General August Weather

[snowchaser01]

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?

Yes I noticed that too.. strange. Maybe they are just covering their ass because it's a slightly unusual situation? I expect either tonight or tomorrow they might start saying 200m with sleet in chch.

[TonyT]

It all hinges on exactly where the trough will develop, and how much development takes place. Models are all in agreement it will happen, but all quite variable (from model to model, and from run to run) as to exactly where, how much, and therefore what the consequences will be. Suffice to say Sunday has a very wide range of potential weather outcomes at this stage.

[Cyclone Tracy]

On initial GFS, CMC & Icon model 00Z run analysis, they are projecting Monday morning snow possibilities for Wellington and a 528 thickness line to near Auckland.

[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.

Just thinking aloud here, but a key difference between September 2002 and this month is that in 2002 the SSW event occurred at the peak of an active solar cycle, which implies strong jets and an active westerly wind belt at mid latitudes reflecting a well developed "classic" global circulation pattern. As we have all seen lately, the contrast with this season is marked, as we are in the minimum of the weakest solar cycle for more than 100 years, and our jet stream pattern has been all over the place, and our global circulation quite disrupted and "wonky". For this reason I'm not sure that the outcomes of a SSW now would be the same as what we saw in 2002. Major leakage from the polar vortex at this time might be more directed into very deep low pressure tangles or very intense high pressure zones, rather than stronger westerly airflow.

[NZstorm]

700mb temperature chart here for Sunday night. I prefer the 700mb chart for looking at winter convection.

700mb -18C is cold enough for snow at sea level, where the flow is onshore.

[Cyclone Tracy]

Interesting theory Tony.... While being aware of the current solar minimum that's in play, its not my strongest area to provide insightful commentary There is certainly lots of chatter at the moment about it's current and upcoming climate impacts though.

EC 00Z now putting -5c @850 hPa over the lower NI Monday morning with some hints of moisture aloft.

[Chris W]

Just noticed the 3 day MS maps as well, possibly some heavy sea-level snow in North Canterbury on Sunday morning. Possibly down south before that.

Also moderate confidence of SW gales, and low confidence of heavy snow over parts of the weekend for much of the SI. Quite an Outlook!

[snowchaser01]

Just noticed the 3 day MS maps as well, possibly some heavy sea-level snow in North Canterbury on Sunday morning. Possibly down south before that.

Also moderate confidence of SW gales, and low confidence of heavy snow over parts of the weekend for much of the SI. Quite an Outlook!

I think sea level snow for a time on Sunday night from about chch north is possible.

[Chris W]

Started a thread, thought it was time.

[RWood]

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.

October 2002 was most unusual with its combination of cold temperatures and exceptionally high sunshine totals. Looking back, the only other October close to matching it was in 1937 - almost identical mean temp in the 7SS, very slightly less sunny. Would be interesting to see if the circumstances were similar.

[NZ Thunderstorm Soc]

Today is the anniversary of the "Big Blow" of 1975.
I remember it quite well, being stuck in a train heading north from Timaru and only getting as far as Hinds.
Trees, power lines all over the place and even seeing an empty grain silo being blown across a paddock.
It was fine with a nice NW Arch form standing out from the light of the moon.
Apparently it was a significant event with a lot of damage in the forest near Richard's place in the Hurunui.
Eyrewell State forest I think it was.

[RWood]

Today is the anniversary of the "Big Blow" of 1975.
I remember it quite well, being stuck in a train heading north from Timaru and only getting as far as Hinds.
Trees, power lines all over the place and even seeing an empty grain silo being blown across a paddock.
It was fine with a nice NW Arch form standing out from the light of the moon.
Apparently it was a significant event with a lot of damage in the forest near Richard's place in the Hurunui.
Eyrewell State forest I think it was.

Portion of summary for that month:

"August 1975: August was a mild month, and in the South Island it was unusually cloudy and wet. Exceptionally strong north-westerly winds which had commenced in Southland and parts of Otago on 31 July, spread into other eastern districts as far north was Wairarapa on 1 August. Observations at Timaru Aerodrome, Christchurch Airport, Kaikoura Peninsula and the northern end of Lake Wairarapa all indicated winds of at least hurricane force, i.e. averaging at least 64 knots over a period of 10 minutes. Widespread damage was reported, including devastation of large areas of forest, houses deroofed, buildings demolished, and 7 power pylons blown down near the upper Selwyn River in Canterbury. Unusually high gusts included 105 knots on Kaikoura Peninsula, 93 knots at Christchurch Airport, and 92 knots at Eyrewell Forest, north-west of Christchurch. Small local tornadoes caused some damage at Governors Bay on the 1st and at Kaitaia on the 13th."

[cbm]

Dramatic example of marintime air suddenly displacing overnight radiation cooled layer this morning. This PWS across town was on 10 when I was still on 2.

Capture.JPG

[Richard]

Today is the anniversary of the "Big Blow" of 1975.th a lot of damage in the forest near Richard's place in the Hurunui.
Eyrewell State forest I think it was.

Balmoral forest it was called. Yes it was hammered badly, though it should never have been planted there as the alluvial soils were too soft to support trees, they never managed to produce a saw log out of that forest in the 50+years it was in trees

[NZ Thunderstorm Soc]

Eyrewell State forest I think it was.

Balmoral forest it was called. Yes it was hammered badly, though it should never have been planted there as the alluvial soils were too soft to support trees, they never managed to produce a saw log out of that forest in the 50+years it was in trees

Yes, Balmoral forest. I remember in the last days of the branch line to Waiau, driving log trains from there to the port of Timaru for export to Japan.

[Richard]

Did the logs come out of Hanmer John

[Chris W]

Still a dusting of snow on the top 200m of Mt Herbert, incoming dark grey clouds with the southerly change.

GFS and EC both looking at something cold mid-month, long way out but just to note the possibility at this stage.

Southerly just arrived at Lyttelton.

[RWood]

Balmoral forest it was called. Yes it was hammered badly, though it should never have been planted there as the alluvial soils were too soft to support trees, they never managed to produce a saw log out of that forest in the 50+years it was in trees

Yes, Balmoral forest. I remember in the last days of the branch line to Waiau, driving log trains from there to the port of Timaru for export to Japan.

The met report is correct. In fact all 4 state forests suffered significant damage, particularly Eyrewell. Met. were doing observations at all of them at the time, in keeping with the practice of those days.

https://teara.govt.nz/en/photograph/103 ... ell-forest

[NZ Thunderstorm Soc]

Did the logs come out of Hanmer John

There was a siding at Medbury where the logs were loaded onto URL class wagons for the trains that went to Timaru instead of Lyttelton for some apparent reason.

[Richard]

Ok, to avoid getting completely off topic, do you ever remember driving up into this area with snow during 'Aug'

[NZ Thunderstorm Soc]

Ok, to avoid getting completely off topic, do you ever remember driving up into this area with snow during 'Aug'

Rather than get told off by Nev/Tony or other moderator for becoming very much 'off topic', I'll send you a PM

[Razor]

Nothing of note here with the change. Light rain and a moderate breeze. Far from the 100km forecast for this afternoon

[NZ Thunderstorm Soc]

Lovely day in Geraldine today.
Got up to over 15C

[tornado]

Lovely day in Geraldine today.
Got up to over 15C

not nice here in auckland. its been cool and squally showers too.

[talbotmj15]

Looking ahead appears to be more active weather from the south and west. Between 10-16th August. Will watch with interest and far more likely for snow in Canterbury. Current storm was for the most part far to WSW.