General July Weather

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Cyclone Tracy
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General July Weather

Unread post by Cyclone Tracy »

2 cents worth. Significant cold signals are appearing for July.

- Sister lower stratospheric vortex's appearing on all models in early July.
- Coupling down effect then distorts and weakens the tropospheric polar vortex structure. Polar jet will be cut loose into the mid latitudes.
- SAM (AAO) index is now falling off the cliff on most GEFS ensemble members. Some near negative 4 in mid July.

Rug up :smile:
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Chris W
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Re: General July Weather

Unread post by Chris W »

Hadn't seen that but there were some signs the other day of the vortex starting to distort somewhat. Might look and post in the strat thread later. If the tropospheric modelling is looking at cold signals in July as a result that would be a reasonably short lag time?
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Re: General July Weather

Unread post by Cyclone Tracy »

Chris W wrote: Mon 29/06/2020 14:46 Hadn't seen that but there were some signs the other day of the vortex starting to distort somewhat. Might look and post in the strat thread later. If the tropospheric modelling is looking at cold signals in July as a result that would be a reasonably short lag time?
The polar vortex is displaced around 2 - 5 July. You will see that GFS 18Z is now incorporating a significant propagating Rossby wave into the NZ region medium term. At the moment it's a signal, finer details still unknown.
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Re: General July Weather

Unread post by TonyT »

The weekend of July 11/12 is starting to shape up for a significant cold impact. Time will tell if its a snow to low levels job or too light on the moisture. The following week will probably see -10deg or colder frosts for the inland South Island under intense high pressure.
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Re: General July Weather

Unread post by Chris W »

Quite a lot of rain around before that as well, doesn't look settled early-mid month at least.
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Re: General July Weather

Unread post by NZstorm »

Ruapehu district gets its first snow fall of the year tomorrow into Thursday.
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Re: General July Weather

Unread post by Bradley »

TonyT wrote: Mon 29/06/2020 21:11 The weekend of July 11/12 is starting to shape up for a significant cold impact. Time will tell if its a snow to low levels job or too light on the moisture. The following week will probably see -10deg or colder frosts for the inland South Island under intense high pressure.
Thanks Tony thought that isn't like you to talk about events so far out, is there something in the models that is leading you to think that it is a possibility? Negative AAO combined with a favourable phase of the MJO perhaps?
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Re: General July Weather

Unread post by TonyT »

Bradley wrote: Tue 30/06/2020 09:46
TonyT wrote: Mon 29/06/2020 21:11 The weekend of July 11/12 is starting to shape up for a significant cold impact. Time will tell if its a snow to low levels job or too light on the moisture. The following week will probably see -10deg or colder frosts for the inland South Island under intense high pressure.
Thanks Tony thought that isn't like you to talk about events so far out, is there something in the models that is leading you to think that it is a possibility? Negative AAO combined with a favourable phase of the MJO perhaps?
Well I have been quite vague, deliberately!

MJO is spiking into 2 and expected to be declining in 3 by then. So that is supportive of the idea (well lets put it this way, you wouldn't put money on a mild N airflow with that MJO pattern). But really its just something which has been in the longer range modelling for some time (so consistency is a factor) and backed by the posts above - in a time when meridional flow is dominant over zonal and the polar vortex is wobbly (not unusual) then a leak of cold air onto the country is likely, but when?. Those dates just fit with what the longer term modelling is saying.
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Re: General July Weather

Unread post by Chris W »

The signal for cold, stormy weather into July is pretty strong now, and the SAM/AAO is tanking fast! I am not sure that even the super ridge can halt this :p
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Re: General July Weather

Unread post by TonyT »

Chris W wrote: Tue 30/06/2020 10:32 The signal for cold, stormy weather into July is pretty strong now, and the SAM/AAO is tanking fast! I am not sure that even the super ridge can halt this :p
I'm not convinced. The anticyclone which will settle into the cold air after 11th/12th could be hard to budge till the end of the month.
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Re: General July Weather

Unread post by Razor »

