Level Jet carrying adequate moisture infeed will assist supercell creation. Winds are measured in knots this scientific measurement is Advection at 850mb.
• Directional shear from surface to 3100m high in the storm height represents the change of wind direction in relation to height change intervals to 3100m high these are picked up in Hodographs. Best explained by wind changing direction at intervals when looking at a imaginary vertical line from the ground to 3100m height.
• Speed shear is straight directional winds that increase at different intervals of the imaginary vertical line except the imaginary line is higher then 3100m from the ground. The Highest interval of Speed shear is the highest straight wind force. Linked strongly to Storm tilt.
• Jet stream wind speeds and pattern can influence Supercell creation including jet stream location and wind pattern type (negative tilt). Stream patterns are controlled by the Known Collected Pattern List and Speeds in knots and Wind direction.
• Vorticity is the twisting of a large area of air mass and Positive Vorticity in the Northern Hemisphere represents Low Pressure (Anti clockwise spin). Vorticity is measured in Rotations per second.

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Supercell Ingredients 2.

To quantify how what we have spoken of in relation to the Supercells inputs and how this determines mesocyclone creation to a large degree refer to the above chart. If all the factors are present that contribute to the supercells creation are measured and then plotted on a example very hot and humid day then this storm is going to contain Very Strong Convection/Highest Rainfall/Tornado Production/Hail/Strong Winds as we trace Parcel 5 into the top percentile of the storm factor graph. Then based of what we are taught this then is a severe HP supercell and a forecast is sure to offer a form of safety.

This graph is a graphical representation of how all the ingredients combine in an area to affect the end result of the supercell from the ingredients of the previous storm section.

We then see the ingredients inputs and there measurement strongly correlate to the weather that can be expected from the storm Supercell and if one may develop.

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Fronts.

Weather fronts accompany the Mid Latitude storm and are included in combination with Supercells if the weather and conditions are ripe. They form part of the Main Storm pattern abuting into the low pressure centre and bring the following conditions according to the three main front types:

• Cold Fronts will bring steep cloud banks along the cold front boundary that sometimes move quick at surface. The cold front boundary seperates cool air masses from warmer airmasses as the Main Storm takes place so is the cooler side of the common extratropical storm pattern. For the supercell also is the cooler downdraft region of the secondary vortex. Rain happens within the steep cloud bank area of the front.
• Stationary fronts where two fronts combine into one with a warm front side to the boundary and a cold front side to the same boundary. Are known to hold in place for a time as both front types lack the strength to overpower the other. They may meander along coastal areas and hold weather there (rain).
• Warm fronts are a shallower incline that covers a wider distance and forms the inflow to the warmer ingestion of moisture into the main storm warm front boundary. They give cloud- possible drizzle along a wide area of the front and also is the area of the warm moisture infeed into the updraft of a supercell if one should decide to develop. Warm fronts seperate the two air masses cold-warm and the direction of the symbol shows the area of the fronts direction on a surface pressure chart. Therefore we see in a extratropical storm the warm front serves the purpose of infeeding warm moist air into the main storm system where this moist warm air meets a cooler air mass.

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