Queensland ASWA Meeting – Summary

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Australian Severe Weather Association logo

Australian Severe Weather Association

The Australian Severe Weather Association held a meeting this afternoon at Logan North Library. There were five presentations:

  1. Thunderstorms & Instability 101 – Anthony Cornelius
    • This presentation covered the essential ingredients of a thunderstorm:
      • Moisture
      • Instability
      • A trigger
    • Anthony covered the basics of thunderstorm forecasting
      • There’s usually a stable layer of air just above the ground.
      • A trigger pushes air above that layer into unstable air
      • There are several forms of triggers
        • Troughs – elongated areas of low pressure where winds converge and air rises
        • Cold fronts – wedges of cold air that push airmasses ahead of them upwards
        • Mountain ranges – force winds upwards
      • Moisture – Anthony stressed the importance of understanding moisture depth to forecast thunderstorms accurately.
      • Instability – There are numerous different measures of instability in the atmosphere:
        • Lifted Indexes – negative values indicate instability, lower the value more unstable
        • Showater index
        • CAPE – Convective Available Potential Energy, higher numbers indicate more instability
        • Total Totals
        • SWEAT Index
        • SRH
        • EHI
        • SKEW-T charts
    • Do you read the SKEW-T?
      • Anthony spent quite a bit of time explaining the SKEW-T chart.
      • SKEW-T charts plot dew point and temperature against pressure height or altitude.
      • The left hand red line indicates the dew point, while the right hand line indicates temperature.
      • The grey line shows the temperature a parcel of air would drop to as it rose through the atmosphere.
      • The further the temperature line is to the left of the grey standard parcel line the more unstable the air is at that altitude.
      • Lifted Indexes are based on the temperature difference between the standard parcel and the real temperature at the 500mb level.
      • CAPE is based on the entire area between the standard parcel and the temperature line.
      • Anthony covered the definition of a cap or inversion, showed some examples and discussed how it affects rising air.
      • The Dry Adiabatic Lapse Rate, Saturated Adiabatic Lapse Rate and Mixing Ratio lines were overviewed.
      • Anthony discussed why moisture is so important in driving instability. When water vapour condenses to droplets as the air reaches 100% humidity, heat is released. This heat slows the rate at which the air cools, which makes it rise faster.
      • Anthony discussed replotting the standard parcel line and ensuring it is representative of the real atmosphere. BSCH Stormcast can be used to do this, but it’s good to learn to do manually.
    • So if you learn all this is forecasting easy?
      • The answer is no for many reasons:
        • Models may be wrong
        • Small changes in the real atmosphere may make a big difference
        • There’s a lot more to it than just the basics.
  2. Coastal Convective Interactions Experiment – Joshua Soderholm
    • Joshua presented his PhD candidate research project, studying the impact of seabreeze interactions in the intensification of hailstorms in South East Queensland.
    • He is using 17 years of radar, sounding and observation data as well as current new observations.
    • By analysing the tracks of storms over this period he was able to confirm the anecdotal observation of many stormchasers – the Boonah-Beaudesert area is a really a severe storm hotspot. Esk is also another hotspot
    • Sea breeze interactions brought about some of the worst events in South East QLD – the Brisbane tornado, Redcliffe tornado, Brisbane hailstorm and The Gap supercell.
    • Joshua has created a tool called Weathervis, which he has used to analyse 154000 cells, 42000 storm tracks, estimating hail size, automatically producing maps and visualisations. This combines 17 years of data at a 1km resolution.
    • His preliminary results indicate that severe hailstorms are much more common in the Boonah, Beaudesert and Esk areas on sea breeze days.
    • This storm season he is undertaking a field program using the BOM CP2 research radar at Redbank Plains and portable LIDAR and X-Band radar systems to locally analyse severe weather events in the Lockyer Valley area.
  3. Skype Interview with Tim Marshall

