2018-10-18 Significant storms around Sydney, Australia

[davenn]

the last couple of days, 17th and 18th Oct have produced some severe thunderstorms in the Sydney basin and surrounding region.
Here's several photos I did from yesterday's activity from my work place in western Sydney ( out towards Penrith)

Intense lightning, heavy rain and surface flooding and some hail

Those second two pic's really show the storm at its menacing worst.

Dave

 

[berkeman]

Wowie. Is this typical, or have you been seeing increases the last few years like North America?

 

[davenn]

Reasonably typical, the last ~ 3 years have been below par for the greater Sydney basin area. most of the best activity has been mainly to the north of us, towards the tropics.
so finally seeing some respectable stuff again … bad for the residents ( me included) and insurance
companies, but great for us storm chasers ( me included).
Tomorrow, Saturday 20th is looking pretty good from the predictions and we are supposed to be
having a local chasers get-together tomorrow nite at home … beer, pizza and lots of good chase
stories and videos tomorrow's settings …….

The first one is the CAPE

1. Convective available potential energy - Wikipedia
   https://en.wikipedia.org/wiki/Convective_available_potential_energy
   
   
   
   
   Overview
   In meteorology, convective available potential energy (CAPE), is the amount of energy a parcel of air would have if lifted a certain distance vertically through the atmosphere. CAPE is effectively the positive buoyancy of an air parcel and is an indicator of atmospheric instability, which makes it very valuable in predicting severe weather. It is a form of fluid instability found in thermally stratified atmospheres in which a colder fluid overlies a warmer one. An air mass will rise if it is less dense than the surrounding air (its buoyant force is greater than its weight). This can create vertically developed clouds due to the rising m…

Anything over 1000 J/kg is good. In those deepest red areas it's over 2000 J/kg. Whilst 2000+ is very good that things really get explosive
and severe lightning storms can be expected.

The next thing we look at is the LI, Lifted Index...…

Lifted index
From Wikipedia, the free encyclopedia

Computer generated Lifted Index field from April 6th, 2009, at 1 pm EDT. Unstable areas are in yellow (slightly) and red (highly) while the stable zone is in blue.
The lifted index (LI) is the temperature difference between the environment Te(p) and an air parcel lifted adiabatically Tp(p) at a given pressure height in the troposphere (lowest layer where most weather occurs) of the atmosphere, usually 500 hPa (mb). The temperature is measured in Celsius. When the value is positive, the atmosphere (at the respective height) is stable and when the value is negative, the atmosphere is unstable.

Determining LI[edit]
LI can be computed using computer algorithms but can also be determined graphically. To do this, generally, the parcel is lifted from the portion of the planetary boundary layer (PBL) that lies below the morning inversion. The air here should be about 60 to 65% RH, which is then lifted along the dry adiabat (see also adiabatic process) to the lifting condensation level (LCL), which is the intersection of that curve with the average mixing ratio in the boundary layer. Once the LCL is found, the parcel is lifted along the moist adiabat to 500 mb. It is then that one finds LI = Te(p) - Tp(p).

LI is generally scaled as follows:

• LI 6 or Greater, Very Stable Conditions
• LI Between 1 and 6 : Stable Conditions, Thunderstorms Not Likely
• LI Between 0 and -2 : Slightly Unstable, Thunderstorms Possible, With Lifting Mechanism (i.e., cold front, daytime heating, ...)
• LI Between -2 and -6 : Unstable, Thunderstorms Likely, Some Severe With Lifting Mechanism
• LI Less Than -6: Very Unstable, Severe Thunderstorms Likely With Lifting Mechanism

Significance to thunderstorms[edit]
The lifted index can be used in thunderstorm forecasting, however, convective available potential energy (CAPE) is considered by most as a superior measurement of instability and is preferred by many meteorologists for convection forecasting.[1] However, LI is easier and faster to determine without using a computer, as determining CAPE requires integration from one level to another.

Note this comment and then look at that chart above

LI Less Than -6: Very Unstable, Severe Thunderstorms Likely With Lifting Mechanism

The LI's in the centre of those purple regions are predicted to get down to -7 to -8 …. VERY unstable
That makes us storm chasers get excited and let out a WooHoo ! haha.

... or have you been seeing increases the last few years like North America?

They ( the professional met office people) keep telling us mere mortals that, with the global warming, we should be expecting more intense weather patterns …
more droughts, and possibly less storms but those that do occur to be more intense.

Wellllllll…… haha …. Australia has always been a place of extremes and the weather/climate is no exception. So far we are not really seeing any of the "out there" extremes that they have been predicting … so who knows ??cheers
Dave