Large Rain Event Canterbury and high altitude snow. 29-31st May 2021

[NZ Thunderstorm Soc]

The deluge has started.
Coming onto drizzle here

[mikestormchaser]

Certainly a much needed rain event for Canterbury coming in from tomorrow evening! Very nice to see

The rain is needed, but I'm not sure anyone should be looking forward to this particular event.

Yes can understand that due to being so very dry but in terms of drought breaker its much welcome.
But yes definitely could be some disruption around from sunday onwards.

In queenstown the last few days, a real chill in the air down here with cloudy and cold temperatures today.
Rain from afternoon with fresh snow line on remarkables and cecil peak down around 800m mark.

Back up to Rolleston tomorrow night in time for this rain event

[snowchaser01]

MS appear to be scaling back their rain amounts for ChCh. Good news if that holds

In my opinion it won't hold.

Another update just now and numbers gone through the roof again. 3 day map update also paints a very concerning picture

[Chris W]

UK model tonight is upping the moisture for North Canterbury on Sunday. Prior to that the jet CT is referring to feeds into mid-Canterbury. Porter’s Pass will be a miserable drive!

Updated MetService warning wording (my parentheses added) now refers to Amberley southwards for the red warning, replacing Ashley from earlier. Also there is a warning of severe southeast gales for the west coast that I have omitted:

Heavy Rain Warning (Red)
This rain is expected to cause dangerous river conditions and significant flooding. Slips and floodwaters are likely to disrupt travel, making some roads impassable and possibly isolating communities.

Area: Canterbury south of Amberley
Valid: 44 hours from 3:00pm Saturday to 11:00am Monday
Forecast: Expect 200 to 300mm of rain to accumulate about the Canterbury High Country and foothills during this time, with 80 to 120mm of rain farther east about the Plains and coast. Peak hourly rates of 10 to 20mm/h are expected, especially from later Saturday and during Sunday. Also note, the freezing level is forecast to be around 1400 metres on Saturday, then lifting to around 1800 metres on Sunday, before lowering to 1400 metres again on Monday. Heavy Snow is expected above the freezing level throughout the event, but heavy snow may fall as low as 1000 metres in some places at times, especially on Saturday and on Monday.

Heavy Rain Warning (Orange)
Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous.

Area: Nelson west of Motueka
Valid: 13 hours from 7:00am to 8:00pm Saturday
Forecast: Expect 100 to 130mm of rain to accumulate, especially about the ranges. Peak rates of 20 to 30mm/h, and thunderstorms possible.

Area: Canterbury about and north of Amberley, and Marlborough about and south of Kaikoura
Valid: 50 hours from 1:00pm Saturday to 3:00pm Monday
Forecast: Expect 120 to 200mm of rain. Peak rates of 10 to 20mm/h expected Saturday evening and during Sunday.
Changes: Upgraded to a Warning (Orange)

[snowchaser01]

UK model tonight is upping the moisture for North Canterbury on Sunday. Prior to that the jet CT is referring to feeds into mid-Canterbury. Porter’s Pass will be a miserable drive!

Yes as Tony mentioned earlier... for the first part of the event it is Christchurch southwards, followed by Christchurch northwards. Doesn't pose a pretty picture for city folk with 100mm possible.

[NZ Thunderstorm Soc]

Updated MetService warning wording (my parentheses added) now refers to Amberley southwards for the red warning, replacing Ashley from earlier.

I thought why Ashley? I think they omitted the word River in their warning, as rivers are usual for distinguishing borders for areas like the Rangitata River/Waitaki River being South Canterbury. Ashley is a small township just over the bridge from Rangiora, near Sefton. They have pub and I know some people there.

[Cyclone Tracy]

I just crunched the numbers on 7 global models, UK, GFS, Access, EC, Icon, FR & CMC for the 28 May 12 run for 72 hours. Looked at extremes and the averages. The average is suggesting a major bullseye from Lake Coleridge towards Oxford.

[Razor]

I just crunched the numbers on 7 global models, UK, GFS, Access, EC, Icon, FR & CMC for the 28 May 12 run for 72 hours. Looked at extremes and the averages. The average is suggesting a major bullseye between Lake Coleridge and Oxford.

I am fearful that not enough of the right people are paying proper attention to this, and they may have failed to prepare their ark's in time. This looks awful for someone. Truly awful

[Cyclone Tracy]

I certainly don't have the local knowledge like others on here, so many of you will have a better idea of the true impacts if models verify. I would think the best hydrologists in the country need to be deployed on this one over the next 96 hours.

