A lot of people need to know the risks well ahead of the season unfolding given that there are talks of a good season crop wise with all the rain but also insurers to roof repairers, car yards and property. This season could be quite active storm wise.
Well lets look at the basics of hail is formed. Hail forms in a thunderstorm and is the result of moisture, and moving air. Strong thunderstorms include both air moving up and air moving down inside and around their cores, the taller the storm in the warmer season, the more likely hail is forming.
Each weather system impacts low-level moisture and convective instability as well as the microphysical processes and vertical wind shear, all of which are relevant to hail formation and associated size and rate of distribution. Put that bluntly, each system is different.
Basically the above states, no one can tell you ahead of time when and where it will hail ahead of time, but models and climate analogues can give you a guide to where it is MOST likely to be an issue this season. As I have been doing with my daily forecasts, I give you a range of your hail risks in a format no where else does in Australia, a product that should be available!!!
A broad approach to the hail risk in relation to where you are and how often warnings are issued for large hail in your region in the storms season between October and April.
Lets see how this year pans out.
The CLIMATE DRIVERS are important to the coverage of severe weather throughout the remainder of spring and summer. The current state of play suggests that we will still have the negative Indian Ocean Dipole in place that will be the dominant feature for the Spring and early Summer. This adds more moisture and energy into the atmosphere which can increase the chance of thunderstorms becoming more intense and productive in terms of precipitation.
The other driver to watch through the season is the development of a La Nina phase in the Pacific which at this stage is a 60% chance of occurring through the late Spring and early Summer. That will be a game changer in propelling the severe weather system further into the new year IF it develops.
Finally, if the SAM turns positive then we have more easterly winds that feeds inland troughs, something that we have been seeing in recent times. The final piece of the puzzle has been the presence of colder air in the upper atmosphere and we have this highly unstable, powder keg atmosphere to deal with.
The risk of hail as forecast by this service back in August was above average and remains above average moving forward.
Forecast - Storm Outbreaks for October through April capable of producing large hail. Season 2021/22.
Large hail will feature over the eastern states as per normal this year more frequently than anywhere else in the nation. However, the frequency of large hail warnings associated with thunderstorms this season ahead is elevated due to the climate drivers in place. We have already seen an early warming of the land mass in recent weeks, this air has been transported southeast and east through the nation, and it is just luck so far that a dynamic weather systems has not clashed with the warmer air so far. The area of concern I have regarding the hail risk is that the air is also turning humid early this year over the northern parts of the nation. If that trend continues, not only will we have to contend with the potential of the airmasses clashing, but the addition of higher levels of moisture increases the potential energy available in the atmosphere when the battle ground is set in the spring and summer. There is a lower risk for SA and into WA where seasonal expectations should be met. A higher chance of hail for the food bowl in NSW and northern VIC during the spring this year, especially November and December.
The mitigating factors for hail in these climatic setups is the amount of cloud that will be present across the nation. Now no one can tell you with any great accuracy where the cloud is going to be in November for example but we can look at the temperature profile for the seasons ahead. The seasonal outlook is for a cooler than normal season for November to January.
We can see that large parts of the east will be cooler than normal. We can surmise that is due to cloud cover as well as frequent rainfall. This could put a lid on the atmosphere and stopping the storm risks from being full realised. We have seen time and time again in recent years where the atmosphere is a powder keg and ready to take off, only for the cloud cover to act as a blanket and dampen down the risk profile of severe weather taking off.
So once again, this will not be the last time the events will be present over QLD and NSW. As the nation warms up in the coming weeks and month, the risk of larger hail does spread further south to the remainder of NSW and then VIC and SA into Summer.