TonyT wrote: Tue 30/06/2020 11:23
Chris W wrote: Tue 30/06/2020 10:32 The signal for cold, stormy weather into July is pretty strong now, and the SAM/AAO is tanking fast! I am not sure that even the super ridge can halt this :p
I'm not convinced. The anticyclone which will settle into the cold air after 11th/12th could be hard to budge till the end of the month.
I hope you are right Tony, planning a school hols trip up the West coast that week ;)
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Re: General July Weather

Unread post by Chris W »

TonyT wrote: Tue 30/06/2020 11:23
Chris W wrote: Tue 30/06/2020 10:32 The signal for cold, stormy weather into July is pretty strong now, and the SAM/AAO is tanking fast! I am not sure that even the super ridge can halt this :p
I'm not convinced. The anticyclone which will settle into the cold air after 11th/12th could be hard to budge till the end of the month.
Guess I'm talking mostly til the middle of the month. I haven't studied the stratosphere as much lately (model fatigue and vortex looked pretty darn strong) so I wasn't sure what would happen later in the month. Guessing the vortex distortion could come into play late-month?
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Re: General June Weather

Unread post by Awhituobs »

only 8.7c with a fresh wind blowing
(i.e so windchill makes it much colder)

thats a big change of 12c lows we were getting
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Re: General July Weather

Unread post by Chris W »

3C all the way to Amberley this morning, some very sharp gusts too.
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Re: General July Weather

Unread post by David »

Coldest morning of the year in Howick so far, 3.3C. Was noticeably warmer than that arriving in the city about 7.30, felt more like 8C.
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Re: General June Weather

Unread post by Awhituobs »

woa I see Ricky got down to 5.6c with still a bit of a breeze
will be a shock for aucklanders this morning
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Re: General June Weather

Unread post by Awhituobs »

even worse you are currently at 3.4c David
thats colder than Invercargil is at the moment
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Re: General July Weather

Unread post by NZstorm »

Met Service have a heavy snow warning out for the central North Island with snow to 500m. I can see the SH1 Desert Road closing by the end of the day.
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Re: General July Weather

Unread post by Richard »

1.4mm overnight, not looking like much more than that from this system. A light dusting around the hills which looks about what the MetS had forecast
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Re: General July Weather

Unread post by Chris W »

Snow to approx 7-800m on the Seaward Kaikouras, quite a lot of it in the gullies at least.

Biting wind today in Kaikoura, feels like temperature of 1C is accurate.
Last edited by Chris W on Wed 01/07/2020 15:22, edited 1 time in total.
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Re: General July Weather

Unread post by JP. »

May have been my eyes deceiving me but I believe I just spotted some snow over towards banks peninsula way
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Re: General July Weather

Unread post by tich »

JP wrote: Wed 01/07/2020 14:01 May have been my eyes deceiving me but I believe I just spotted some snow over towards banks peninsula way
There was a dusting on Mt Herbert yesterday, and it's even colder today so almost certainly some. (non-settling flurries reported on Port hills this morning)
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Re: General July Weather

Unread post by NZ Thunderstorm Soc »

Cold day here to start off the second half of 2020.
A partly cloudy day with only a trace in the rain-gauge, probably from a few spits overnight.
South-westerly winds more so towards the coast, where you see those cold rain showers, out to sea, moving north or NE towards ChCh/BP.
8.7C for today.
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Re: General July Weather

Unread post by Razor »

tich wrote: Wed 01/07/2020 14:05
JP wrote: Wed 01/07/2020 14:01 May have been my eyes deceiving me but I believe I just spotted some snow over towards banks peninsula way
There was a dusting on Mt Herbert yesterday, and it's even colder today so almost certainly some. (non-settling flurries reported on Port hills this morning)
Nothing on Port Hills tonight, nor over the Harbour below the cloud base on Herbert ie 800-900m. Maybe some up there overnight
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Re: General July Weather

Unread post by Awhituobs »

cold heavy rain showers going through the auckland area!
5c here with rain
i.e cold air trapped at the surface with rain showers going over the top of that
we dont get it much colder than that!
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