General August Weather

[snow101]

A cooler, unsettled start to August looking possible.

[Chris W]

Looking full-on wintry for the first week at least, a large blocking high in the Australian bight directing strong southerlies at us, starting tomorrow. Bring on actual winter.

[Cyclone Tracy]

Biggest storm system on earth will sit just south of Macquarie Island on Saturday afternoon as part of the overall cold wave. The polar cyclone is projecting to go into the 920's hPa with a wrap around SW sling shot of brutal cold air. One to watch around the 4th.

[spwill]

Looks like Southland and South Otago in the firing line for low level snow on Sunday, flow direction should keep it mostly down there.

[snowchaser01]

Certainly some cold numbers being pushed out for the first weekend of August. Cold enough for near sea level snow showers in Canterbury. Very WSW flow though so any showers will be few and far between.

[Cyclone Tracy]

Models (over 100) are starting to eye off a significant sudden stratospheric warming event over Antarctica in mid August. EC ensemble is resembling levels from the 2002 event which occurred in late winter and spring of that year. This will get high scrutiny from meteorologist's globally if this comes off like the EC ensemble is suggesting.

[Bradley]

Models (over 100) are starting to eye off a significant sudden stratospheric warming event over Antarctica in mid August. EC ensemble is resembling levels from the 2002 event which occurred in late winter and spring of that year. This will get high scrutiny from meteorologist's globally if this comes off like the EC ensemble is suggesting.

That combined with a very negative AAO could be a recipee for something quite substantial CT?

[TonyT]

Models (over 100) are starting to eye off a significant sudden stratospheric warming event over Antarctica in mid August. EC ensemble is resembling levels from the 2002 event which occurred in late winter and spring of that year. This will get high scrutiny from meteorologist's globally if this comes off like the EC ensemble is suggesting.

September 2002 (as the SSW was developing) had very strong westerly airflows - wet in the west, dry, sunny and warm in the east. October 2002 (when the downstream effects of the SSW were being felt) was the coldest in nearly 20 years, with frequent cold outbreaks, record spring frosts, but drier and sunnier.

[Cyclone Tracy]

The negative AAO (SAM) has more clarity and certainty and is literally falling off the cliff in the next 7 days. Short and medium term model outputs for the southern hemisphere are about to become quite spooked I would say.

The SSW event if it comes off (EC ensemble version) is almost unprecedented at that scale of warming in winter. As Tony's timeline suggests, the impact would be September and could be significant going on the 2002 example. This one is earlier though, so its going to be fascinating to watch it unfold if it verifies.

[Bradley]

The negative AAO (SAM) has more clarity and certainty and is literally falling off the cliff in the next 7 days. Short and medium term model outputs for the southern hemisphere are about to become quite spooked I would say.

The SSW event if it comes off (EC ensemble version) is almost unprecedented at that scale of warming in winter. As Tony's timeline suggests, the impact would be September and could be significant going on the 2002 example. This one is earlier though, so its going to be fascinating to watch it unfold if it verifies.

The most obvious comparison would be the 19th September 2005 events with half a foot of snow for the city and a max of 5C, perhaps something similar would be on the cards and if it occurs in early September then something even more extreme perhaps...definitely something to keep an eye on in the coming 4-6 weeks

[mikestormchaser]

The next cold system is the one to watch on sunday.
Thats got potential for low level snow in the south but as already mentioned it is WSW which doesn't favour Canterbury. One to watch anyway.

[snowchaser01]

The next cold system is the one to watch on sunday.
Thats got potential for low level snow in the south but as already mentioned it is WSW which doesn't favour Canterbury. One to watch anyway.

THK levels are way down around 518 even this far north so one would say if we get any precip it will be very wintry. As you say, one to watch.

[Chris W]

Dare say I'd take a single snowflake falling at sea level in Chch and be happy with that

[TonyT]

The next cold system is the one to watch on sunday.
Thats got potential for low level snow in the south but as already mentioned it is WSW which doesn't favour Canterbury. One to watch anyway.

Airflow over Canty is actually progged to be light easterly on Sunday with the developing trough. Hence the risk of snow to low levels.

[snowchaser01]

The next cold system is the one to watch on sunday.
Thats got potential for low level snow in the south but as already mentioned it is WSW which doesn't favour Canterbury. One to watch anyway.

Airflow over Canty is actually progged to be light easterly on Sunday with the developing trough. Hence the risk of snow to low levels.

What do you reckon the chance of sea level is Tony? Excuse my ignorance but will a light easterly create an advection element or something?

[TonyT]

Airflow over Canty is actually progged to be light easterly on Sunday with the developing trough. Hence the risk of snow to low levels.

What do you reckon the chance of sea level is Tony? Excuse my ignorance but will a light easterly create an advection element or something?

50/50. Easterly is neither here nor there, it just signifies the presence of the trough developing above. Dynamics comes into play, uplift, boom!

[snowchaser01]

What do you reckon the chance of sea level is Tony? Excuse my ignorance but will a light easterly create an advection element or something?

50/50. Easterly is neither here nor there, it just signifies the presence of the trough developing above. Dynamics comes into play, uplift, boom!

Intriguing. I can't see much (if any) moisture due to to it being so WSW... But I guess an easterly flow changes something.

[TonyT]

Intriguing. I can't see much (if any) moisture due to to it being so WSW... But I guess an easterly flow changes something.

Indeed, not much moisture at all. Its not exactly going to be a blizzard. But a developing short wave trough over the top in an unstable southwest airflow usually produces something.

[NZ Thunderstorm Soc]

Dynamics comes into play, uplift, boom!

It would do if it was in the middle of summer

[TonyT]

Dynamics comes into play, uplift, boom!

It would do if it was in the middle of summer

Ok, so boom was a poor choice of word.

[Richard]

It would do if it was in the middle of summer

Ok, so boom was a poor choice of word.

yer, maybe a crackle or two, and even the odd pop

[snowchaser01]

If we don't see snow flakes falling in Christchurch during the next 10 days... I don't think we ever will...

[mikestormchaser]

I see what you mean Tony. The winds are pointing more ENE on sunday.Most of the moisture looks like the early hours of Sunday though.
But at the same time here is the 850mb temps at 3am sunday. I dunno im more a thunderstorm enthusiast myself so i find it harder to know what im looking at when it comes to snow events
Pretty cold looking though

[snowchaser01]

Seems as if MetService 3 day maps agree with you Tony... how about that for a snow line!!

[Bradley]

Seems as if MetService 3 day maps agree with you Tony... how about that for a snow line!!

And yet on both Chch and Darfield forecasts for Sunday they both only say snow to 500m, perhaps they will be updated today sometime to reflect their own data?