    Skype Interview with Tim Marshall

    Interview with Tim Marshall by Justin Noonan

    • This interview was conducted with pioneering stormchaser Tim Marshall from the USA via Skype. Tim has been chasing for 30 years, has a Masters degree in Atmospheric Sciences, has authored several books and founded Storm Track magazine in 1986.
    • Tim Marshall first became interested in storms as a child and after an F4 tornado affected his town he became fascinated with understanding storms.
    • He discussed his surveys of damage caused by tornadoes, including some of the unusual things he has seen such as wooden boards through brick walls.
    • One of the questions was how technology has changed chasing:
      • Old radars just showed storms as blobs
      • Radio media information was hours old
      • There were no updates
      • Storm chasing was mostly visual
      • Communications and data were limited.
    • Another question covered what made the El Reno tornado so bad. This was the tornado that killed well known veteran chaser Tim Samaras.
      • The tornado was cloaked by rain
      • It changed direction, increased in size and sped up – all at once.
    • Tim was asked his opinion on the vast hoards of people chasing storms in the USA. They form a traffic jam around some storms.
      • He expressed his concern about people taking increasingly great risks while chasing, trying to get closer and closer.
    • His one great tip for chasers getting started was to “pay attention to the sky”. It’s easy to be constantly looking at a laptop with loads of data and miss what’s going on in front of you. We now can have too much information.
  4. Bushfire Convective Plume Experiment – Nick McCarthy
    • This was another presentation about a university research project, this time into the affects of instability and other storm ingredients on plumes of smoke from fires, particularly pyrocumulus and pyrocumulonimbus clouds.
    • Pyro* clouds are those clouds produced by rising air and smoke above fires.
    • Nick discussed some of the fire danger indexes, including McArthur Forest Fire Index and their limitations.
    • The same instability and shear that produces storms can produce pyrocumulus.
    • Nick commented that the adage that “fires produce their own weather systems” is not really accurate. They are a product based on the prevailing weather.
    • HIs core research is into the question of how does ambient wind shear, stability and moisture influence fire smoke and ember plumes.
    • He is using similar observation techniques to Joshua Soderholm:
      • Field observations with X-band radar
      • BOM CP2 Research and Mt Stapylton radars
      • Time lapse photometry
      • LIDAR
      • Drones
      • Sondes
      • Automatic Weather Station observations
      • Model forecasting
  5. Thunderstorm Forecasting 201 – Anthony Cornelius
    • Anthony’s second presentation continued on from his first.
    • The focus was the Top 3 Errors people make when forecasting thunderstorms
      • Unbalanced instability and wind shear
        • Shear too strong for instability
        • Not enough shear for instability is more common in Australia
        • The relationship between inflow and outflow strength is important in storm longevity which affects how strong a storm can become.
        • The rain shaft of a storm generates an outflow. This outflow can cut off the essential inflow of warm moist air into the storm then it collapses.
        • Inflow has to be strong enough for a storm not to go woosh and collapse.
        • Higher CAPE indicates higher potential for wind speed.
        • Stronger inflow with a lower CAPE is better than higher CAPE with lower inflow.
        • On high CAPE days storms may come out of nothing and very quickly become severe, but without inflow they may not last long.
        • The best gustfronts occur with good inflow pushing against the outflow.
        • Balanced shear and instability is best.
      • Know your upper levels
        • Upper troughs and upper lows enhance instability. They make air want to rise.
        • Upper ridges make air want to sink.
        • Sinking air supresses updrafts
        • Look for upper cold pools on the 500mb chart.
      • Moisture depth
        • Plotting soundings incorrectly for the moisture depth is a common mistake.
        • Using too high a dew point will inflate the Lifted Index and CAPE values.
        • LI and CAPE values are highly moisture sensitive.
        • The lower levels of the atmosphere will mix in convection, so while it may be moist in the first few hundred metres above the ground, that will mix and dilute in the dry air above.
        • It’s important to visualise this mixing to understand the affects of moisture on the instability potential on the day.
        • Anthony showed a fantastic example from the USA on July 21, 2014. The 4pm CAPE plot showed huge areas of 4000+ CAPE. However only small areas had storms. Why? The areas with the highest instability had a strong cap and shallow moisture depth. That 4000+ CAPE wasn’t real.
Anthony Cornelius presents Thunderstorm Forecasting 201

Anthony Cornelius presents Thunderstorm Forecasting 201

The meeting was a really good overview for anyone with a basic knowledge of storms. It’s possible complete newbies could have been overwhelmed by the information content but there was a lot of very interesting stuff for people of all backgrounds, particularly in the presentations by the university researchers.

Anthony Cornelius had some brilliant presentations as usual. He is always awesome to listen to. Unfortunately due to timing his last presentation was a little compressed, but it still had a lot of value.

During the meeting a supercell storm developed over the Gold Coast Hinterland and moved over North Stradbroke Island, proving to be a bit of a distraction. In the intermission everyone rushed outside to take photos! After the meeting broke up at 4pm, everyone rushed off to chase.

Supercell over North Stradbroke Island

Supercell over North Stradbroke Island

I’d strongly recommend ASWA meetings to anyone who would like to learn more about severe thunderstorms, forecasting and weather observation.