[darcyplumb]

I just crunched the numbers on 7 global models, UK, GFS, Access, EC, Icon, FR & CMC for the 28 May 12 run for 72 hours. Looked at extremes and the averages. The average is suggesting a major bullseye between Lake Coleridge and Oxford.

I am fearful that not enough of the right people are paying proper attention to this, and they may have failed to prepare their ark's in time. This looks awful for someone. Truly awful

Totally agree with you on this. I work at one of the local supermarkets in Ashburton and was working last night. Lots of farming people came in and stocked up so are well prepared but a lot of others have no idea. Lots of ‘oh it’s just a bit of rain’ comments. People just don’t understand that 1, it is very dry for this time of year and 2, we just do not see these rainfall amounts on the plains in this timeframe. I’ve lived here for 13 years now and I’ve never seen a forecast like this for us.

[darcyplumb]

Also I should add that we’ve had some very steady rainfall here overnight already. Close to 20mm.

[melja]

Since when has kaikoura and areas south been in marlborough like the metservice warning says.
Area: Canterbury about and north of Amberley, and Marlborough about and south of Kaikoura
We live in Picton not Rangiora as of a month ago, been rain all night here and very heavy this morning.
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[TonyT]

Since when has kaikoura and areas south been in marlborough like the metservice warning says.
Area: Canterbury about and north of Amberley, and Marlborough about and south of Kaikoura
We live in Picton not Rangiora as of a month ago, been rain all night here and very heavy this morning.
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The provincial boundary is the Conway River. Please change your forum setting for location to your new one. Thanks.

[TonyT]

12Z ECMWF ensemble rainfall is closing in nicely now we are less than 3 days out. So the range (for Christchurch, by Monday night) is 50-115mm with the mean at 80mm and the control run at 85mm. Slightly less of the region in the 150mm+ zone now, but most areas other than then far eastern Plains in the 100-150mm range.

The narrow feed of near gale force easterly winds into Pegasus Bay briefly between midnight and 6am Sunday morning (that CT identified earlier - good job!) has to be a concern as it coincides with a high tide (around 6am) and the area is likely to have already received 50mm of rain. Significant easterly swells will be generated. The potential impact on river/lagoon mouth drainage and possible erosion potential in that brief time period need to be highlighted.

[Dean.]

30mm in the gauge already and shes just kicking off.....

[melja]

Since when has kaikoura and areas south been in marlborough like the metservice warning says.
Area: Canterbury about and north of Amberley, and Marlborough about and south of Kaikoura
We live in Picton not Rangiora as of a month ago, been rain all night here and very heavy this morning.
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The provincial boundary is the Conway River. Please change your forum setting for location to your new one. Thanks.

It used to be but isn't currently Tony.

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[TonyT]

The provincial boundary is the Conway River. Please change your forum setting for location to your new one. Thanks.

It used to be but isn't currently Tony.

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Apologies, I wasn't aware of that.

[Cyclone Tracy]

Atmospheric river starting to take shape on the 10am loop with pockets of 25 to 30mm total precip water appearing in the wrap.

http://tropic.ssec.wisc.edu/real-time/m ... anim=html5

[Chris W]

Was up around Gebbies Pass this morning, low cloud making its way across there so plenty moisture around already. Not expecting venturing too far out the rest of the day but hoping the drainage on London St is up to the task!

[JP.]

Just been for a quick run around opawa / St martins. Got home just as a steady shower started. Wind has picked up and the port hills are disappearing behind low cloud.

[Cyclone Tracy]

11:20am water vapour image shows the upper polar injection is about to be severed. The cold core cyclone is soon become rogue unhinged mid latitude cut off low.

[darcyplumb]

Radar lighting up like a Christmas tree now. Let the fun and games begin. Stay safe everyone!

[dogmelon]

11:20am water vapour image shows the upper polar injection is about to be severed. The cold core cyclone is soon become rogue unhinged mid latitude cut off low.

Does that mean its bad, does it?

[Cantab03]

Very litttle rain so far here in the City. 4mm in total and it's now stopped. Hoping the heavy feed zone hits us soon as forecast.

[Awhituobs]

basicly its the rain band that has just passed through Hawkes bay that now needs to re form over the ocean and rotate around and down into eastern South Island, which will happen from 5pm?
I see people on FB saying CHCH has only had some drizzle, which has stopped , and think the forecast is wrong
but the warning period has not even started yet